TY - GEN A1 - Sonia, G. A1 - Richter, E. A1 - Brunner, F. A1 - Denker, A. A1 - Lossy, R. A1 - Lenk, Friedrich A1 - Opitz-Coutureau, J. A1 - Mai, M. A1 - Schmidt, J. A1 - Zeimer, U. A1 - Wang, L. A1 - Baskar, K. A1 - Weyers, M. A1 - Würfl, Joachim A1 - Tränkle, Günther T1 - High energy irradiation effects on AlGaN/GaN HFET devices T2 - Semiconductor Science and Technology N2 - The effect of proton, carbon, oxygen and krypton irradiation on AlGaN HFET devices has been studied. Irradiation was performed at 68 and 120 MeV with fluences in the range from 1 × 10^7 to 1 × 10^13 cm2 . Before and after irradiation, dc and pulsed I – V characteristics, loadpull and S -parameters of the AlGaN HFET devices were measured. A thick GaN reference layer was characterized by x-ray diffraction, photoluminescence and Hall measurements before and after irradiation. Proton, carbon and oxygen irradiation show no degradation in devices while krypton irradiation shows a small change at a fluence of 1 × 10 10 cm2 in the device characteristics. The device results are correlated with the thick GaN results. Y1 - 2007 U6 - https://doi.org/10.1088/0268-1242/22/11/007 SN - 0268-1242 VL - 22 IS - 11 SP - 1220 EP - 1224 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 - CHAP A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - ODTLES: Mulitscale turbulence modeling and buoyant application T2 - Book of abstracts, 7th European Postgraduate Fluid Dynamics Conference, Ilmenau, Germany, 14th - 17th, July 2014 Y1 - 2014 CY - Ilmenau ER - TY - GEN A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Lyra, Sgouria A1 - Kolla, Hemanth A1 - Chen, Jackie H. T1 - One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS T2 - Combustion and Flame Y1 - 2014 SN - 1556-2921 VL - 162 IS - 8 SP - 2999 EP - 3015 ER - TY - GEN A1 - Schmidt, Heiko A1 - Glawe, Christoph A1 - Jozefik, Zoltan A1 - Meiselbach, Falko T. A1 - Kerstein, Alan R. T1 - On the benefits of ODT-based stochastic turbulence modeling T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - We summarize the group’s progress in applying, analyzing, and improving ODT and ODT-based stochastic turbulence models like ODTLES. Compared to DNS these models span a wider range of scales while compared to RANS/LES (i) the molecular effects are retained and (ii) no assumption of scale separation is made. In this regard ODTLES has more properties of DNS than of standard LES. Y1 - 2014 SN - 1617-7061 VL - 14 IS - 1 SP - 655 EP - 656 ER - TY - CHAP A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko ED - King, Rudibert T1 - Towards a compressible reactive multiscale approach based on One-Dimensional Turbulence T2 - Active Flow and Combustion Control 2014 N2 - Due to its huge complexity, progress in understanding and prediction of turbulent combustion is extremely challenging. In principle, progress is possible without improved understanding through direct numerical solution (DNS) of the exact governing equations, but the wide range of spatial and temporal scales often renders it unaffordable, so coarse-grained 3D numerical simulations with subgrid parameterization of the unresolved scales are often used. This is especially problematic for multi-physics regimes such as reacting flows because much of the complexity is thus relegated to the unresolved small scales. One-Dimensional Turbulence (ODT) is an alternative stochastic model for turbulent flow simulation. It operates on a 1D spatial domain via time advancing individual flow realizations rather than ensemble-averaged quantities. The lack of spatial and temporal filtering on this 1D domain enables a physically sound multiscale treatment which is especially useful for combustion applications where, e.g., sharp interfaces or small chemical time scales have to be resolved. Lignell et al. recently introduced an efficient ODT implementation using an adaptive mesh. As all existing ODT versions it operates in the incompressible regime and thus cannot handle compressibility effects and their interactions with turbulence and chemistry which complicate the physical picture even further. In this paper we make a first step toward an extension of the ODT methodology towards an efficient compressible implementation. The necessary algorithmic changes are highlighted and preliminary results for a standard non-reactive shock tube problem as well as for a turbulent reactive case illustrate the potential of the extended approach. Y1 - 2014 SN - 978-3-319-11967-0 SN - 978-3-319-11966-3 SP - 197 EP - 211 PB - Springer CY - Switzerland ER - TY - CHAP A1 - Stollberg, Christian A1 - Schmidt, M. A1 - Namango, Saul A1 - Pohl, R. A1 - Ay, Peter T1 - Conditioning, Identification and Automatic Sorting of Plastic Automotive Parts for Productive Recycling T2 - International Automobile Recycling Congress, IARC 2002, Geneva, Switzerland, March 13 - 15, 2002, proceedings