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Realizable dynamic les of high reynolds number turbulent wall bounded flows

: Ahmadi, G.; Peinke, J.; Kassem, H.; Stoevesandt, B.; Mokhtarpoor, R.; Heinz, S.


Aerospace Research Central -ARC-; American Institute of Aeronautics and Astronautics -AIAA-, Washington/D.C.:
AIAA SciTech Forum 2019 : San Diego, California, 7-11 January 2019
Reston, Va.: AIAA, 2019
ISBN: 978-1-62410-578-4
19 S.
Science and Technology Forum and Exposition (SciTech Forum) <2019, San Diego/Calif.>
Fraunhofer IWES ()

The dynamic calculation of model coefficients in Large Eddy Simulation (LES) enables the flow to adjust to solid bounds without any need of explicit or empirical wall damping functions. Nevertheless, this approach can cause numerical instability specifically in the simulation of the flows with high Reynolds number. Meanwhile, stress-realizability is found to be connected to avoid numerical instability. One way to ensure the realizability of the stress tensor is to limit the model coefficient with a dynamic bounding of coefficients. A second way is to switch off the sub-grid scale model by using implicit LES. The results show that stress-realizability can ensure the numerical stability of the channel flow simulations even at high Reynolds numbers. Temporal and spatial correlations reveal that correlation functions are not the source for numerical instability. Nevertheless, it is found that strong gradients of mean and standard deviation of the model coefficient in time can cause numerical instability. The temporal imbalances occur faster and stronger in higher Reynolds numbers which represent the importance of stress-realizability in LES. Furthermore, the paper analyzes the performance of stress-realizable dynamic LES turbulence models in a variety of Reynolds numbers. A new scaling for turbulent viscosity variations with respect to Reynolds number is presented. Accordingly, the value of the PDF-realizability, in the form of a consistent sub-grid scale model for turbulent viscosity, in LES of wall bounded flow is illustrated. The results show stress-realizability is required to guarantee the numerical instability but is not sufficient in order to promise correct results. PDF-realizability becomes more vital when simulating complex flows including separation phenomenon in high Reynolds numbers.