Backward-Facing Step. Separation and Reattachment

The backward-facing step is a canonical separated-flow benchmark, where the flow separates at a fixed geometric edge and reattaches downstream. The reattachment length is the main numerical measure of overall modelling accuracy. This case reproduces the Driver & Seegmiller experiment at a step-height Reynolds number of 36,000 and Mach 0.128. It is run as steady compressible RANS with the SA and k-omega SST models, each with a freestream and a total-pressure inlet paired with a tuned static-pressure outflow. Skin-friction, pressure, velocity, and Reynolds-shear-stress profiles are renormalized to the upstream reference station and compared against CFL3D and experiment, and the reattachment length is extracted from the skin-friction sign change along the bottom wall.

Comparison of Flow360 predictions against reference data. Click an image to expand.

Skin-friction coefficient along the bottom wall

Pressure coefficient along the bottom wall

Axial velocity profiles (SA) at x/H = 1, 4, 6, 10

Axial velocity profiles (k-ω SSTm) at x/H = 1, 4, 6, 10

Reynolds shear-stress profiles (SA) at x/H = 1, 4, 6, 10

Reynolds shear-stress profiles (k-ω SSTm) at x/H = 1, 4, 6, 10