TY - GEN A1 - Moeck, Jonas Pablo A1 - Oevermann, Michael A1 - Klein, Rupert A1 - Paschereit, Christian Oliver A1 - Schmidt, Heiko T1 - A two-way coupling for modeling thermoacoustic instabilities in a flat flame Rijke tube T2 - Proceedings of the Combustion Institute Y1 - 2009 U6 - https://doi.org/10.1016/j.proci.2008.05.062 SN - 1540-7489 VL - 32 IS - 1 SP - 1199 EP - 1207 ER - TY - GEN A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - HCCI combustion modeling using detailed chemistry coupled to LEM-based advection T2 - Combustion and Flame Y1 - 2008 SN - 1556-2921 VL - 155 IS - 3 SP - 370 EP - 379 ER - TY - CHAP A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Linear eddy modeling of n-heptane combustion in HCCI engines T2 - 12th SIAM International Conference on Numerical Combustion Y1 - 2008 UR - http://www.siam.org/meetings/nc08/prgNC08.pdf ER - TY - CHAP A1 - Movaghar, Amirreza A1 - Linne, Mark A1 - Oevermann, Michael A1 - Meiselbach, Falko T. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Numerical study of liquid breakup at the surface of turbulent liquid jets using One-Dimensional Turbulence T2 - 26th Annual Conference on Liquid Atomization and Spray Systems, ILASS, proceedings of the Conference, Bremen, Germany, 08.09.2014 - 10.09.2014 N2 - This paper presents an investigation of primary breakup of planar turbulent liquid jets and breakup properties at the surface of turbulent jets in still air at standard conditions. Numerical simulations are carried out for jet exit Reynolds number 23000 and Weber numbers in the range [102–107]. Due to the limitation of direct numerical simulation (DNS) to moderate Reynolds numbers, a stochastic 1D ansatz based on the one-dimensional turbulence (ODT) model is used to simulate a planar liquid jet with a high lateral resolution. ODT permits an affordable high resolution of interface and single-phase property gradients which are key for understanding the local behavior. ODT is a stochastic model simulating turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. The most relevant mechanisms that influence the primary breakup of liquid jets are found to be represented accurately based on comparisons to experiments and correlations reported in the literature. Building on this finding, future work will focus on the statistics of droplets generated by primary breakup, both to investigate their relationship to breakup mechanisms and to provide input to models of secondary breakup and subsequent spray evolution. Y1 - 2014 SN - 978-3-00-047070-7 CY - Bremen ER - TY - GEN A1 - Movaghar, Amirreza A1 - Linne, Mark A1 - Oevermann, Michael A1 - Meiselbach, Falko T. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Numerical investigation of turbulent-jet primary breakup using One-Dimensional Turbulence T2 - International Journal of Multiphase Flow N2 - Primary breakup to form droplets at liquid surfaces is an important fundamental process to study as it determines the initial properties of the dispersed phase, which affect mixing rates, secondary breakup, droplet collisions, and flow separation within the dispersed flow region. Primary breakup can be regarded as one of the least developed model components for simulating and predicting liquid jet breakup. How- ever, it is of paramount importance in many technical applications, e.g. fuel injection in engines and spray painting. This paper presents a numerical investigation of primary breakup of a turbulent liquid jet in still air at standard conditions using the one-dimensional turbulence (ODT) modeling framework. ODT is a stochastic model that simulates turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. An important feature of ODT is the resolution of all relevant scales, both temporal and spatial. The restriction to one spatial dimension in ODT permits affordable high resolution of interfacial and single-phase property gradients, which is key to capturing the local behavior of the breakup process and allows simulations at high Reynolds and Weber numbers that are currently not accessible to direct numerical simulations (DNS). This paper summarizes our extensions of the ODT model to simulate geometrically simple jet breakup problems, including representations of Rayleigh wave breakup, turbulent breakup, and shear-driven breakup. Each jet breakup simulation consists of a short temporal channel section to initialize a turbulent velocity profile at the nozzle exit followed by an adjacent jet section. The simulations are carried out for jet exit Reynolds number of 11,500, 23,000, 46,000 and 92,000 while the Weber number is varied within the range 102–107. We present results on breakup statistics including spatial locations of droplet release, droplet sizes and liquid core length. The results on primary breakup are compared to experimental results and models. Y1 - 2017 SN - 1879-3533 VL - 89 SP - 241 EP - 254 ER - TY - GEN A1 - Lignell, David O. A1 - Lansinger, Victoria B. A1 - Medina Méndez, Juan Ali A1 - Klein, Marten A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Fistler, Marco A1 - Oevermann, Michael T1 - One-dimensional turbulence modeling for cylindrical and spherical flows: model formulation and application T2 - Theoretical and Computational Fluid Dynamics N2 - The one-dimensional turbulence (ODT) model resolves a full range of time and length scales and is computationally efficient. ODT has been applied to a wide range of complex multi-scale flows, such as turbulent combustion. Previous ODT comparisons to experimental data have focused mainly on planar flows. Applications to cylindrical flows, such as round jets, have been based on rough analogies, e.g., by exploiting the fortuitous consistency of the similarity scalings of temporally developing planar jets and spatially developing round jets. To obtain a more systematic treatment, a new formulation of the ODT model in cylindrical and spherical coordinates is presented here. The model is written in terms of a geometric factor so that planar, cylindrical, and spherical configurations are represented in the same way. Temporal and spatial versions of the model are presented. A Lagrangian finite-volume implementation is used with a dynamically adaptive mesh. The adaptive mesh facilitates the implementation of cylindrical and spherical versions of the triplet map, which is used to model turbulent advection (eddy events) in the one-dimensional flow coordinate. In cylindrical and spherical coordinates, geometric stretching of the three triplet map images occurs due to the radial dependence of volume, with the stretching being strongest near the centerline. Two triplet map variants, TMA and TMB, are presented. In TMA, the three map images have the same volume, but different radial segment lengths. In TMB, the three map images have the same radial segment lengths, but different segment volumes. Cylindrical results are presented for temporal pipe flow, a spatial nonreacting jet, and a spatial nonreacting jet flame. These results compare very well to direct numerical simulation for the pipe flow, and to experimental data for the jets. The nonreacting jet treatment overpredicts velocity fluctuations near the centerline, due to the geometric stretching of the triplet maps and its effect on the eddy event rate distribution. TMB performs better than TMA. A hybrid planar-TMB (PTMB) approach is also presented, which further improves the results. TMA, TMB, and PTMB are nearly identical in the pipe flow where the key dynamics occur near the wall away from the centerline. The jet flame illustrates effects of variable density and viscosity, including dilatational effects. KW - Cylindrical ODT Y1 - 2018 U6 - https://doi.org/10.1007/s00162-018-0465-1 SN - 0935-4964 SN - 1432-2250 VL - 32 IS - 4 SP - 495 EP - 520 ER - TY - GEN A1 - Somhorst, Joop A1 - Oevermann, Michael A1 - Bovo, Mirko A1 - Denbratt, Ingemar T1 - Evaluation of thermal barrier coatings and surface roughness in a single-cylinder light-duty diesel engine T2 - International Journal of Engine Research N2 - The effect of two thermal barrier coatings and their surface roughness on heat transfer, combustion, and emissions has been investigated in a single-cylinder light-duty diesel engine. The evaluated thermal barrier coating materials were plasma-sprayed yttria-stabilized zirconia and hard anodized aluminum, which were applied on the piston top surface. The main tool for the investigation was cylinder pressure analysis of the high-pressure cycle, from which the apparent rate of heat release, indicated efficiency, and heat losses were derived. For verification of the calculated wall heat transfer, the heat flow to the piston cooling oil was measured as well. Application of thermal barrier coatings can influence engine operating conditions like charge temperature and ignition delay. Therefore, extra attention was paid to choosing stable and repeatable engine operating points. The experimental data were modeled using multiple linear regression to isolate the effects of the coatings and of the surface roughness. The results from this study show that high surface roughness leads to increased wall heat losses and a delayed combustion. However, these effects are less pronounced at lower engine loads and in the presence of soot deposits. Both thermal barrier coatings show a reduction of