Experimental Analysis of Anisotropic Porous Lattice Substrates on Pressure Gradient Induced Turbulent Separation Bubbles

We investigate the impact of anisotropic porous lattice substrates attached to a flat-plate on pressure gradient induced turbulent separation bubbles (TSB). The flow upstream of the substrate has a Reynolds number of approximately 760 based on the momentum thickness of the incoming turbulent boundary layer. The adverse pressure gradient is generated by suction, with the mean suction velocity at 45% of the free stream velocity. To examine the effects, we utilize four different substrates of High (~0.8), Medium (~0.5) and Low (~0.15) porosities. All designs have high porosities in the wall normal direction, while the porosities in the streamwise and spanwise directions are varied. These substrates span the width of the flat-plate and extend both upstream and downstream of the time-averaged separation bubble. We collect Stereoscopic Particle Image Velocimetry (SPIV) data to analyze and compare the flow characteristics in cases with and without the substrate. The SPIV measurements are taken at three different streamwise planes: the centerline plane, as well as two planes located 50 mm on either side of the centerline. Preliminary analysis of the time-averaged flow fields reveals the time-averaged flow separation is eliminated. In addition, we observe air flow jetting out from the substrate onto the surface. The SPIV results are compared with Direct Numerical Simulations (DNS) results. Overall, these findings provide valuable insights into the behavior of TSBs over anisotropic porous lattice substrates.