@misc{MoeckOevermannKleinetal., author = {Moeck, Jonas Pablo and Oevermann, Michael and Klein, Rupert and Paschereit, Christian Oliver and Schmidt, Heiko}, title = {A two-way coupling for modeling thermoacoustic instabilities in a flat flame Rijke tube}, series = {Proceedings of the Combustion Institute}, volume = {32}, journal = {Proceedings of the Combustion Institute}, number = {1}, issn = {1540-7489}, doi = {10.1016/j.proci.2008.05.062}, pages = {1199 -- 1207}, language = {en} } @incollection{SchmidtKlein, author = {Schmidt, Heiko and Klein, Rupert}, title = {Flexible flame structure modelling in a Flame Front Tracking Scheme}, series = {Analysis and Numerics for Conservation Laws}, booktitle = {Analysis and Numerics for Conservation Laws}, editor = {Warnecke, Gerald}, publisher = {Springer}, address = {Heidelberg}, isbn = {978-3-540-24834-7}, pages = {405 -- 427}, language = {en} } @misc{SchmidtKlein, author = {Schmidt, Heiko and Klein, Rupert}, title = {A generalized level-set/in-cell-reconstruction approach for accelerating turbulent premixed flames}, series = {Combustion Theory and Modelling}, volume = {7}, journal = {Combustion Theory and Modelling}, number = {2}, issn = {1364-7830}, doi = {10.1088/1364-7830/7/2/303}, pages = {243 -- 267}, abstract = {An extended numerical technique for the simulation of accelerating turbulent premixed flames in large scale geometries is presented. It is based on a hybrid capturing tracking technique. It resembles a tracking scheme in that the front geometry is explicitly computed using a level-set method. The basic flow properties are provided by solving the compressible flow equations. The flame-flow-coupling is achieved by an in-cell-reconstruction technique. In cells cut by the flame, the discontinuous solution is reconstructed from given cell averages by invoking explicitly some Rankine-Hugoniot type jump conditions. Then the reconstructed states and again the front geometry are used to define accurate effective numerical fluxes across grid cell interfaces intersected by the front during the time step considered. Hence, the scheme also resembles a capturing scheme in that only cell averages of conserved quantities are computed. To be able to model inherently unsteady effects, like quenching, reignition, etc, during flame acceleration, we modified the standard Rankine-Hugoniot jump conditions. A source term appearing in the\& modified jump conditions is computed by evaluating a suitable functional on the basis of a one-dimensional flame structure module, that is attached in the normal direction to the flame front. This module additionally yields quantities such as the net mass burning rate, necessary for the propagation of the level set, and the specific heat release important for the energy release due to the consumption of fuel. Generally, the flame structure calculation takes into account internal physical effects which are not active in the outer flow but essential for the front motion and its feedback on the surrounding fluid. If a suitable set of different (turbulent) combustion models to compute the flame structure is provided, the new numerical technique allows us to consistently represent laminar deflagrations, fast turbulent deflagrations as well as detonation waves. Supplemented with suitable criteria that capture the essence of a deflagration-to-detonation-transition (DDT), the complete evolution of such an event can be implemented in principle.}, language = {en} } @inproceedings{KersteinGlaweSchmidtetal., author = {Kerstein, Alan R. and Glawe, Christoph and Schmidt, Heiko and Klein, Rupert and Gonzalez-Juez, Esteban D. and Schmidt, Rodney}, title = {Computational modeling of scalar transport and buoyancy effects in turbulent flows using ODTLES}, series = {Bulletin of the American Physical Society}, volume = {57}, booktitle = {Bulletin of the American Physical Society}, number = {17}, language = {en} } @inproceedings{GlaweKleinKersteinetal., author = {Glawe, Christoph and Klein, Rupert and Kerstein, Alan R. and Schmidt, Heiko}, title = {Towards the simulation of gravity waves using the One-Dimensional Turbulence model}, series = {EGU General Assembly 2012, held 22-27 April, 2012 in Vienna}, booktitle = {EGU General Assembly 2012, held 22-27 April, 2012 in Vienna}, language = {en} } @misc{GlaweSchmidtKersteinetal., author = {Glawe, Christoph and Schmidt, Heiko and Kerstein, Alan R. and Klein, Rupert}, title = {XLES Part I: Introduction to Extended Large Eddy Simulation}, series = {arXiv.org}, journal = {arXiv.org}, pages = {38}, abstract = {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.}, language = {en} } @misc{GlaweSchmidtKersteinetal., author = {Glawe, Christoph and Schmidt, Heiko and Kerstein, Alan R. and Klein, Rupert}, title = {XLES Part II: From Extended Large Eddy Simulation to ODTLES}, series = {arXiv.org}, journal = {arXiv.org}, pages = {41}, abstract = {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.}, language = {en} } @misc{KleinNadolskiZenkeretal., author = {Klein, Rupert and Nadolski, Maikel and Zenker, Christian and Oevermann, Michael and Paschereit, Christian Oliver}, title = {Pressure gain combustion for gas turbines : analysis of a fully coupled engine model}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {147}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {2}, publisher = {ASME International}, issn = {0742-4795}, doi = {10.1115/1.4066348}, pages = {26}, abstract = {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.}, language = {en} }