KW - automobile recycling Y1 - 2002 PB - ICM AG CY - Muri ER - TY - CHAP A1 - Stollberg, Christian A1 - Namango, Saul A1 - Schmidt, M. A1 - Pohl, R. A1 - Ay, Peter T1 - Preparation of plastics for automatic identification as the first step in recycling of automotive parts T2 - Proceedings of the XXII International Mineral Processing Congress, Cape Town, South Africa, 29 September - 3 October 2003 KW - automobile recycling Y1 - 2003 PB - South African Institute of Mining & Meta CY - Marshalltown, South Africa ER - TY - GEN A1 - Jahn, Stephan F. A1 - Blaudeck, Thomas A1 - Baumann, Reinhard R. A1 - Jakob, Alexander A1 - Ecorchard, Petra A1 - Rüffer, Tobias A1 - Lang, Heinrich A1 - Schmidt, Peer T1 - Inkjet Printing of Conductive Silver Patterns by Using the First Aqueous Particle-Free MOD Ink without Additional Stabilizing Ligands T2 - Chemistry of Materials N2 - The chemical and physical properties of [AgO2C(CH2OCH2)3H] (3) and its use as an aqueous, ligand-free MOD ink (MOD = metal−organic decomposition) for piezo inkjet printing is discussed. The printed, thermal, or photochemical sintered silver features are electrically conductive on glass (2.7 × 107 S m−1) and PET (PET = polyethylene terephthalate) substrates (1.1 × 107 S m−1) corresponding to 43% and 18% of the bulk silver conductivity. Conducted tape tests show the suitability of the ink for particularly polymer substrates. TG-MS studies demonstrate a two-step decomposition for the conversion of 3 to elemental silver. The structure of 3 in the solid state was determined by single X-ray structure determination. Y1 - 2010 UR - http://pubs.acs.org/doi/abs/10.1021/cm9036428 U6 - https://doi.org/10.1021/cm9036428 SN - 1520-5002 VL - 22 IS - 10 SP - 3067 EP - 3071 ER - TY - GEN A1 - Jahn, Stephan F. A1 - Jakob, Alexander A1 - Blaudeck, Thomas A1 - Schmidt, Peer A1 - Lang, Heinrich A1 - Baumann, Reinhard R. T1 - Inkjet printing of conductive patterns with an aqueous solution of [AgO2C(CH2OCH2)3H] without any additional stabilizing ligands T2 - Thin Solid Films N2 - The use of silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate, [AgO2C(CH2OCH2)3H], and its application as an aqueous metal-organic decomposition (MOD) inkjet ink is reported. The chemical and physical properties of the silver carboxylate and the ink formulated thereof are discussed. The ink meets all requirements of piezo driven inkjet printing. The printed features were converted into electrically conducting silver patterns by thermal or photo-thermal treatment. The conversion of [AgO2C(CH2OCH2)3H] to elemental silver follows a two-step decomposition as demonstrated by thermogravimetry–mass spectrometry (TG–MS) measurements. The measured conductivities of the printed features on glass and polyethylene-terephthalate (PET) are 2.7 × 107 S m−1 and 1.1 × 107 S m−1, respectively, which correspond to 43% (glass) and 18% (PET) of the bulk silver conductivity. KW - Inkjet printing KW - Silver KW - Carboxylate KW - Ethyleneglycol KW - Flexible electronics Y1 - 2010 UR - http://www.sciencedirect.com/science/article/pii/S0040609010000866 U6 - https://doi.org/10.1016/j.tsf.2010.01.030 SN - 0040-6090 VL - 518 IS - 12 SP - 3218 EP - 3222 ER - TY - CHAP A1 - Bleh, D. A1 - Ostendorf, Ralf A1 - Merten, A. A1 - Grahmann, Jan A1 - Schenk, Harald A1 - Kunzer, M. A1 - Schmidt, R. A1 - Wagner, J. T1 - Miniaturization of a fast tunable external cavity QCL with customized gratings and MOEMS components T2 - International Quantum Cascade Lasers School & Workshop (IQCLSW), Policoro, Italy Y1 - 2014 UR - http://www.iqclsw2014.cnr.it/wp-content/uploads/2014/03/Bleh-IQCLSW2014.pdf?0f100a SP - 1 EP - 2 ER - TY - CHAP A1 - Glawe, Christoph A1 - Schulz, Falko T. A1 - Gonzalez-Juez, Esteban D. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - ODTLES Simulations of Turbulent Flows through Heated Channels and Ducts T2 - 8th International Symposium on turbulence and shear flow phenomena (TSFP8), 28–30 August 2013, Poitiers, France, vol. 2 N2 - A widely occurring problem in fluid dynamics either in engineering or e.g. hydrology is the turbulent transport through channels and ducts. ODTLES, a stochastic based multi-scale and multi-dimensional model, is a promising tool to describe these flows even including scalar proper- ties like temperature. We are quantifying the ability of ODTLES to describe the heated channel flow with respect to the Prandtl number and the flow through squared ducts with respect to the Reynolds number. Y1 - 2013 UR - http://www.tsfp-conference.org/proceedings/2013/v2/htc.pdf SP - 1 EP - 6 ER - TY - GEN A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Lyra, Sgouria A1 - Kolla, Hemanth A1 - Chen, Jackie H. T1 - One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS T2 - Combustion and Flame N2 - The one-dimensional turbulence (ODT) model is applied to a reactant-to-product counterflow