Modification of the k-epsilon turbulence model for swirling recirculating flow in a pipe expansion

A modified turbulence model, incorporating anisotropic effects into the standard k-epsilon model, is proposed for the numerical simulation of swirling recirculating flow in a pipe expansion. The new modification follows the concept that the correction to the standard k-epsilon model is made only in the flow regions where the anisotropic effects are appreciable. The performance of the present hybrid k-epsilon model for two swirling flows with moderate and high swirl levels is better than that of the standard k-epsilon model and the modified k-epsilon model proposed by Abujelala and Lilley and is also competitive with our previously developed hybrid k-epsilon model. Moreover, the present hybrid modification provides a relatively simpler form compared to our previously developed model; this also helps alleviate the numerical instability in the calculation procedure. Encouraging improvement in the prediction of the size of the central toroidal recirculation zone using I:he present hybrid modification is also exhibited.