cycle-averaged wall heat losses, but no improvement in indicated efficiency. The surface roughness and thermal barrier coatings had a significant impact on the hydrocarbon emissions, especially for low-load engine operation, while their effect on the other exhaust emissions was relatively small. KW - Engine KW - efficiency KW - emissions KW - Thermal barrier coating KW - TBC KW - surface roughness KW - MLR KW - regression KW - data model Y1 - 2019 U6 - https://doi.org/10.1177/1468087419875837 SN - 1468-0874 SN - 2041-3149 VL - 22(2021) SP - 890 EP - 910 ER - TY - GEN A1 - Pollack, Martin A1 - Pütz, Michele A1 - Marchisio, Daniele L A1 - Oevermann, Michael A1 - Hasse, Christian T1 - Zero-flux approximations for multivariate quadrature-based moment methods T2 - Journal of Computational Physics N2 - The evolution of polydisperse systems is governed by population balance equations. A group of efficient solution approaches are the moment methods, which do not solve for the number density function (NDF) directly but rather for a set of its moments. While this is computationally efficient, a specific challenge arises when describing the fluxes across a boundary in phase space for the disappearance of elements, the so-called zero-flux. The main difficulty is the missing NDF-information at the boundary, which most moment methods cannot provide. Relevant physical examples are evaporating droplets, soot oxidation or particle dissolution. In general, this issue can be solved by reconstructing the NDF close to the boundary. However, this was previously only achieved with univariate approaches, i.e. considering only a single internal variable. Many physical problems are insufficiently described by univariate population balance equations, e.g. droplets in sprays often require the temperature or the velocity to be internal coordinates in addition to the size. In this paper, we propose an algorithm, which provides an efficient multivariate approach to calculate the zero-fluxes. The algorithm employs the Extended Quadrature Method of Moments (EQMOM) with Beta and Gamma kernel density functions for the marginal NDF reconstruction and a polynomial or spline for the other conditional dimensions. This combination allows to reconstruct the entire multivariate NDF and based on this, expressions for the disappearance flux are derived. An algorithm is proposed for the whole moment inversion and reconstruction process. It is validated against a suite of test cases with increasing complexity. The influence of the number of kernel density functions and the configuration of the polynomials and splines on the accuracy is discussed. Finally, the associated computational costs are evaluated. KW - Number density function KW - Population balance equation KW - Method of moments KW - EQMOM KW - Multivariate KW - Evaporation Y1 - 2019 U6 - https://doi.org/10.1016/j.jcp.2019.108879 SN - 0021-9991 IS - 398 ER - TY - GEN A1 - Arshad, Salman A1 - Kong, Bo A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A strategy for large-scale scalar advection in large eddy simulations that use the linear eddy sub-grid mixing model T2 - International Journal of Numerical Methods for Heat and Fluid Flow N2 - Purpose: The purpose of this numerical work is to present and test a new approach for large-scale scalar advection (splicing) in large eddy simulations (LES) that use the linear eddy sub-grid mixing model (LEM) called the LES-LEM. Design/methodology/approach: The new splicing strategy is based on an ordered flux of spliced LEM segments. The principle is that low-flux segments have less momentum than high-flux segments and, therefore, are displaced less than high-flux segments. This strategy affects the order of both inflowing and outflowing LEM segments of an LES cell. The new splicing approach is implemented in a pressure-based fluid solver and tested by simulation of passive scalar transport in a co-flowing turbulent rectangular jet, instead of combustion simulation, to perform an isolated investigation of splicing. Comparison of the new splicing with a previous splicing approach is also done. Findings: The simulation results show that the velocity statistics and passive scalar mixing are correctly predicted using the new splicing approach for the LES-LEM. It is argued that modeling of large-scale advection in the LES-LEM via splicing is reasonable, and the new splicing approach potentially captures the physics better than the old approach. The standard LES sub-grid mixing models do not represent turbulent mixing in a proper way because they do not adequately represent molecular diffusion processes and counter gradient effects. Scalar mixing in turbulent flow consists of two different processes, i.e. turbulent mixing that increases the interface between unmixed species and molecular diffusion. It is crucial to model these two processes individually at their respective time scales. The LEM explicitly includes both of these processes and has been used successfully as a sub-grid scalar mixing model (McMurtry et al., 1992; Sone and Menon, 2003). Here, the turbulent mixing capabilities of the LES-LEM with a modified splicing treatment are examined. Originality/value: The splicing strategy proposed for the LES-LEM is original and has not been investigated before. Also, it is the first LES-LEM implementation using unstructured grids. KW - Large eddy simulations KW - LES-LEM KW - Linear eddy model KW - Passive scalar mixing KW - Splicing KW - Turbulent jet flow Y1 - 2018 U6 - https://doi.org/10.1108/HFF-09-2017-0387 SN - 0961-5539 VL - 28 IS - 10 SP - 2463 EP - 2479 ER - TY - GEN A1 - Lackmann, Tim A1 - Nygren, Andreas A1 - Karlsson, Anders A1 - Oevermann, Michael T1 - Investigation of turbulence–chemistry interactions in a heavy-duty diesel engine with a representative interactive linear eddy model T2 - International Journal of Engine Research N2 - Simulations of a heavy-duty diesel engine operated at high-load and low-load conditions were compared to each other, and experimental data in order to evaluate the influence of turbulence–chemistry interactions on heat release, pressure development, flame structure, and temperature development are quantified. A recently developed new combustion model for turbulent diffusion flames called representative interactive linear eddy model which features turbulence–chemistry interaction was compared to a well-stirred reactor model which neglects the influence of turbulent fluctuations on the mean reaction rate. All other aspects regarding the spray combustion simulation like spray break-up, chemical mechanism, and boundary conditions within the combustion chamber were kept the same in both simulations. In this article, representative interactive linear eddy model is extended with a progress variable, which enables the model to account for a flame lift-off and split injection, when it is used for diffusion combustion. In addition, the extended version of representative interactive linear eddy model offers the potential to treat partially premixed and premixed combustion as well. The well-stirred reactor model was tuned to match the experimental results, thus computed pressure and apparent heat release are in close agreement with the experimental data. Representative interactive linear eddy model was not tuned specifically for the case and thus the computed results for pressure and heat release are in reasonable agreement with experimental data. The computational results show that the interaction of the turbulent flow field and the chemistry reduce the peak temperatures and broaden up the turbulent flame structure. Since this is the first study of a real combustion engine (metal engine) with the newly developed model, representative interactive linear eddy model appears as a promising candidate for predictions of spray combustion in engines, especially in combustion regimes where turbulence–chemistry interaction plays an even more important role like, example given, in low-temperature combustion or combustion with local extinction and re-ignition. KW - Representative interactive linear eddy model KW - turbulent spray flame KW - turbulence–chemistry interaction KW - diesel engine Y1 - 2018 U6 - https://doi.org/10.1177/1468087418812319 SN - 1468-0874 VL - 21 IS - 8 SP - 1469 EP - 1479 ER - TY - GEN A1 - Lackmann, Tim A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A representative linear eddy model for simulating spray combustion in engines (RILEM) T2 - Combustion and Flame N2 - The design of new combustion concepts for low emission, high efficiency internal combustion engines often leads to combustion under low temperature conditions. Under those conditions, the assumption of fast chemistry, which has been the cornerstone of many turbulent combustion models, is not strictly valid anymore and the validity and applicability of classical combustion models such as flamelet models might be limited. In this paper we present an updated version of a recently developed regime independent modeling approach for turbulent non-premixed combustion with an emphasis on applications to internal combustion engines. The model utilizes the mode- and regime-independent linear eddy model (LEM) as a combustion and micro-mixing model in a representative way. This is achieved by time advancing only one LEM realization