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Dynamic large eddy simulation: Benefits of honoring realizability

 
: Ahmadi, G.; Kassem, H.; Peinke, J.; Heinz, S.

:
Volltext ()

11th International Symposium on Turbulence and Shear Flow Phenomena (TSFP11). Proceedings. Online resource : Southampton, UK, July 30 to August 2, 2019
Darmstadt: TU Darmstadt, 2019
http://www.tsfp-conference.org/proceedings/proceedings-of-tsfp-11-2019-southampton.html
6 S.
International Symposium on Turbulence and Shear Flow Phenomena (TSFP) <11, 2019, Southampton>
Englisch
Konferenzbeitrag, Elektronische Publikation
Fraunhofer IWES ()

Abstract
The use of stochastic analysis enables a theoretically well based, systematic derivation of a probability density function (PDF)-realizable dynamic LES model. However, this PDF-realizable model is not always stable due to the
rare appearances of non-realizable SGS stress values. The stability of dynamic simulations is a difficult challenge specially in complex wall-bounded flow with high Reynolds numbers. Based on the premise that the sub-grid scale
(SGS) model contributions is relatively small, many researchers suggested implicit LES (iLES) as a realizable alternative. On the other hand, it has been shown that ensuring the fully realizability of the SGS stress tensor (stressrealizability) solves the potential instability of the dynamic
LES. Nevertheless, this approach implies dynamic bounding of the SGS stress in the dynamic LES calculations. Thorough realizability and stability analyses of PDF- and stress-realizable dynamic LES model (LDMK) are performed for turbulent channel flow and separated hill flow simulations covering a range of Reynolds numbers from very low to high. In addition, stability of dynamic LES of neutral Atmospheric Boundary Layer (ABL) on a flat terrain is investigated with with a Reynolds number Re five orders of magnitude higher than in other simulations. Results show that the stability of ABL computations is ensured
by enforcing the newly developed dynamic realizability bounds. The suggested method of stabilization is applicable to other dynamic LES models. Unlike the fully realizable model, iLES is not capable of producing any turbulent
viscosity as required for a high Reynolds number flow or coarse grid applied. This limits the applicability of iLES to simple flows with low Reynolds number (it is not applicable to ABL flow simulations).

: http://publica.fraunhofer.de/dokumente/N-630217.html