Numerical and physical aspects in LES and hybrid LES/RANS of turbulent flow separation in a 3-D diffuser

An incompressible fully-developed duct flow expanding into a diffuser, whose upper wall and one side wall are appropriately deflected (with the expansion angles of 11.3 degrees and 2.56 degrees respectively), and for which reference experimental and DNS databases were provided by Cherry et al. (2008, 2009) and Ohlsson et al. (2009, 2010), was studied computationally by using a zonal hybrid LES/RANS (HLR) method, proposed recently by Kniesner (2008) and Jakirlic et al. (2009). In addition a complementary Large-Eddy Simulation (LES) method has been applied. The flow Reynolds number based on the height of the inlet channel is Re(h) = 10,000. The primary objective of the present investigation was the comparative assessment of the computational models in this flow configuration characterized by a complex 3-D flow separation being the consequence of an adverse-pressure gradient evoked by the duct expansion. The focus of the investigation was on the capability of different modelling approaches to accurately capture the size and shape of the 3-D flow separation pattern and associated mean flow and turbulence features. (c) 2010 Elsevier Inc. All rights reserved.