@inproceedings{JimenezJozefikSchmidt, author = {Jimenez, Carmen and Jozefik, Zoltan and Schmidt, Heiko}, title = {Detailed numerical simulation of forced planar premixed hydrocarbon flames}, series = {Conference on Modelling Fluid Flow (CMFF'12), September 4, 2012 - September 7, 2012}, booktitle = {Conference on Modelling Fluid Flow (CMFF'12), September 4, 2012 - September 7, 2012}, address = {Budapest}, language = {en} } @inproceedings{SchmidtJozefikJimenez, author = {Schmidt, Heiko and Jozefik, Zoltan and Jimenez, Carmen}, title = {Detailed numerical simulation of forced planar premixed flames}, series = {Book of abstracts, 34th International Symposium on Combustion, July 29 - August 3, Warsaw, Poland}, booktitle = {Book of abstracts, 34th International Symposium on Combustion, July 29 - August 3, Warsaw, Poland}, publisher = {The Combustion Institute, University of Technology}, address = {Warsaw}, language = {en} } @misc{SchmidtGlaweJozefiketal., author = {Schmidt, Heiko and Glawe, Christoph and Jozefik, Zoltan and Meiselbach, Falko T. and Kerstein, Alan R.}, title = {On the benefits of ODT-based stochastic turbulence modeling}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {14}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {1}, issn = {1617-7061}, pages = {655 -- 656}, abstract = {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.}, language = {en} } @incollection{JozefikKersteinSchmidt, author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko}, title = {Towards a compressible reactive multiscale approach based on One-Dimensional Turbulence}, series = {Active Flow and Combustion Control 2014}, booktitle = {Active Flow and Combustion Control 2014}, editor = {King, Rudibert}, publisher = {Springer}, address = {Switzerland}, isbn = {978-3-319-11967-0}, pages = {197 -- 211}, abstract = {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.}, language = {en} } @misc{JozefikKersteinSchmidtetal., author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko and Lyra, Sgouria and Kolla, Hemanth and Chen, Jackie H.}, title = {One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS}, series = {Combustion and Flame}, volume = {162}, journal = {Combustion and Flame}, number = {8}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2015.05.010}, pages = {2999 -- 3015}, abstract = {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.}, language = {en} } @misc{JozefikKersteinSchmidt, author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko}, title = {Simulation of shock-turbulence interaction in non-reactive flow and in turbulent deflagration and detonation regimes using one-dimensional turbulence}, series = {Combustion and Flame}, volume = {164}, journal = {Combustion and Flame}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2015.10.035}, pages = {53 -- 67}, abstract = {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.}, language = {en} } @misc{MonsonLignellFinneyetal., author = {Monson, Elizabeth I. and Lignell, David O. and Finney, Mark A. and Jozefik, Zoltan and Kerstein, Alan R. and Hintze, Ryan S.}, title = {Simulation of an ethylene wall fire using the spatially-evolving one-dimensional turbulence model}, series = {Fire Technology, Special Issue on Validation and Fire Modeling}, volume = {52}, journal = {Fire Technology, Special Issue on Validation and Fire Modeling}, number = {1}, issn = {1572-8099}, doi = {10.1007/s10694-014-0441-2}, pages = {176 -- 196}, language = {en} } @misc{StarickMedinaMendezKleinetal., author = {Starick, Tommy and Medina M{\´e}ndez, Juan Ali and Klein, Marten and Jozefik, Zoltan and Schmidt, Heiko}, title = {Zur j{\"u}ngsten Entwicklung in der Modellierung von turbulenten Verbrennungsprozessen mittels ODT}, series = {29. Deutscher Flammentag, 17-18 September 2019, Bochum, DE}, journal = {29. Deutscher Flammentag, 17-18 September 2019, Bochum, DE}, pages = {10}, abstract = {Die vorliegende Arbeit befasst sich mit den j{\"u}ngsten Entwicklungen und Anwendungen des One-Dimensional Turbulence (ODT) Modells auf reaktive Str{\"o}mungen. Bei ODT handelt es sich um ein stochastisches und abbildungsbasiertes Turbulenzmodell zur Simulation von turbulenten Str{\"o}mungen. In ODT wird das eindimensionale Rechengebiet als gedachte Linie durch das dreidimensionale Str{\"o}mungsfeld verstanden, welches in Richtung des mittleren Gradienten einer Geschwindigkeit oder anderer skalarer Felder orientiert ist. Die Besonderheit von ODT liegt in der Modellierung