PIV measurements in a turbulent wall jet over a backward-facing step in a three-dimensional, non-confined channel

• We studied the flow dynamics of a turbulent wall jet over a backward-facing step.
• PIV and stereo-PIV measurements were done along the central and cross-flow planes.
• RANS using a RSM turbulence model was calculated and compared to the PIV results.
• Reattachment length was found shorter than those from the BFS in the plane channel.
• High population of streamwise vortices were found near the side walls and corners.

A study of a turbulent wall jet over a backward-facing step is especially of interest because it shows a rich phenomenon flow and a mechanism to alter the flow characteristics downstream of the step. However, studies on this flow configuration are rare. In this paper, we considered this flow configuration in a non-confined channel as the specific engineering applications of electrical rotating machines and alternator that can be found in modern wind generators of the power production industry and automobile engines. The turbulent wall jet over a backward-facing step in a non-confined wind tunnel had the jet Reynolds number of 24,100 and the step Reynolds number of 11,900. Particle image velocity (PIV) and stereoscopic PIV measurements were performed along the central plane and several cross-stream planes. Numerical simulation of the test configuration was conducted by solving the three-dimensional Reynolds Averaged Navier–Stokes (RANS) equations with the second-order closure Reynolds stress model (RSM). The mean flow fields and second-order statistical moments from the RSM simulation were compared to results that were obtained through the PIV and stereo-PIV experiments. The mean reattachment length obtained from the current configuration was much shorter than those from the backward-facing step in the plane channel. The stereo-PIV measurements in the cross-stream planes revealed a high three-dimensionality of the flow, a high population of streamwise vortice in the upper region, near the side walls and the corners formed by the side walls and the bottom wall. The obtained results also confirmed the presence of the wall-jet formation on the bottom wall.