VMS and OES-Based Hybrid Simulations of Bluff Body Flows

Abstract

The present article focuses on the improvement of the two components of hybrid RANS/LES models. In the LES component, a Variational Multiscale (VMS) formulation [17] is introduced with the dynamic control of Germano et al, [11]. In the RANS component, an Organised Eddy Simulation (OES) model is used, [4,39]. The impact of these modifications on several critical flows past bluff bodies is analysed. These are the flow past cylinder at Re = 140, 000 entering the critical regime because of blockage ratio confinement, a flow past a cylinder at Re = 1, 000, 000, as well as the flow past a tandem cylinder at Re = 166, 000.Key words: hybrid turbulence models, RANS, VMS-LES, OES, DDES, bluff body flows.VMS-and OES-based hybrid simulations of bluff body flows and the existence of asymmetric forces on the cylinder surface (Bearman, 1965;Schewe, 1983). The passage to the critical and supercritical regime highly interests the aeronautics design and from a fundamental research point of view, the reasons of vortex shedding disappearance in a specific supercritical Reynolds number range. The numerical simulation of the drag crisis and of the supercritical regime remain important CFD challenges. The supercritical regime offers the possibility of the boundary layer treatment as fully turbulent, which is a simpler situation in respect for turbulence modelling issues than the transitional regime corresponding to the drag crisis. In this context, LES approaches and advanced URANS and hybrid RANS-LES methods can be adapted in order to capture the boundary layer nature and the transition location. LES methods need a quite high number of degrees of freedom (of order 100-500 Million for the single cylinder's problem, Rolfo-Revell et al, (2013) [34], Rodriguez et al, 2013 [18]), whereas hybrid methods are generally more economic as seen in the collected articles of the 4th Hybrid RANS-LES methods symposium (Girimaji et al, 2015 [1]). The objective of the present article is to offer reliable hybrid methods needing relatively economic grids.

Recent Developments of the Navier Stokes Multi Block (NSMB) CFD solver

“…An example of DDES around a supercritical wing using NSMB can be found in the AIAA paper by Grossi et al 79 , in the context of the European research program ATAAC, Advanced Turbulence simulations for aerodynamic application challenges, http://cfd.mace.manchester.ac.uk/twiki/bin/view/ATAAC/WebHome. A considerable improvement of the detached eddy simulation has been accomplished within NSMB by implementing the OES modelling in the URANS part of the DES and DDES in case of fixed and moving bodies including fluid-structure interaction 7,80 . The DDES-OES modelling has been coupled with the ALE -Arbitrary Lagrangian-Eulerian Method 81 accounting for mesh movement and deformation during the fluid-structure interaction process for moving/deforming configurations.…”