configuration and results are compared with DNS data. The model employed herein solves conservation equations for momentum, energy, and species on a one dimensional (1D) domain corresponding to the line spanning the domain between nozzle orifice centers. The effects of turbulent mixing are modeled via a stochastic process, while the Kolmogorov and reactive length and time scales are explicitly resolved and a detailed chemical kinetic mechanism is used. Comparisons between model and DNS results for spatial mean and root-mean-square (RMS) velocity, temperature, and major and minor species profiles are shown. The ODT approach shows qualitatively and quantitatively reasonable agreement with the DNS data. Scatter plots and statistics conditioned on temperature are also compared for heat release rate and all species. ODT is able to capture the range of results depicted by DNS. However, conditional statistics show signs of underignition. Y1 - 2015 U6 - https://doi.org/10.1016/j.combustflame.2015.05.010 SN - 0010-2180 VL - 162 IS - 8 SP - 2999 EP - 3015 ER - TY - GEN A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Simulation of shock–turbulence interaction in non-reactive flow and in turbulent deflagration and detonation regimes using one-dimensional turbulence T2 - Combustion and Flame N2 - The one-dimensional turbulence (ODT) methodology is extended to include an efficient compressible implementation and a model for capturing shock-induced turbulence is presented. Lignell et al. recently introduced a Lagrangian ODT implementation using an adaptive mesh. As the code operates in the incompressible regime (apart from constant-pressure dilatation) it cannot handle compressibility effects and their interactions with turbulence and chemistry. The necessary algorithmic changes to include compressibility effects are highlighted and our model for capturing shock- turbulence interaction is presented. To validate our compressible solver, we compare results for the Sod shock tube problem against a finite volume Riemannsolver. To validate our model for shock–turbulence interaction, we present comparisons for a non-reactive and a reactive case. First, results of a shock traveling from light (air) to heavy (SF6) with recheck have been simulated to match mixing width growth data of experiments and turbulent kinetic energy results from LES.Then, for one-step chemistry calibrated to represent an acetylene/airmixture we simulate the interaction of a shock wave with an expanding flame front, and compare results with 2D simulation (2D-sim) data for flame brush formation and ensuing deflagration-to-detonation transitions (DDT). Results for the Sod shock tube comparison show that the shock speed and profile are captured accurately. Results for the non-reactive shock–recheck problem show that interface growth at all simulated Mach numbers is captured accurately and that the turbulent kinetic energy agrees in order of magnitude with LES data. The reactive shock tube results show that the flame brush thickness compares well to 2D-sim data and that the approximate location and timing of the DDT can be captured. The known sensitivity of DDT characteristics to details of individual flow realizations, seen also in ODT, implies that model agreement can be quantified only by comparing flow ensembles, which are presently unavailable other than in an ODT run-to-run sensitivity study that is reported herein. Y1 - 2016 U6 - https://doi.org/10.1016/j.combustflame.2015.10.035 SN - 0010-2180 VL - 164 SP - 53 EP - 67 ER - TY - GEN A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Klein, Rupert T1 - XLES Part I: Introduction to Extended Large Eddy Simulation T2 - arXiv.org N2 - Direct numerical simulation (DNS), mostly used in fundamental turbulence research, is limited to low turbulent intensities due the current and future computer resources. Standard turbulence models, like RaNS (Reynolds averaged Navier-Stokes) and LES (Large Eddy Simulation), are applied to flows in engineering, but they miss small scale effects, which are frequently of importance, see e.g. the whole area of reactive flows, flows with apparent Prandtl or Schmidt number effects, or even wall bounded flows. A recent alternative to these standard approaches is the one-dimensional turbulence (ODT) model, which is limited to 1D sub-domains. In two papers we will provide a generalized filter strategy, called XLES (extended LES), including a formal theory (part I) and one special approach in the XLES family of models, called ODTLES (in part II (see Glawe et al. (2015))). ODTLES uses an ODT sub-grid model to describe all turbulent scales not represented by XLES, which leaves the larger scales to be simulated in 3D. This allows a turbulence modeling approach with a 3D resolution mainly independent of the turbulent intensity. Thus ODTLES is able to compute highly