der turbulenten Advektion durch stochastisch auftretende Wirbelereignisse. Die molekulare Diffusion und Reaktionskinetik entlang des ODT-Rechengebietes wird mittels sich zeitlich entwickelnder, deterministischer Erhaltungsgleichungen ber{\"u}cksichtigt und vollst{\"a}ndig aufgel{\"o}st. In dieser Arbeit werden vorl{\"a}ufige ODT-Simulationsergebnisse von reaktiven Str{\"o}mungen f{\"u}r jeweilsein offenes und ein geschlossenes System vorgestellt. Essentielle Vorarbeiten, die die Vermischungeines passiven Skalars in einer planaren Strahld{\"u}se untersuchen, werden ebenfalls gezeigt. Beim offenen System handelt es sich um eine Methan/Luft Freistrahl-Flamme in einer umgebenden Str{\"o}mung aus heißen Verbrennungsgasen. Die Simulationsergebnisse werden zu Vergleichszweckenden Messungen von Cabra et al. gegen{\"u}bergestellt. Beim geschlossenen System wird die Selbstz{\"u}ndung von mageren n-Heptan Gemischen bei niedrigen Temperaturen und komplexer Reaktionskinetik betrachtet. Hierbei werden die ODT-Ergebnisse mit den Resultaten aus einer Direkten Numerischen Simulation (DNS) verglichen. In den durchgef{\"u}hrten Studien konnte gezeigt werden, dass die mittels ODT erzeugten Statistiken eine beachtlich gute {\"U}bereinstimmung mit den Vergleichsdaten aufweisen. Im Hinblick auf die reduzierte Dimensionalit{\"a}t von ODT, die Qualit{\"a}tder erzielten Ergebnisse und die erforderliche Rechenleistung, stellt ODT ein attraktives Modell zurSimulation von turbulenten und reaktiven Str{\"o}mungen dar.}, language = {de} } @misc{MedinaMendezSchmidtMaussetal., author = {Medina M{\´e}ndez, Juan Ali and Schmidt, Heiko and Mauß, Fabian and Jozefik, Zoltan}, title = {Constant volume n-Heptane autoignition using One-Dimensional Turbulence}, series = {Combustion and Flame}, volume = {190}, journal = {Combustion and Flame}, issn = {0010-2180}, doi = {10.1016/j.combustflame.2017.12.015}, pages = {388 -- 401}, abstract = {Abstract Constant volume premixed lean n-Heptane/air autoignition at high pressure is investigated using the One-Dimensional Turbulence (ODT) model. The configuration consists of a 1D fixed volume domain with a prescribed velocity spectrum and temperature fluctuations superimposed on an initial uniformly elevated scalar field. The sensitivity of the heat release rate and pressure evolution to the initial temperature distribution is studied by imposing different initial temperature fields while holding the mean, RMS and integral length scale of the field constant. Three detailed chemical mechanisms are employed for the prediction of autoignition and heat release rate. To mitigate the high computational cost associated with the calculation of the chemical source terms in the stiff complex mechanisms, an approach based on the Strang-Splitting method is presented. Finally, a …}, language = {en} } @inproceedings{CaviedesVoulliemeJozefikHinz, author = {Caviedes-Voulli{\`e}me, Daniel and Jozefik, Zoltan and Hinz, Christoph}, title = {Towards a physically-based multi-scale ecohydrological simulator for semi-arid regions}, series = {European Geosciences Union General Assembly 2017 Vienna, Austria, 23-28 April 2017}, booktitle = {European Geosciences Union General Assembly 2017 Vienna, Austria, 23-28 April 2017}, publisher = {European Geophysical Society}, address = {Katlenburg-Lindau}, abstract = {The use of numerical models as tools for describing and understanding complex ecohydrological systems has enabled to test hypothesis and propose fundamental, process-based explanations of the system system behaviour as a whole as well as its internal dynamics. Reaction-diffusion equations have been used to describe and generate organized pattern such as bands, spots, and labyrinths using simple feedback mechanisms and boundary conditions. Alternatively, pattern-matching cellular automaton models have been used to generate vegetation self-organization in arid and semi-arid regions also using simple description of surface hydrological processes. A key question is: How much physical realism is needed in order to adequately capture the pattern formation processes in semi-arid regions while reliably representing the water balance dynamics at the relevant time scales? In fact, redistribution of water by surface runoff at the hillslope scale occurs at temporal resolution of minutes while the vegetation development requires much lower temporal resolution and longer times spans. This generates a fundamental spatio-temporal