Scaling and flow dependencies over forward-facing steps

In the present paper, the structure of the mean separation bubbles upstream and downstream of a parametric forward-facing step (Ffs) is experimentally studied over a Reynolds numbers range of Reh=110,670−412,000, based on the step height and the free stream velocity. An array of 20 pressure sensors located on the front and on the top sides of the step were flush mounted for capturing the wall pressure fluctuations. Classical Piv was used to investigate the flow field topology and extract key features. The main interest of this study is to discuss the parameters affecting the reattachment length and the pressure statistics. A detailed analysis and comparison with the literature permitted to identify the most important flow quantities influencing the overall dynamics. Different sets of data with various Reynolds numbers, heights to boundary layer thicknesses h/δ, and constriction ratios CR, have been compared and considered exhaustively. The wall pressures space-time correlations and convection velocities of the large-scale structures downstream the step are highlighted. A focus on the spectral behavior of the unsteady pressure footprint inside the recirculation region on the top side of the forward facing step have also been investigated to deeply understand the unsteady processes described in the literature. Results demonstrate the existence of a convective instability process and a flapping phenomenon within the shear-layer that contributes to the separated flow arrangement.