Numerical simulations of the turbulent flow in an asymmetric two-dimensional diffuser are carried out using three commercial CFD codes: CFX, Fluent, and Star-CD. A low-Reynolds number $k$-ε model with damping functions and the four-equation $v′2¯−f$ model are used; the first one is available as a standard feature in all the codes, the $v′2¯−f$ model was implemented using the User Defined Routines. The flow features a large recirculating zone due to the adverse pressure gradient in the diffuser; the $v′2¯−f$ predictions agree very well with the experiments both for the mean velocity and the turbulent kinetic energy. The length of the separation bubble is also computed within 6 percent of the measured value. The $k$-ε calculations do not show any recirculation and the agreement with the measurements is very poor. The three codes employed show very similar characteristics in terms of convergence and accuracy; in particular, the results obtained using the $v′2¯−f$ are consistent in all the codes, while appreciable differences are obtained when the $k$-ε is employed.

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