Turbulent flow over a backward-facing step with a porous insert

This paper presents an experimental investigation of the effects of a porous insert downstream of a turbulent flow over a backward-facing step. Three cases are studied, namely two porous insert configurations of a backward-facing step flow, and a reference unobstructed backward-facing step flow. In each of these test cases, the expansion ratio of the test channel is maintained at 1.25, and the Reynolds number based on the step height and the maximum velocity is fixed at 6230. Particle image velocimetry is used to obtain extensive velocity measurements of several streamwise-wall-normal planes covering the region upstream of the step, as well as the recirculation and redevelopment regions of each case study. The results indicate a substantial reduction of the reattachment length depending on the location of the porous insert. An evaluation of first and higher order moment turbulent statistics also shows that while the inserts lead to a retardation of streamwise mean flow, they result in significant increments in turbulence intensities and Reynolds stresses, modifications in the directions of the transport of turbulent kinetic energy, and variations in Reynolds stress anisotropy in the recirculation region. Furthermore, the recovery of the mean flow is observed to be impeded by the presence and location of the porous inserts. The results indicate that the placement of porous inserts in a backward-facing step flow may result in heat transfer improvements.