Numerical and Physical Aspects in LES and Hybrid LES/RANS of Turbulent Flow Separation in a 3-D Diffuser

Abstract 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° and 2.56° respectively), and for which reference experimental and DNS databases were provided by Cherry et al., 2008 , Cherry et al., 2009 , Ohlsson et al., 2009 , Ohlsson et al., 2010 , was studied computationally by using a zonal hybrid LES/RANS (HLR) method, proposed recently by Kniesner, 2008 , 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.