Four turbulence models: Realizable κ-ε

S-A(Spalart-Allmaras)

SST(Shear stress transport) and RSM(Reynolds stress equation model)

were compared by simulating separated flow in a diffusing S-duct.The numerical results show the capability of each turbulence model in dealing with separation.Before separation

the predicted results agree well with experiment for four models

but in separated region

the turbulence model has important effect in simulating separation.SST model is compared to RSM in simulating separation and pressure coefficient

however not as clearly as RSM.S-A model under predict the separation and the separated region is smaller than experiment.Mach number is higher than experimental data for four models.Pressure recoveries are similar for different models

and are within 0.7% agreement with experimental data.