turbulent flows in domains of moderate complexity affordably and including the full range of turbulent and diffusive scales. The convergence of XLES to DNS is shown and the unconventional XLES advection approach is investigated in basic numerical tests. In part II, highly turbulent channel and duct flow results are discussed and show the future potential of XLES and ODTLES. Y1 - 2015 UR - http://arxiv.org/abs/1506.04930 ER - TY - GEN A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Klein, Rupert T1 - XLES Part II: From Extended Large Eddy Simulation to ODTLES T2 - arXiv.org N2 - In turbulence research and flow applications, turbulence models like RaNS (Reynolds averaged Navier-Stokes) models and LES (Large Eddy Simulation) are used. Both models filter the governing flow equations. Thus a scale separation approach is introduced for modeling purposes with the large scales simulated using a numerical scheme while smaller scales are assumed to be less important and might be modeled more or less easily. Unfortunately small scales are frequently of big importance, e.g. in reactive flows, wall bounded flows, or flows with significant Prandtl or Schmidt number effects. Recent alternatives to these standard models are the class of models based on the one-dimensional turbulence (ODT) idea, like ODTLES. The ability of ODT to capture highly turbulent flows (recently up to Reτ=6×105) allows ODTLES to realize 3D resolutions basically independent of the turbulent intensity. In two papers we provide a formal theory and application of an innovative modeling strategy for highly turbulent flows in domains of moderate complexity: In part I (see Glawe et al. (2015)) a new general filtering approach, called XLES (extended LES), is introduced. Contrary to LES, XLES is based on 2D filtering of the governing equations, whereby additional small scale terms are interpreted numerically. In this work a new ansatz for the ODTLES model is introduced as one special approach in the XLES family of models by incorporating the ODT model into XLES. The ODT model introduces microstructures not captured by the XLES filtered equations. To illustrate the ODTLES model capabilities, turbulent channel and duct flows up to friction Reynolds number Reτ=10000 are studied. Y1 - 2015 UR - http://arxiv.org/abs/1506.04938 ER - TY - CHAP A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - ODTLES: A Multi-scale Ansatz for highly turbulent flows T2 - 15 The European turbulence conference, 25-28 august, 2015, Delft, The Netherland N2 - We use ODTLES, a multi-dimensional extension of the One-Dimensional-Turbulence model (ODT). ODT describes turbulent advection on a 1D sub-domain using a stochastic process for turbulent advection. These 1D sub-domains are coupled to obtain a 3D approach. ODTLES is applied to channel flow. Preliminary results for the pdf of the wall shear stress are compared to DNS. Y1 - 2015 UR - http://www.etc15.nl/proceedings/proceedings/documents/431.pdf ER - TY - CHAP A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Incorporation of acceleration effects into the One-dimensional-turbulence model, with application to turbulent combustion and shock-turbulence interactions T2 - 15th European Turbulence Conference 2015 August 25-28th, 2015, Delft, The Netherlands N2 - One-dimensional turbulence (ODT) is a stochastic simulation in which 3D turbulence effects are captured on a notional 1D line of sight by introducing instantaneous spatial rearrangements (maps) that represent advection by notional turbulent eddies. These eddy events incorporate the possibility of kinetic-energy changes that are equal and opposite to changes of other forms of energy such as the gravitational potential energy change due to a rearrangement of a vertical density profile. This illustrates that motion aligned with an applied force, in this case gravitation g, can be associated with energy change. Using this principle, we 1) present a model of turbulence interaction with the dilatational acceleration caused by thermal expansion in flames and show results for a turbulent counterflow flame with comparison to DNS and 2) present a model for shock-induced turbulence and show results for mixing width growth in a shock tube with comparison to experiments. Y1 - 2015 UR - http://www.etc15.nl/proceedings/proceedings/documents/356.pdf ER - TY - GEN A1 - Chun, K. R. Julian A1 - Schmidt, Boris A1 - Kuck, Karl-Heinz A1 - Andresen, Dietrich A1 - Willems, Stefan A1 - Spitzer, Stefan G. A1 - Hoffmann, Ellen A1 - Schumacher, Burghard A1 - Eckardt, Lars A1 - Seidl, Karlheinz A1 - Jünger, Claus A1 - Horack, Martin A1 - Brachmann, Johannes A1 - Senges, Jochen T1 - Catheter ablation of atrial fibrillation in the young T2 - Clinical Research in Cardiology Y1 - 2013 U6 - https://doi.org/10.1007/s00392-013-0553-6 SN - 1861-0684 SN - 1861-0692 VL - 102 IS - 6 SP - 459 EP - 468 