Abstract: The hybrid RANS/LES approach is employed to compute the exterior time-average flow field of a vehicle. The three-equation turbulence model is employed as the RANS part in current research. To overcome the numerical oscillation induced by the normal stress ( ) transport equation and the elliptic equation which is used to constructed relaxation function f22 in the model, the algebraic form of the normal stress ( ) equation and the new eddy-viscosity equation are derived, based on the Boussinesq approximation and non-dimensional analysis. Then, the new hybrid semi- /LES model which can be used to compute the vehicle exterior flow field is obtained. The control equations of the new model employed the same k and equations as those in the realizable /LES model in commercial software Fluent, with an algebraic equation for and new eddy-viscosity programmed by Fluent-UDF. The comparisons between the results obtained by semi- /LES model and other hybrid RANS/LES models, entire LES and wind tunnel experiment show that the new model is more accurate and efficient to simulate the flow separation around the body surface and the wake vortex.

Key words: Exterior flow field, Large eddy simulation, Turbulence model