representing the combustion process in the whole engine domain and coupling it to a RANS simulation with a presumed β-function PDF approach for the mixture fraction. The use of LEM rather than flamelet combustion closure has several benefits, an important one being regime independence. Additionally, LEM incorporates a physically based representation of the stochastic variability of turbulent eddy motions, implying an intrinsic representation of scalar dissipation rate fluctuations. In order to capture key features of engine spray-combustion environments, the LEM methodology is extended by introducing a conical LEM domain to approximate spray spatial development, fuel vapor input based on CFD-prescribed spray evaporation, and a representation of large scale turbulent motions distinct from the inertial-range turbulence that develops at smaller scales. The representative character of LEM states is evaluated by comparing mixture fraction statistics and scalar dissipation rates generated by LEM and the CFD. The performance and predictive capability of the model for typical engine applications is evaluated by simulating a standard test case – Spray B of the Engine Combustion Network (ECN) – and comparing the results with experimental data. The results demonstrate the capability of the model to represent the spray combustion process with reasonable accuracy but also reveal some limitations. The limitations and shortcomings of the model are discussed and an outlook for further development of the approach into a regime- and mode-independent combustion model for internal engine applications is given. KW - Turbulent combustion KW - Regime independent KW - Engine simulation KW - Linear eddy model Y1 - 2018 U6 - https://doi.org/10.1016/j.combustflame.2018.02.008 SN - 0010-2180 VL - 193 SP - 1 EP - 15 ER - TY - GEN A1 - Chen, Boxiong A1 - Oevermann, Michael T1 - An Eulerian stochastic field cavitation model coupled to a pressure based solver T2 - Computer and Fluids N2 - Probability density functions (PDF) and the relevant methods have been widely used to describe non-linear phenomena in the realm of turbulence modelling and CFD. In order to solve PDF transport equations, the main trend of previous studies rely on Monte Carlo method with Lagrangian particle tracking. However, as with any Lagrangian based approach, the scalability of the parallelized simulations of such method is less than satisfactory. An Eulerian stochastic field model has been presented recently by Dumond et al. [1] to simulate cavitating flows. Their model uses a fully compressible density based solver. Here we present an adapted version using an iso-thermal cavitation model adopting the homogeneous mixture assumption in a pressure based flow solver which is more relevant to engine simulations. A PDF method is used to represent a distribution of vapour volume fractions, based on which the Eulerian stochastic field (ESF) method is applied to perform a three-dimensional large eddy simulation (LES) of the cavitation phenomena inside an academic fuel injector configuration. The numerical model is based on a volume of fluids approach and coupled with a pressure based solver for the flow field, and is implemented in the framework of the open source C++ toolbox OpenFOAM. The result of the ESF simulation is compared against that from a typical single volume fraction solver for validation. Vortex structures and its correspondence to cavitation are shown, and the behaviour of the PDF at different probe locations at different times are acquired to demonstrate the potential of the ESF model in capturing both transient and stochastically steady cavitation. KW - Multiphase flow KW - Cavitation KW - Volume of fluid KW - Eulerian stochastic field method Y1 - 2018 U6 - https://doi.org/10.1016/j.compfluid.2017.12.002 SN - 0045-7930 VL - 162 SP - 1 EP - 10 ER - TY - GEN A1 - Movaghar, Amirreza A1 - Linne, Mark A1 - Herrmann, Marcus A. A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - Modeling and numerical study of primary breakup under diesel conditions T2 - International Journal of Multiphase Flow N2 - A recently introduced stochastic model for reduced numerical simulation of primary jet breakup is evaluated by comparing model predictions to DNS results for primary jet breakup under diesel conditions. The model uses one-dimensional turbulence (ODT) to simulate liquid and gas time advancement along a lateral line of sight. This one-dimensional domain is interpreted as a Lagrangian object that is advected downstream at the jet bulk velocity, thus producing a flow state expressed as a function of streamwise and lateral location. Multiple realizations are run to gather ensemble statistics that are compared to DNS results. The model incorporates several empirical extensions of the original ODT model that represent the phenomenology governing the Weber number dependence of global jet structure. The model as previously formulated, including the assigned values of tunable parameters, is used here without modification in order to test its capability to predict various statistics of droplets generated by primary breakup. This test is enabled by the availability of DNS results that are suitable for model validation. Properties that are examined are the rate of bulk liquid mass conversion into droplets, the droplet size distribution, and the dependence of droplet velocities on droplet diameter. Quantities of greatest importance for engine modeling are found to be predicted with useful accuracy, thereby demonstrating a more detailed predictive capability by a highly reduced numerical model of primary jet breakup than has previously been achieved. KW - Spray KW - Primary breakup KW - Turbulence KW - One-dimensional turbulence KW - Direct numerical simulation (DNS) Y1 - 2018 U6 - https://doi.org/10.1016/j.ijmultiphaseflow.2017.09.002 SN - 0301-9322 VL - 98 SP - 110 EP - 119 ER - TY - GEN A1 - Gerber, Stephan A1 - Oevermann, Michael T1 - A two dimensional Euler-Lagrangian model of wood gasification in a charcoal bed — Particle histories T2 - Powder Technology N2 - An Euler-Lagrangian simulation applied to wood gasification in a fluidized bed is used to investigate individual particle histories and to provide a statistical analysis for temperature, apparent density as well as radial and axial positions of charcoal and dry wood particles. The model and several parameter variations have been discussed in detail in previous articles [1], [2], [3]. Based on simulation results we find much higher particle heating rates than typically used to measure kinetic data for, e.g., pyrolysis models. Although we presented a rather complex interplay of particle heating rate, biomass decomposition, particle shrinkage and particle fluidization the simulation results emphasize the importance of the usage of realistic particle size distributions for the initial bed as well as the fuel inlet. Furthermore, particle shrinkage data in combination with mass decomposition data appear to be crucial for realistic simulations. KW - Wood gasification KW - Pyrolysis KW - Discrete element KW - Fluidized bed KW - Charcoal bed KW - Euler-Lagrange Y1 - 2018 U6 - https://doi.org/10.1016/j.powtec.2017.10.032 SN - 0032-5910 VL - 324 SP - 5 EP - 15 ER - TY - GEN A1 - Gerber, Stephan A1 - Oevermann, Michael T1 - A two dimensional Euler-Lagrangian model of wood gasification in a charcoal bed - Part III: parameter influence and comparison T2 - Powder Technology N2 - The efficient utilization of biomass in fluidized bed reactors depends on numerous operation conditions and parameters which can be investigated systematically with computational models. Based on a previous study [1] we compare a base scenario which mimics the experimental situation with different parameter settings for an Euler-Lagrangian simulation of wood gasification in a fluidized charcoal bed. For the varied parameters superficial velocity, reactor wall temperature, air inlet temperature, wood particle size, and the wood inlet temperature we analyse the simulation results based on data for temporal evolution of reactor outlet temperature, averaged particle temperature, overall wood mass, overall charcoal mass, concentrations of several gaseous species (N2, CO, CO2, H2, H2O, CH4, C2H2, and three virtual tar components) and axial barycenter data of particles bed mass. Furthermore we show time averaged data for gaseous species and gas phase temperature at the reactor outlet. At the end we critically examine our findings under consideration of the models opportunities and limitations. KW - Wood gasification KW - Fluidized bed KW - Euler-Lagrange KW - Discrete element method KW - Charcoal bed KW - Gasification Y1 - 2017 U6 - https://doi.org/10.1016/j.powtec.2016.12.057 SN - 0032-5910 VL - 310 SP - 163 EP - 174 ER - TY - GEN A1 - Wadekar, Sandip A1 - Janas, Peter A1 - Oevermann, Michael T1 - Large-eddy simulation study of combustion cyclic variation in a lean-burn spark ignition engine T2 - Applied Energy N2 - Multi-cycle large-eddy simulation (LES) was performed to investigate combustion cyclic variability (CCV) in a single cylinder spark ignition engine with a homogeneous lean ( = 1.25) isooctane-air mixture. The aim was to obtain physical insights into the early stage of combustion and its influence on CCV. Propagation of the flame was