RANS simulations of flow in a 3 D diffuser : ERCOFTAC Workshop test case 13 . 2
An incompressible fully-developed duct flow expanding into a diffuser whose upper and one side walls are appropriately deflected (two diffuser configurations differing with respect to the expansion angles were considered, Fig. 1), for which the experimentally obtained reference database was provided by Cherry et al. (2008, 2009), was studied computationally by using LES (Large Eddy Simulation), DES (Detached Eddy Simulation) and RANS-SMC (Reynolds-Averaged Navier-Stokes in conjunction with a high-Reynolds number Second-Moment Closure model) methods. In addition, a zonal Hybrid LES/RANS (HLR; RANS – Reynolds-Averaged Navier Stokes) method, proposed recently by Jakirlic et al. (2006, 2009) and Kniesner (2008), has been applied. The flow Reynolds number based on the height of the inlet channel is Reh=10000. The primary objective of the present investigation was the comparative assessment of the afore-mentioned computational models in this flow configuration characterized by a complex three-dimensional 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 the different modelling approaches to accurately capture the size and shape of the three-dimensional flow separation pattern and associated mean flow and turbulence features.