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 - Efimova, Anastasia A1 - Varga, Janos A1 - Matuschek, Georg A1 - Saraji-Bozorgzad, Mohammad R. A1 - Denner, Thomas A1 - Zimmermann, Ralf A1 - Schmidt, Peer T1 - Thermal Resilience of Imidazolium-Based Ionic Liquids—Studies on Short- and Long-Term Thermal Stability and Decomposition Mechanism of 1-Alkyl-3-methylimidazolium Halides by Thermal Analysis and Single-Photon Ionization Time-of-Flight Mass Spectrometry T2 - Journal of Physical Chemistry B N2 - Ionic liquids are often considered as green alternatives of volatile organic solvents. The thermal behavior of the ionic liquids is relevant for a number of emerging large-scale applications at elevated temperature. Knowledge about the degradation products is indispensable for treatment and recycling of the used ionic liquids. The objective of this paper was an investigation of the short- and long-term stability of several 1-alkyl-3-methylimidazolium halides, determination of the degradation products, and the elucidation of their decomposition patterns and structure–stability relations. Short-term stability and mechanism of thermal degradation were investigated by a self-developed, innovative thermal analysis single-photon ionization time-of-flight mass spectrometry device with Skimmer coupling. The applied technology provides real-time monitoring of the forming species and allows tracing their change during the course of the decomposition. Therein, the almost fragment-free soft ionization with vacuum ultraviolet photons plays a crucial role. We have detected unfragmented molecules whose formation was only assumed by electron ionization. Nevertheless, the main decomposition products of the selected ionic liquids were alkyl imidazoles, alkenes, alkyl halides, and hydrogen halides. From the decomposition products, we have deduced the fragmentation patterns and discussed their interrelation with the length of the alkyl chain and the type of the halide anion. Our results did not suggest the evaporation of the investigated ionic liquids prior to their decomposition under atmospheric conditions. Long-term thermal stability and applicability were determined based on thermogravimetric analysis evaluated with a kinetic model. Thus, the time-dependent maximum operation temperature (MOT) for the respective ionic liquids has been calculated. As a rule, the short-term stability overestimates the long-term decomposition temperatures; the calculated MOT are significantly lower (at least 100 K) than the standardly obtained decomposition temperatures. KW - Ionic liquid KW - Thermal analysis KW - Thermal decomposition KW - Maximum operation temperature Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcb.8b06416 VL - 122 IS - 37 SP - 8738 EP - 8749 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 - Klein, Marten A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Stochastic modeling of transient boundary layers in high-Rayleigh-number thermal convection T2 - 25th International Congress of Theoretical and Applied Mechanics (ICTAM 20+1) N2 - One-dimensional turbulence (ODT) modeling is used to investigate the boundary layer in high-Rayleigh-number thermal convection for a notionally infinite horizontal layer of fluid. The model formulation distinguishes between turbulent advection, which is modeled by a stochastic process, and deterministic molecular diffusion to capture relevant vertical transport processes (including counter-gradient fluxes). For this study, statistical homogenization is applied to the two horizontal dimensions so that we use ODT as stand-alone tool. We show that the model yields mean and fluctuation temperature profiles that are in several respects consistent with available reference data. Furthermore, the profile of a surrogate for the fluctuation velocity is reminiscent of canonical wall turbulence. KW - one-dimensional turbulence KW - thermal convection KW - turbulent boundary layer Y1 - 2020 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_2020_ODT-RBC_ICTAM20+1.pdf ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Transition to the ultimate regime in a stochastic model for thermal convection with internal sources Y1 - 2021 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_ipam21.pdf CY - IPAM Workshop: Transport and Mixing in Complex and Turbulent Flows (CTF2021), University of California, Los Angeles, CA, USA ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Transition to the ultimate regime in a stochastic model for radiatively driven turbulent convection T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft - BPCPPDYSOE21 KW - stochastic turbulence modeling KW - turbulent thermal convection KW - one-dimensional turbulence KW - heat transfer Y1 - 2021 UR - https://www.dpg-verhandlungen.de/year/2021/conference/bpcppdysoe/part/dy/session/2/contribution/1?lang=en ER -