modeled by a transport equation for the filtered flame surface density within the LES framework. The ignition process was represented by the imposed stretch spark ignition model (ISSIM-LES). Ten consecutive cold flow LES cycles followed by two initialization cycles (12 cycles in total) were used to perform the reactive simulations concurrently. The simulation results were compared with experimental data. Although the number of computed cycles was fairly low, the LES was able to reproduce the cyclic variability observed in experiments both quantitatively and qualitatively. Firstly, validation of the simulation was done by comparing measured pressure traces. Secondly, correlations between the timing of the 10% fuel burnt mass fraction with early flame kernel growth and initial-to-turbulent transition period (in which there was an asymmetric flame kernel that persisted through the early development periods) were determined. Thirdly, calculated results of the flame propagation were analyzed at two cross-sections (in swirl and tumble planes) of the combustion chamber, which highlighted differences in instantaneous flame structures and propagation characteristics between the fastest and slowest cycles. Good overall agreement was obtained between the measurements and simulation data. The results revealed that the instantaneous velocity and fluctuation of flows around the spark vicinity affect growth of the early flame kernel and cause combustion cyclic variability. KW - Large-eddy simulation KW - Combustion cyclic variation KW - Flame surface density KW - Ignition modelling KW - Lean combustion Y1 - 2019 U6 - https://doi.org/10.1016/j.apenergy.2019.113812 SN - 0306-2619 VL - 255 ER - TY - GEN A1 - Gerber, Stephan A1 - Oevermann, Michael T1 - A two dimensional Euler-Lagrangian model of wood gasification in a charcoal bed - Part II: parameter influence and comparison T2 - Particuology N2 - A Euler–Lagrangian simulation was employed for a comprehensive parameter study of wood gasification in a fluidized charcoal bed. The parameters that were varied include the initial bed temperature, fuel mass flow rate, inert tar fraction, and kinetic energy losses caused by particle–particle and particle–wall collisions. The results of each parameter variation are compared with a base scenario, previously described in detail in Part I of this study (Gerber & Oevermann, 2014). The results are interpreted by comparing the reactor outlet temperature, averaged particle temperature, overall wood mass, overall charcoal mass, concentrations of several gaseous species, and axial barycenter data for particles obtained with different sets of parameters. The inert tar fraction and fuel mass flow rate are the most sensitive parameter, while the particle–particle and particle–wall contact parameters have only a small impact on the results. Increasing the reactive tar components by 19% almost doubled the amount of reactive tars at the reactor outlet, while decreasing the restitution coefficients of the particle collisions by 0.2 results in higher overall gas production but almost no change in bed height. Herein, our numerical results are discussed in detail while assessing the model restrictions. KW - Wood gasification simulation KW - Gas–solid flow KW - Discrete element method KW - Pyrolysis KW - Gasification KW - Charcoal Y1 - 2017 U6 - https://doi.org/10.1016/j.partic.2017.01.004 SN - 1674-2001 VL - 35 SP - 22 EP - 30 ER - TY - GEN A1 - Lackmann, Tim A1 - Hewson, John A1 - Knaus, Robert A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - Stochastic modeling of unsteady extinction in turbulent non-premixed combustion T2 - Proceedings of the Combustion Institute N2 - Turbulent fluctuations of the scalar dissipation rate have a major impact on extinction in non-premixed combustion. Recently, an unsteady extinction criterion has been developed (Hewson, 2013) that predicts extinction dependent on the duration and the magnitude of dissipation rate fluctuations exceeding a critical quenching value; this quantity is referred to as the dissipation impulse. The magnitude of the dissipation impulse corresponding to unsteady extinction is related to the difficulty with which a flamelet is exintguished, based on the steady-state S-curve. In this paper we evaluate this new extinction criterion for more realistic dissipation rates by evolving a stochastic Ornstein–Uhlenbeck process for the dissipation rate. A comparison between unsteady flamelet evolution using this dissipation rate and the extinction criterion exhibit good agreement. The rate of predicted extinction is examined over a range of Damköhler and Reynolds numbers and over a range of the extinction difficulty. The results suggest that the rate of extinction is proportional to the average dissipation rate and the area under the dissipation rate probability density function exceeding the steady-state quenching value. It is also inversely related to the actual probability that this steady-state quenching dissipation rate is observed and the difficulty of extinction associated with the distance between the upper and middle branches of the S-curve. KW - Extinction KW - Unsteady flames KW - Non-premixed flame KW - Scalar dissipation rate KW - Turbulence Y1 - 2016 U6 - https://doi.org/10.1016/j.proci.2016.07.014 SN - 0082-0784 VL - 36 IS - 2 SP - 1677 EP - 1684 ER - TY - GEN A1 - Somhorst, Joop A1 - Uczak De Goes, Wellington A1 - Oevermann, Michael A1 - Bovo, Mirko T1 - Experimental Evaluation of Novel Thermal Barrier Coatings in a Single Cylinder Light Duty Diesel Engine T2 - SAE Technical Papers N2 - The objective of this investigation was to improve the thermal properties of plasma sprayed thermal barrier coatings (TBC) for internal combustion engines. There is a need for further reduction of thermal conductivity and volumetric heat capacity and the negative effects on heat loss and combustion phasing of surface roughness and permeable porosity, typical for plasma sprayed coatings, should be minimized. Four measures for improvement of TBC properties were evaluated: i) modification of the coating's microstructure by using a novel suspension plasma spraying method, ii) application of gadolinium-zirconate, a novel ceramic material with low thermal conductivity, iii) polishing of the coating to achieve low surface roughness, and iv) sealing of the porous coating surface with a polysilazane. Six coating variants with different combinations of the selected measures were applied on the piston crown and evaluated in a single cylinder light duty diesel engine. The experimental data was modeled with multiple linear regression to obtain confidence intervals for the measurement results and to correct the data for variations of surface roughness, combustion phasing and compression ratio for the different pistons. The main tool for evaluation of the coating properties was cylinder pressure analysis, providing the apparent rate of heat release, indicated efficiency, wall heat loss, and exhaust loss. The new TBC microstructure from suspension plasma spraying in combination with the use of gadolinium-zirconate showed promising results with respect to indicated efficiency and heat loss reduction. Y1 - 2019 U6 - https://doi.org/10.4271/2019-24-0062 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Wadekar, Sandip A1 - Oevermann, Michael A1 - Lipatnikov, Andrei T1 - Large Eddy Simulation of Stratified Combustion in Spray-guided Direct Injection Spark-ignition Engine T2 - SAE Technical Papers N2 - Stratified combustion in gasoline engines constitutes a promising means of achieving higher thermal efficiency for low to medium engine loads than that achieved with combustion under standard homogeneous conditions. However, creating a charge that leads to a stable efficient low-emission stratified combustion process remains challenging. Combustion through a stratified charge depends strongly on the dynamics of the turbulent fuel-air mixing process and the flame propagation. Predictive simulation tools are required to elucidate this complex mixing and combustion process under stratified conditions. For the simulation of mixing processes, combustion models based on large-eddy turbulence modeling have typically outperformed the standard Reynolds averaged Navier-Stokes methods. Therefore, we investigated spray-guided stratified combustion in a single cylinder engine using large-eddy turbulence modeling with a variant of the flame speed closure (FSC) model for premixed turbulent combustion. This model reveals the influence of the mixture composition on the flame speed. The effect of fluctuations in the composition were accounted for by using a presumed probability density function (PDF) approach for the mixture fraction. The fuel injection process was modeled with a standard Lagrangian spray model. More importantly, the measured in-cylinder pressure traces for three different loading cases with varying injection and ignition timings (leading to different levels of stratification) were accurately reproduced by the simulation. High-speed video images were used to evaluate the ability of the model to accurately simulate flame propagation under stratified conditions. The influence of mixture fluctuations on flame propagation was also investigated. KW - Single cylinder engines KW - Ignition timing KW - Combustion and combustion processes KW - Fuel injection Y1 - 2018 U6 - https://doi.org/10.4271/2018-01-1420 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Fistler, Marco A1 - Kerstein, Alan R. A1 - Wunsch, Scott A1 - Oevermann, Michael T1 - Turbulence modulation in particle-laden stationary homogeneous shear turbulence using one-dimensional turbulence T2 - Physical Review Fluids N2 - Turbulence modulation in particle-laden stationary homogeneous shear turbulence (HST) is investigated using one-dimensional turbulence (ODT), a low-dimensional stochastic flow simulation model. For this purpose, an ODT formulation previously used to study turbulence modulation in forced homogeneous isotropic turbulence (HIT) is extended, so that the model emulates the anisotropic character of HST and, potentially, anisotropic turbulence in general. This is done by limiting the kinetic-energy redistribution during an eddy event to an exchange involving two velocity components, where the three possible choices of the omitted component define three eddy types whose relative likelihoods control the anisotropy. Comparisons of ODT and direct-numerical-simulation results with reference to signatures of turbulence modulation are the basis of a broader ODT parameter study that is reported. Owing to the reduced dimensionality of ODT, it is found that the fidelity of the model for single-phase HST does not extend to particle effects on flow anisotropy, but for quantities averaged over components, parametric trends are captured. The consistent approach to case comparisons that was introduced in the HIT study to evaluate sensitivities to particle-phase parameters in a given flow configuration is extended here to a cross-comparison of HST and HIT model results, and its efficacy is again confirmed. The results provide an overall characterization of the potential for ODT to support the incorporation of particle-induced turbulence modulation into subgrid-scale closures of large-eddy simulations. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevFluids.5.124303 SN - 2469-990X VL - 5 IS - 12 ER - TY - GEN A1 - Wadekar, Sandip A1 - Yamaguchi, Akichika A1 - Oevermann, Michael T1 - Large-Eddy Simulation on the Effects of Fuel Injection Pressure on the Gasoline Spray Characteristics T2 - SAE Technical Papers N2 - Increasing the injection pressure in gasoline direct injection engines has a substantial potential to reduce emissions while maintaining a high efficiency in spark ignition engines. Present gasoline injectors are operating in the range of 20 MPa to 25 MPa. Now there is an interest in higher fuel injection pressures, for instance, around 40 MPa, 60 MPa and even higher pressures, because of its potential for further emission reduction and fuel efficiency improvements. In order to fully utilize the high-pressure fuel injection technology, a fundamental understanding of gasoline spray characteristics is vital to gain insight into spray behavior under such high injection pressures. The understanding achieved may also be beneficial to improve further model development and facilitate the integration of such advanced injection systems into future gasoline engines. In the present study, a gasoline fuel spray has been investigated over a range of fuel injection pressures from 40 to 150 MPa through a numerical simulation study. The numerical calculations have been performed in a constant volume chamber under non-vaporizing conditions to best match the experimental setup. The numerical model utilized a large-eddy simulation (LES) approach for the gas flow and a standard Lagrangian spray model for the liquid phase. The spray atomization has been modeled using the Kelvin Helmholtz - Rayleigh Taylor (KH-RT) atomization model with a droplet size distribution from the injector assumed to follow a Rosin-Rammler distribution function. Simulation results for the spray liquid penetration length are validated with experimental findings under different fuel injection pressures. Afterwards, an arithmetic mean droplet diameter (D10) and a Sauter mean droplet diameter (D32) as a function of pressure are compared against the measured droplet diameters. Simulated drop size distributions are presented and compared with measured droplet sizes. The results indicate that a high fuel injection pressure increases the liquid penetration length and significantly reduces droplet sizes. The results also exhibit that the SMD decreases from 13.4 μm to 7.5 μm, when injection pressure changes from 40 MPa to 150 MPa and that probability of finding the 5-9 μm droplet diameter decreases from 72% to 40% for the injection pressure drops from 150 MPa to 40 MPa. KW - Spark ignition engines KW - Fuel injection KW - Fuel economy KW - Energy conservation Y1 - 2019 U6 - https://doi.org/10.4271/2019-01-0060 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Somhorst, Joop A1 - Oevermann, Michael A1 - Bovo, Mirko A1 - Denbratt, Ingemar T1 - A Method to Evaluate the Compression Ratio in IC Engines with Porous Thermal Barrier Coatings T2 - SAE Technical Papers N2 - The compression ratio is an important engine design parameter. It determines to a large extend engine properties like the achievable efficiency, the heat losses from the combustion chamber and the exhaust losses. The same properties are affected by insulation of the combustion chamber. It is therefore especially important to know the compression ratio when doing experiments with thermal barrier coatings (TBC). In case of porous TBCs, the standard methods to measure the compression ratio can give wrong results. When measuring the compression ratio by volume, using a liquid, it is uncertain if the liquid fills the total porous volume of the coating. And for a thermodynamic compression ratio estimation, a model for the heat losses is needed, which is not available when doing experiments with insulation. The subject of this paper is the evaluation of an alternative method to assess the compression ratio. It is based on motored cylinder pressure data like other thermodynamic methods but does not need a model for the heat losses. The validation and application of the method is done with data from experiments involving two types of porous TBCs, performed on a light duty single cylinder diesel engine. The results indicate that the proposed method accurately predicts the compression ratio for porous thermal barrier coatings. KW - Combustion chambers KW - Combustion and combustion processes KW - Coatings, colorants, and finishes KW - Insulation Y1 - 2018 U6 - https://doi.org/10.4271/2018-01-1778 SN - 2688-3627 SN - 0148-7191 ER - TY - GEN A1 - Wadekar, Sandip A1 - Oevermann, Michael T1 - Large-Eddy Simulation Study of Ultra-High Fuel Injection Pressure on Gasoline Sprays T2 - Flow, Turbulence and Combustion N2 - The development of gasoline spray at ultra-high injection pressures was analyzed using Large-Eddy simulation (LES). Two different nozzle hole geometries, divergent and convergent shape, were considered to inject the fuel at injection pressures ranging from 200 to 1500 bar inside a constant volume spray chamber maintained at atmospheric conditions. The discrete droplet phase was treated using a Lagrangian formulation together with the standard spray sub-models. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on the spray development. The calibrated model was then used to investigate the impact of ultra-high injection pressures on mean droplet size and droplet size distribution. In addition, the spray-induced large-scale eddies and entrainment rate were evaluated at different ultra-high injection pressures. Overall, simulation results showed a good agreement with available measurement data. At ultra-high injection pressures mean droplet sizes were significantly reduced and comprised very high velocities. Integral length scales of spray-induced turbulence and air entrainment rate into the spray were larger at higher injection pressure compared to lower ones. KW - Sprayinduced turbulence KW - Ultra-high injection pressure KW - Large-Eddy simulation KW - Air-entrainment KW - Gasoline spray Y1 - 2020 U6 - https://doi.org/10.1007/s10494-020-00231-0 SN - 1573-1987 SN - 1386-6184 VL - 107 (2021) IS - 1 SP - 149 EP - 174 ER - TY - GEN A1 - Pütz, Michele A1 - Movaghar, Amirreza A1 - Oevermann, Michael T1 - Numerical simulation of a gasoline spray using one-dimensional turbulence for primary atomization T2 - ICLASS 2018 - 14th International Conference on Liquid Atomization and Spray Systems N2 - Predictive and reliable simulations have the potential to constitute a valuable tool for the optimization of spray systems if accurate submodels are developed for the entire range of the governing processes. The primary breakup of the turbulent liquid jet is one the most important mechanisms in sprays, yet the least developed in terms of numerical modeling. The most accurate method to simulate primary breakup is the proper resolution of liquid-gas interfaces and turbulent flow structures. However, a wide range of relevant length and time scales implicate grid requirements that are often prohibitive for real engineering applications. The most widely used method in practice is still the representation of both the continuous liquid core and the dispersed phase by means of discrete Lagrangian particles evolving in and interacting