Analysis of Scale Adaptive Approaches Based on the Rotta Transport Equation

Abstract

A zonal formulation of the scale adaptive simulation (SAS) approach for wall bounded shear flows based on the Rotta’s transport equation for integral length scale is contrasted with the \(SST-SAS\) model of Menter and Egorov (Flow Turbul Combust 85(1):113–138, 2010) with local triggering (seamless formulation). It is known that the SAS approach does not trigger to a scale resolving mode in attached/mildly separated flows even if grid supports the transition Menter et al. (4th Symposium on Hybrid RANS-LES Methods, Beijing, China, September, 2011). This work addresses the question whether a zonal formulation of SAS (\(k-\varepsilon \) formulation along with different norm for second derivative of velocity) could improve the triggering process from URANS to LES-like mode in attached/mildly separated flows. In order to study the effects of different formulations, both models were applied to different flow configurations ranging from fully attached to strongly separated, including stationary streamwise-homogeneous turbulent channel flow, flow over an S809 airfoil and swirling flow through a sudden expansion. We find that, in both formulations, even when grid is sufficiently fine to resolve the integral scale motions, the simulation only transitions to scale-resolving mode when the base URANS flow is naturally unstable.