multi-scale problem to be solved, for which high resolution rainfall and surface topography are required. Accordingly, the objective of this contribution is to provide proof-of-concept that governing processes can be described numerically at those multiple scales. The requirements for a simulating ecohydrological processes and pattern formation with increased physical realism are, amongst others: i. high resolution rainfall that adequately captures the triggers of growth as vegetation dynamics of arid regions respond as pulsed systems. ii. complex, natural topography in order to accurately model drainage patterns, as surface water redistribution is highly sensitive to topographic features. iii. microtopography and hydraulic roughness, as small scale variations do impact on large scale hillslope behaviour iv. moisture dependent infiltration as temporal dynamics of infiltration affects water storage under vegetation and in bare soil Despite the volume of research in this field, fundamental limitations still exist in the models regarding the aforementioned issues. Topography and hydrodynamics have been strongly simplified. Infiltration has been modelled as dependent on depth but independent of soil moisture. Temporal rainfall variability has only been addressed for seasonal rain. Spatial heterogenity of the topography as well as roughness and infiltration properties, has not been fully and explicitly represented. We hypothesize that physical processes must be robustly modelled and the drivers of complexity must be present with as much resolution as possible in order to provide the necessary realism to improve transient simulations, perhaps leading the way to virtual laboratories and, arguably, predictive tools. This work provides a first approach into a model with explicit hydrological processes represented by physicallybased hydrodynamic models, coupled with well-accepted vegetation models. The model aims to enable new possibilities relating to spatiotemporal variability, arbitrary topography and representation of spatial heterogeneity, including sub-daily (in fact, arbitrary) temporal variability of rain as the main forcing of the model, explicit representation of infiltration processes, and various feedback mechanisms between the hydrodynamics and the vegetation. Preliminary testing strongly suggests that the model is viable, has the potential of producing new information of internal dynamics of the system, and allows to successfully aggregate many of the sources of complexity. Initial benchmarking of the model also reveals strengths to be exploited, thus providing an interesting research outlook, as well as weaknesses to be addressed in the immediate future.}, language = {en} } @inproceedings{JozefikKersteinSchmidt, author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko}, title = {Incorporation of acceleration effects into the One-dimensional-turbulence model, with application to turbulent combustion and shock-turbulence interactions}, series = {15th European Turbulence Conference 2015 August 25-28th, 2015, Delft, The Netherlands}, booktitle = {15th European Turbulence Conference 2015 August 25-28th, 2015, Delft, The Netherlands}, pages = {2}, abstract = {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.}, language = {en} } @misc{StarickMedinaMendezKleinetal., author = {Starick, Tommy and Medina M{\´e}ndez, Juan Ali and Klein, Marten and Jozefik, Zoltan and Schmidt, Heiko}, title = {Zur j{\"u}ngsten Entwicklung in der Modellierung von turbulenten Verbrennungsprozessen mittels ODT}, pages = {1}, language = {de} } @misc{JozefikKersteinSchmidtetal., author = {Jozefik, Zoltan and Kerstein, Alan R. and Schmidt, Heiko and Lyra, Sgouria and Kolla, Hemanth and Chen, Jackie H.}, title = {One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS}, series = {Combustion and Flame}, volume = {162}, journal = {Combustion and Flame}, number = {8}, issn = {1556-2921}, pages = {2999 -- 3015}, language = {en} } @inproceedings{JozefikFrechenHinzetal., author = {Jozefik, Zoltan and Frechen, Tobias Nanu and Hinz, Christoph and Schmidt, Heiko}, title = {A cellular automata approach for modeling surface water runoff}, series = {European Geosciences Union, General Assembly 2015, Vienna, Austria, 13 April - 17 May 2015}, booktitle = {European Geosciences Union, General Assembly 2015, Vienna, Austria, 13 April - 17 May 2015}, publisher = {European Geophysical Society}, address = {Katlenburg-Lindau}, language = {en} }