with the Eulerian gas phase. The available models for primary breakup are mainly phenomenological and involve a number of empirical constants. The one-dimensional turbulence (ODT) model is an alternative stochastic approach to model turbulence in flows with a dominant direction of property gradients. The stochastic representation of turbulent eddies on a one-dimensional domain enables high resolution at moderate computational costs. Applications of ODT to atomization revealed a great potential in recent studies. The objective of the present study is to combine ODT as a primary breakup model with a conventional Eulerian-Lagrangian method for the further spray evolution in order to asses ODT as a submodel in full spray models. Our numerical investigations were conducted on the ECN spray G, a gasoline-like, evaporating spray. The results in terms of spray penetration are encouraging, though the applicability of ODT to the transient injection phase and effects on additional spray characteristics require further investigation. KW - Breakup KW - Numericsl simulation KW - ECN Spray G KW - ODT KW - One-dimensional turbulence modeling KW - Gasoline Y1 - 2018 UR - https://research.chalmers.se/publication/519110 ER - TY - GEN A1 - Fistler, Marco A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A new LES subgrid-scale approach for turbulence modulation by droplets T2 - ICLASS 14th Triennial International Conference on Liquid Atomization and Spray Systems Chicago, USA, 2018-07-21 - 2018-07-26 N2 - We present a new modelling approach for turbulence modulation by droplets on the subgrid-scale (SGS) level of Large-Eddy-Simulations (LES). Many SGS models exist for the effect of gas phase SGS on the droplet phase, but very few for the mechanisms vice versa on the turbulent intensity of the gas phase. The reasons are a lack of physical understanding and limited computational resources for extensive DNS studies. To address both problems a dimension-reduced and consequently less costly model, namely One-Dimensional- Turbulence (ODT), is used to gather information about this specific flow phenomena. ODT is a stochastic tool simulating turbulent flows along a notional 1D line of sights. For modeling the turbulent advection instantaneous maps are applied to the line which represent the effect of individual eddies on property fields and the dispersed phase. After validating the general test case of a droplet-laden shear flow against DNS data, a concept is presented on how to gather turbulence modulation for several parameter ranges in a data base and how to make them accessible on the flight for LES. The three most significant parameters, the unladen flow Reynolds number, the droplet loading and the particle momentum number, are chosen to construct an efficient data base. KW - Turbulence modulation KW - ODT KW - One-Dimensional-Turbulence KW - Particle-laden Y1 - 2018 UR - https://research.chalmers.se/en/publication/519108 ER - TY - CHAP A1 - Movaghar, Amirreza A1 - Chiodi, Robert A1 - Desjardins, Olivier A1 - Oevermann, Michael A1 - Kerstein, Alan R. T1 - A Subgrid-Scale Model for Large-Eddy Simulation of Liquid/Gas Interfaces Based on One-Dimensional Turbulence T2 - Turbulent Cascades II N2 - The interface/turbulence interaction between two fluids in a turbulent environment has an important role in many technical processes, e.g. primary liquid atomization in combustion devices. Primary atomization has a significant role in spray formation and its characteristics. The resulting dynamics typically span 4–6 orders of magnitude in length scales, making detailed numerical simulations exceedingly expensive. This motivates the need for modeling approaches based on spatial filtering such as large-eddy simulation (LES). In this paper, a new approach based on One-Dimensional turbulence (ODT) is presented to describe the subgrid interface dynamics. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps that represent the effects of individual turbulent eddies on property fields. It provides affordable high resolution of interface creation and property gradients within each phase, which are key for capturing the local behavior as well as overall trends. ODT has previously been shown to reproduce the main features of an experimentally determined regime diagram for primary jet breakup. Here a new approach called VODT is presented which produces a size-conditioned as well as a total time rate of generation of droplets for given flow conditions at an interface. At the LES level, the total droplet generation from VODT is interpreted as a rate of mass conversion of LES-resolved liquid into unresolved droplets. Preliminary results of applying VODT to a cell with a planar-shear-layer are discussed at the end of the paper. KW - combustion KW - Large eddy simulation KW - scalar dissipation Y1 - 2019 SN - 978-3-030-12547-9 SN - 978-3-030-12546-2 U6 - https://doi.org/10.1007/978-3-030-12547-9_10 SP - 83 EP - 91 PB - Springer Nature Switzerland AG CY - Schweiz ER - TY - GEN A1 - Somhorst, Joop A1 - Oevermann, Michael T1 - Effects of thermal barrier coating porosity on combustion and heat losses in a light duty diesel engine T2 - International Journal of Engine Research N2 - Plasma sprayed thermal barrier coatings (TBCs), applied in internal combustion engines, can have a profound impact on the apparent rate of heat release. Upon fuel jet contact with the piston wall, the heat loss seems to increase compared to an uncoated piston and combustion appears delayed. Permeable porosity of plasma sprayed TBCs is identified as one of the possible causes for this unwanted effect. In this article the impact of open porosity and sealing of the TBC surface are investigated with single cylinder engine experiments and with simulations. Based on the results, a mechanism is presented to explain the observations. KW - Thermal barrier coating KW - Porosity KW - Insulation KW - Combustion engine KW - Crevice effect KW - Heat transfer KW - Fuel entrainment Y1 - 2024 U6 - https://doi.org/10.1177/14680874231215526 SN - 1468-0874 VL - 25 (2024) IS - 5 SP - 940 EP - 958 ER - TY - GEN A1 - Medina Méndez, Juan Ali A1 - Fistler, Marco A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Riebel, Ulrich T1 - Economical map-based turbulence models: Developments and perspectives for the numerical analysis of electrostatic precipitation T2 - Book of Abstracts PARTEC International Congress on Particle Technology, September 26-28, 2023, Nürnberg Y1 - 2023 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Medina_2023_Extended Abstract_Template_PARTEC_ODT.pdf SP - 634 EP - 638 PB - VDI Verlag GmbH CY - Düsseldorf ER - TY - GEN A1 - Menon, Abhilash A1 - Kerstein, Alan A1 - Oevermann, Michael T1 - Assessing the multi-regime capability of the Super-Grid Linear Eddy Model (SG-LEM) using the Darmstadt multi-regime burner T2 - Flow, Turbulence and Combustion N2 - AbstractRecent advances in combustion modelling for Large Eddy Simulation (LES) have increasingly utilised lower-dimensional manifolds, such as Flamelet Generated Manifolds and Flamelet/Progress Variable methods, due to their computational efficiency. These methods typically rely on one-dimensional representations of flame structures, often assuming premixed or non-premixed configurations. However, practical combustion devices frequently operate under partially-premixed conditions and present challenges due to mixture inhomogeneities and complex flow features. The Linear Eddy Model (LEM) offers an alternative by directly simulating turbulence-chemistry interactions without presuming specific flame structures. However, traditional LES-LEM approaches are computationally quite expensive due to the need for resolved LEM domains to be embedded in every LES cell.The authors developed the Super-Grid LEM (SG-LEM) method (Comb. Theor. Model.  28, 2024) to address these computational challenges by coarse-graining the LES mesh and embedding individual LEM domains within clusters of LES cells. This study evaluates SG-LEM in the context of the Multi-Regime Burner (MRB) introduced by Butz et al. (Combust. Flame, 210, 2019), which features both premixed and non-premixed flame characteristics. SG-LEM simulations of the MRB case demonstrate the method’s sensitivity to clustering parameters, with flow-aligned clusters significantly improving flame stability. LEM domains on the super-grid were able to represent the MRB flame topology while LES radial profiles including velocity, mixture fraction, temperature, and $${\textrm{CO}}$$ CO mass fraction, were validated against experimental data and also reference simulations using standard combustion closures. The work also investigates discrepancies in CO profiles using conditional statistics and stand-alone LEM simulations. Finally, the work identifies areas of improvement for the SG-LEM framework, in particular relating to cluster generation, and (advective and diffusive) mass exchange between neighbouring LEM domains, as well as possible solutions for future SG-LEM implementations which could improve the model’s predictive capability. Y1 - 2024 U6 - https://doi.org/10.1007/s10494-024-00602-x SN - 1386-6184 VL - 2024 PB - Springer Science and Business Media LLC ER - TY - GEN A1 - Klein, Rupert A1 - Nadolski, Maikel A1 - Zenker, Christian A1 - Oevermann, Michael A1 - Paschereit, Christian Oliver T1 - Pressure gain combustion for gas turbines : analysis of a fully coupled engine model T2 - Journal of Engineering for Gas Turbines and Power N2 - The “Shockless Explosion Combustion” (SEC) concept for gas turbine combustors, introduced in 2014, approximates constant volume combustion (CVC) by harnessing acoustic confinement of auto-igniting gas packets. The resulting pressure waves simultaneously transmit combustion energy to a turbine plenum and facilitate the combustor's recharging against an average pressure gain. Challenges in actualizing an SEC-driven gas turbine include (i) the creation of charge stratifications for nearly homogeneous auto-ignition, (ii) protecting the turbocomponents from combustion-induced pressure fluctuations, (iii) providing evidence that efficiency gains comparable to those of CVC over deflagrative combustion can be realized, and (iv) designing an effective one-way intake valve. This work addresses challenges (i)–(iii) utilizing computational engine models incorporating a quasi-one-dimensional combustor, zero- and two-dimensional (2D) compressor and turbine plena, and quasi-stationary turbocomponents. Two SEC operational modes are identified which fire at roughly one and two times the combustors' acoustic frequencies. Results for SEC-driven gas turbines with compressor pressure ratios of 6:1 and 20:1 reveal 1.5-fold mean pressure gains across the combustors. Assuming ideally efficient compressors and turbines, efficiency gains over engines with deflagration-based combustors of 30% and 18% are realized, respectively. With absolute values of 52% and 66%, the obtained efficiencies are close to the theoretical Humphrey cycle efficiencies of 54% and 65% for the mentioned precompression ratios. Detailed thermodynamic cycle analyses for individual gas parcels suggest that there is room for further efficiency gains through optimized plenum and combustor designs. Y1 - 2024 U6 - https://doi.org/10.1115/1.4066348 SN - 0742-4795 VL - 147 IS - 2 PB - ASME International ER - TY - GEN A1 - Movaghar, Amirreza A1 - Chiodi, Robert A1 - Oevermann, Michael A1 - Desjardins, Olivier A1 - Kerstein, Alan T1 - Assessment of a multiphase formulation of one-dimensional turbulence using direct numerical simulation of a decaying turbulent interfacial flow T2 - Physical Review Fluids N2 - The interaction between turbulence and surface tension is studied numerically using the one-dimensional-turbulence (ODT) model. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps that represent the effects of individual turbulent eddies on property fields. It provides affordable high resolution of interface creation and property gradients within each phase, which are key for capturing the local behavior as well as overall trends, and has been shown to reproduce the main features of an experimentally determined regime diagram for primary jet breakup. Here ODT is used to investigate the interaction of turbulence with an initially planar interface. The notional flat interface is inserted into a periodic box of decaying homogeneous isotropic turbulence, simulated for a variety of turbulent Reynolds and Weber numbers. Unity density and viscosity ratios serve to focus solely on the interaction between fluid inertia and the surface-tension force. Statistical measures of interface surface density and spatial structure along the direction normal to the initial surface are compared to corresponding direct-numerical-simulation (DNS) data. Allowing the origin of the lateral coordinate system to follow the location of the median interface element improves the agreement between ODT and DNS, reflecting the absence of lateral nonvortical displacements in ODT. Beyond the DNS-accessible regime, ODT is shown to obey the predicted parameter dependencies of the Kolmogorov critical scale in both the inertial and dissipative turbulent-cascade subranges. Notably, the probability density function of local fluctuations of the critical scale is found to collapse to a universal curve across both subranges. Published by the American Physical Society 2024 Y1 - 2024 U6 - https://doi.org/10.1103/PhysRevFluids.9.104003 SN - 2469-990X VL - 9 IS - 10 PB - American Physical Society (APS) ER - TY - GEN A1 - Menon, Abhilash M. A1 - Oevermann, Michael A1 - Kerstein, Alan R. T1 - A super-grid approach for LES combustion closure using the linear eddy model T2 - Combustion Theory and Modelling N2 - LES–LEM is a simulation approach for turbulent combustion in which the stochastic Linear Eddy Model (LEM) is used for sub-grid mixing and combustion closure in Large-Eddy Simulation (LES). LEM resolves, along a one-dimensional line, all spatial and temporal scales, provides on-the-fly local turbulent flame statistics, captures finite rate chemistry effects and directly incorporates turbulence-chemistry interaction. However, the approach is computationally expensive as it requires advancing an LEM-line in each LES cell. This paper introduces a novel turbulent combustion closure model for LES using LEM to address this issue. It involves coarse-graining the LES mesh to generate a coarse- level ‘super-grid’ comprised of cell-clusters. Each cell-cluster, instead of each LES cell, then contains a single LEM domain. This domain advances the combined advection–reaction–diffusion solution and also provides suitably conditioned statistics for thermochemical scalars such as species mass fractions. Local LES-filtered thermochemical states are then obtained by probability-density-function (PDF) weighted integration of binned conditionally averaged scalars, akin to standard presumed PDF approaches for reactive LES but with physics-based determination of the full thermochemical state for particular values of the conditioning variables. The proposed method is termed ‘super-grid LEM’ or ‘SG-LEM’. The paper describes LEM reaction–diffusion advancement, the LEM representation of turbulent advection, a novel splicing algorithm (a key feature of LES–LEM) formulated for the super-grid approach, a wall treatment, and a thermochemical LES closure procedure. To validate the proposed model, a pressure-based solver was developed using the OpenFOAM library and tested on a premixed ethylene flame stabilised over a backward facing step, a setup for which some DNS data is available. SG-LEM provides high resolution flame structures, temperature and mass fractions suitable for LES thermochemical closure. Additionally, it provides reaction-rate data at the coarse level, a unique feature compared to other mapping-type closure methods. Quantitative comparisons are made between the proposed model and time-averaged DNS data, focussing on velocity, temperature and species mass fraction. Results show good agreement downstream of the step. Furthermore, comparison with an equivalent Partially-Stirred Reactor (PaSR) simulation demonstrates the superior predictive capability of SG-LEM. Additionally, the paper briefly examines the sensitivity of the model to coarse-graining parameters and finally, explores computational efficiency highlighting the substantial speedup achieved when compared to the standard LES–LEM approach with potentially significant speedup relative to PaSR closure for the intensely turbulent regimes of principal interest. KW - LES KW - LEM KW - Combustion closure KW - Presumed PDFs KW - Splicing Y1 - 2023 U6 - https://doi.org/10.1080/13647830.2023.2260351 SN - 1364-7830 VL - 28 IS - 1 SP - 99 EP - 126 PB - Informa UK Limited ER - TY - JOUR A1 - Doubiani, Nidal A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A pressure-coupled Representative Interactive Linear Eddy Model (RILEM) for engine simulations JF - Fuel N2 - The Representative Linear Eddy Model (RILEM) was introduced by Lackmann et al. (2018) as an alternative modeling approach to simulate turbulent non-premixed combustion in engines. The model utilizes a RANS approach for turbulence and the Linear Eddy Model (LEM) with a presumed probability density function (PDF) approach for combustion closure. A distinct feature of RILEM is its potential to handle arbitrary combustion regimes and the consideration of complex physical phenomena such as differential diffusion effects. The original version of RILEM implemented a volume-based coupling between LEM and the flow solver. This work presents a new variant of RILEM, i.e., Multiple Representative Interactive Linear Eddy Model (MRILEM) based on a pressure-based coupling, to overcome some deficiencies of the original RILEM, namely statistical fidelity. Due to the introduced pressure coupling, the effects of heat losses (wall heat fluxes, latent heat of evaporation) on combustion are intrinsically included via the pressure trace. Furthermore, we introduce a new step function PDF for the progress variable defined by its mean value only. Issues with an incomplete solution space for mixture fraction and progress variable due to the stochastic nature of LEM are remedied with a PDF scaling technique, aided by a novel parameterization of the progress-variable PDF The new variant of RILEM is evaluated using part- and full-load cases of a heavy-duty metal engine. The impact of utilizing multiple LEM lines on the completeness of the solution space and its influence on the distribution of scalar values in the CFD domain was demonstrated. Results for