Large Eddy Simulations: Wall Functions with Forcing given by Backscatter from a Scale-Similarity Model

Developing accurate wall functions for LES is a great challenge. This is indeed also the case also for RANS. It can be argued that it should be easier to develop accurate wall functions for LES than for RANS. In a well-resolved LES using wall functions, the task of the wall function is to give an instantaneous wall shear stress; this does probably not need to be exactly correct. Compare with inlet fluctuating boundary conditions: there are many (infinite) ways to impose instantaneous fluctuations that will yield accurate mean flow and Reynolds stresses. The present work presents LES with wall functions. Forcing taken from back scatter from a scale-similarity model is used in the wall-adjacent cells. The object is to increase and enrich the resolved turbulence in the wall region. The new approach is applied for fully developed channel flow and 3D hill flow. For channel flow, it is indeed found that the results are improved using forcing. However, for 3D hill flow, it is found that the effect of forcing is negligible.