Turbulent flow over a backward-facing step is one of the classical tests to validate turbulence models in CFD. In the present work, steady-state turbulent flow over a backward-facing step was simulated using FLOW-3D1 with the Renormalization-group (RNG) k-ε model to account for turbulent viscosity. The Reynolds number was computed using the step height h and the inlet free-stream velocity. The test case was run for two different Reynolds numbers: Reh=5100 and Reh=44,000.

The numerical predictions were compared with the experimental results with the same flow configuration. Streamwise velocity profiles at different locations in the flow direction were in good agreement both qualitatively and quantitatively with the experimental results.

One of the main objectives of this work is to study the sensitivity of the results to the turbulent mixing length parameter tlen in the RNG model. The steady-state velocity was used to compute the reattachment length behind the step for different values of tlen and compared with experimental data. A grid refinement study was performed to find the least mesh resolution needed to capture the essential flow physics of the problem.