pressure trace, flame structure, and CO emissions are analyzed and compared with simulations using the Multi-Zone Well-Mixed Model (MZWM) model and experiments. While pressure traces agree well among the different models and experiments, noteworthy differences are observed between the models regarding CO emissions and temperature. Effects of turbulence chemistry interaction were noticed when comparing MRILEM to the results of the MZWM simulation, namely flame brush and species mass fraction distribution. KW - Linear Eddy Model KW - Turbulence-chemistry interaction KW - Presumed PDF approach KW - Pollutant formation KW - Pressure coupling KW - Engine combustion Y1 - 2024 U6 - https://doi.org/10.1016/j.fuel.2023.129423 SN - 0016-2361 VL - 355 (2024) SP - 1 EP - 15 PB - Elsevier BV ER - TY - GEN A1 - Doubiani, Nidal A1 - Oevermann, Michael T1 - Multiple representative interactive linear eddy model: Investigation of turbulence chemistry interaction and evaluation of progress variable definition and PDFs T2 - Fuel N2 - Improving the predictions of unsteady effects in combustion processes requires novel combustion models that include turbulence chemistry interaction effects. The Multiple Representative Interactive Linear Eddy Model (MRILEM) is an improved version of the previous RILEM variant. MRILEM utilizes a pressure coupling instead of a volume constraint to intrinsically include heat effects into the LEM line with no supplementary modeling. In addition, it advances multiple LEM lines in parallel to improve statistical fidelity. The pressure coupling of MRILEM generates a coupling effect between the LEM lines that assists in communicating the combustion process between the lines. The ”Spray-B” engine of the Engine Combustion Network (ECN) was simulated using MRILEM. While the original RILEM variation employs a straightforward Dirac δ-peak for the progress variable, a realistic PDF requires this function to extend over the entire space. The introduced MRILEM compares the utilization of two progress variable PDFs, namely a step function defined based on the mean and a β-PDF generated from the progress variable mean and variance. The progress variable variance was calculated based on the Pierce and Moin formulation with a RANS adaptation based on the integral length scale. In addition, two definitions of the progress variable are investigated, namely O2 and h298. A tabulation method is introduced for RILEM to reduce the computational time by advancing pre-generated LEM solution matrices constructed in mixture fraction Z and progress variable c spaces. The different variants of the model, i.e., MRILEM-βZ-Stepc, MRILEM-βZ-βc, TRILEM-β-Stepc, and TRILEM-βZ-βc were compared against experiments based on heat release rate, ignition delay, flame lift-off, and computational time. KW - Linear eddy model KW - Turbulence chemistry interaction KW - Probability density function KW - Tabulation Y1 - 2025 U6 - https://doi.org/10.1016/j.fuel.2024.133445 SN - 0016-2361 VL - 381 SP - 1 EP - 15 PB - Elsevier BV ER - TY - GEN A1 - Doubiani, Nidal A1 - Oevermann, Michael A1 - Lucchini, Tommaso A1 - Zhou, Qiyan T1 - Numerical investigation of ducted fuel injection using Multiple Representative Interactive Linear Eddy Model T2 - International Journal of Engine Research N2 - Fuel-air mixing in non-premixed and partially premixed combustion has a major influence on soot emissions. Improving the mixing quality of the premixed region in non-premixed combustion upstream of the auto-ignition zone aids substantially in reducing soot emissions. The Ducted Fuel Injection (DFI) concept is based on injecting fuel inside a metal cylinder inside the combustion chamber at a certain distance from the injection nozzle exit hole. Although the concept is straightforward, recent studies have shown that implementing DFI in compression ignition combustion chambers dramatically affects soot mitigation. DFI improves air entrainment by a suction effect when fuel travels inside the duct, which increases the turbulence level at the inlet and enhances the fuel-air mixing quality. Additionally, DFI delays ignition by preventing the formation of stoichiometric regions at the spray cone’s outer region. This work utilizes a recently presented combustion model titled the Multiple Representative Interactive Linear Eddy Model (MRILEM) to simulate DFI in a high-pressure, high-temperature constant volume chamber. Several simulations are realized for two different ambient temperatures using an n-dodecane mechanism, where several parameters, such as ignition delay, lift-off length, and flame structure, are assessed. Simulation results are compared to experimental data from the literature and simulation results obtained with the Multi-Zone Well Mixed (MZWM) model simulation results. Results show that by enforcing the duct on the LEM line and modifying the turbulence implementation strategy, MRILEM shows overall realistic predictions for DFI cases and reasonable quantitative results for lift-off length and ignition delay compared to the MZWM model. Y1 - 2024 U6 - https://doi.org/10.1177/14680874241298046 SN - 1468-0874 VL - 2025 PB - SAGE Publications ER - TY - GEN A1 - Özgünoğlu, Mehmet A1 - Mouokue, Gerard A1 - Oevermann, Michael A1 - Bensow, Rickard E. T1 - Numerical investigation of cavitation erosion in high-pressure fuel injector in the presence of surface deviations T2 - Fuel N2 - This study investigates cavitation-induced erosion in high-pressure fuel injectors using numerical simulations, focusing on the effects of surface deviations, turbulence modeling, and a refined approach for the erosion assessment. The proposed erosion model combines advanced erosion indicators to enhance predictive accuracy while addressing limitations in existing methodologies. Cavitation dynamics are simulated with the modified Zwart–Gerber–Belamri model, employing Reynolds-averaged Navier–Stokes (RANS) and Large Eddy Simulation (LES) approaches. Numerical results for a high-lift needle position are validated against experimental data, providing insights into erosion behavior in industrial heavy-duty injectors. Both Computer-Aided Design (CAD) and Tomography Scan (TS) models are used to evaluate the impact of surface deviations on erosion patterns. Results reveal that incorporating surface deviations reduces the vapor volume and alters the erosion patterns. LES simulations exhibit enhanced sensitivity to the surface deviations, capturing finer turbulence structures and local pressure fluctuations, whereas RANS provides reasonable accuracy with lower computational cost. KW - Fuel injector KW - CFD KW - Cavitation erosion KW - Surface deviations Y1 - 2025 U6 - https://doi.org/10.1016/j.fuel.2024.134174 SN - 0016-2361 VL - 386 SP - 1 EP - 21 PB - Elsevier BV ER - TY - GEN A1 - Menon, Abhilash M. A1 - Kerstein, Alan A1 - Oevermann, Michael T1 - Investigation of coarse-graining parameters for super-grid LEM closure applied to LES of practical bluff-body flames T2 - Combustion Theory and Modelling N2 - Large Eddy Simulation (LES) coupled with the Linear Eddy Model (LEM) provides a robust method for studying turbulent combustion, but it is computationally expensive due to the need for highly resolved sub-grid LEM domains. These domains simulate sub-grid stirring through stochastic rearrangements of scalar fields, while large-scale transport is modelled using a Lagrangian ‘splicing’ scheme. To address the computational cost of LES-LEM, a super-grid (SG) framework for LEM closure was developed by the authors (Comb. Theor. Model. 28, 2024), which uses coarse-graining, on-the-fly chemistry tabulation and a presumed PDF approach to reconstruct thermochemical fields at LES resolution. This study applies SG-LEM to a challenging setup, Case 1 of the Volvo Validation Rig, which involves a bluff-body-stabilised turbulent premixed propane-air flame, as a stress test to identify limitations that were not revealed by the previous application, in particular that of the coarse-graining parameters used to generate the super-grid. The intent is to yield a more realistically constrained assessment of the current capabilities of the method, and insight into possible ways for improving it. Four simulations were conducted using three SG cluster sizes. The finest resolution was tested with a global 2-step mechanism, showing good agreement with experimental data for temperature and velocity, particularly near the bluff body. The two larger cluster sizes used a 66-step skeletal mechanism for more detailed chemical closure but led to unphysical quenching due to splicing inaccuracies. To mitigate these issues, two novel additions were introduced: an intra-cluster-stirring routine and a method to control SG cluster shapes to reduce numerical dissipation. These methods improved flame stability with coarser SG clusters and more detailed mechanisms. Comparison with experiments showed good agreement for temperature and velocity, though elevated CO levels were observed in the recirculation region. Potential methods for further improving SG-LEM's capabilities are discussed. KW - LES-LEM KW - Premixed flames KW - Stabilised flames KW - Turbulence modelling KW - Subgrid-scale closure Y1 - 2024 U6 - https://doi.org/10.1080/13647830.2024.2428156 SN - 1364-7830 VL - 2024 SP - 1 EP - 22 PB - Taylor&Francis ER -