A numerical calculation was performed to study the features of turbulent recirculting flow in a rearward facing step flow. As a closure model for the turbulent equations, the standard 2-equation model and the low-Reynolds number model suggested by Lam-Brenhorst were used. Although the standard high Reynolds number form of k-ε model has proven to be a powerful tool for the prediction of a wide variety of turbulent flows, it has to be combined with the "wall function" to bridge the viscous and buffer layers in proximity to the solid walls. This wall function approach can occur much inaccuracies for recirculating flows because it is strictly valid only for the attached shear layers. To overcome the problems connected with the introductions of wall functions, the low-Reynolds model was used in this calculation.
And also another numerical calculation was made to test in channel flow k-ε-γ model suggested by Cho and Chung 1991. Two other models, two-layer k-ε model and Lam-Bremhorst's low-Reynolds number model, were used to compare the results.
Computations for a rearward facing step flow show considerably good results or similar trends comparing with measurements, but a low-Reynolds number model predicts a shortend reattachment in the same way as the standard two-equation model. And the results using k-ε-γ model in a channel flow are in good agreement with the data calculated from the two-layer k-ε model and the low-Reynolds number model.
