Kempf A.M.,Imperial College London |
Geurts B.J.,University of Twente |
Geurts B.J.,TU Eindhoven |
Ma T.,Imperial College London |
And 2 more authors.
Journal of Scientific Computing | Year: 2011
Combustion LES requires modelling of physics beyond the flow-field only. These additional models lead to further quality issues and an even stronger need to quantify simulation and modelling errors. We illustrate stability problems, the need for consistent modelling in premixed and non-premixed combustion, and show how RANS models that have frequently been applied in an LES context can lead to strong conceptual errors. We outline the application of the error landscape approach to a complex non-premixed flame, and investigate several error indicators that have been developed for situations where no experimental reference data is available. © 2011 Springer Science+Business Media, LLC.
Knudsen E.,Stanford University |
Richardson E.S.,University of Southampton |
Doran E.M.,Robert Bosch GmbH |
Pitsch H.,Institute For Technische Verbrennung |
Chen J.H.,Combustion Research Facility
Physics of Fluids | Year: 2012
Scalar dissipation rates and subfilter scalar variances are important modeling parameters in large eddy simulations (LES) of reacting flows. Currently available models capture the general behavior of these parameters, but these models do not always perform with the degree of accuracy that is needed for predictive LES. Here, two direct numerical simulations (DNS) are used to analyze LES dissipation rate and variance modelsto propose a new model for the dissipation rate that is based on a transport equation. The first DNS that is considered is a non-premixed auto-igniting C2H4 jet flame simulation originally performed by Yoo et al. [Proc. Combust. Inst.33, 1619-1627 (2011)]10.1016/j.proci.2010.06.147. A LES of this case is run using algebraic models for the dissipation rate and subfilter variance. It is shown that the algebraic models fail to adequately reproduce the DNS results. This motivates the introduction of a transport equation model for the LES dissipation rate. Closure of the equation is addressed by formulating a new adapted dynamic approach. This approach borrows dynamically computed information from LES quantities that, unlike the dissipation rate, do not reside on the smallest flow length scales. The adapted dynamic approach is analyzed by considering a second DNS of scalar mixing in homogeneous isotropic turbulence. Data from this second DNS are used to confirm that the adapted dynamic approach successfully closes the dissipation rate equation over a wide range of LES filter widths. The first reacting jet case is then returned to and used to test the LES transport equation models. The transport equation model for the dissipation rate is shown to be more accurate than its algebraic counterpointthe dissipation rate is eliminated as a source of error in the transported variance model. © 2012 American Institute of Physics.
Won H.W.,Institute For Technische Verbrennung |
Peters N.,Institute For Technische Verbrennung
International Journal of Engine Research | Year: 2010
A combination of high-pressure injection and small orifices will be one of the strategies to achieve lean combustion. However, equispaced small orifices tend to increase soot under high-load condition because the spray tip penetration becomes exceedingly inadequate. For this reason, the cluster concept was chosen as a means to realize lean combustion. Six clusters were investigated with different injection pressures under part-load condition and high-load condition in a single-cylinder diesel engine, and the results were compared with a reference nozzle. The clusters tend to produce higher smoke than the reference nozzle for low injection pressures under conventional injection timing because the spray from the clusters with a shorter spray tip penetration loses momentum near the piston bowl. However, the clusters show improved smoke emissions with higher injection pressures. The combination of high-pressure injection and cluster concepts can be seen as one of the solutions to achieve lean combustion for diesel engines. Clusters with high-pressure injection have improved emissions, as better fuel atomization and evaporation are achieved while holding momentum near the piston bowl and maintaining the penetration of the spray. © 2010 IMechE.
Schaefer P.,Institute For Technische Verbrennung |
Gampert M.,Institute For Technische Verbrennung |
Hennig F.,Institute For Technische Verbrennung |
Peters N.,Institute For Technische Verbrennung
Notes on Numerical Fluid Mechanics and Multidisciplinary Design | Year: 2014
Streamlines constitute natural geometries in turbulent flows. In this work streamlines are segmented based on local extrema of the field of the absolute value of the velocity along the streamline coordinate. Streamline segments are parameterized based on their arclength and a theoretical scaling of the mean length with the geometric mean of the Kolmogorov length and the Taylor microscale is derived and found to be in good agreement with direct numerical simulations. © Springer International Publishing Switzerland 2014.