Streamwise development of boundary layer properties over a rough wall turbulent boundary layer with pressure gradients

Previous research has shown that there are variation in the equivalent sand ground roughness with pressure gradient (PG) with varying levels of amplification reported. These variations could genuine or due to a combination of limited scale separation in previous studies where the log and wake region are not clearly delineated. In this study, we present results from an experimental study where we examine the development of a high Reynolds number flow (inlet Re_τ = 16,000) under the influence of different pressure gradients. The pressure gradient is generated by an airfoil (1.25m long) mounted in the free stream with its angle of attack imposing different PG histories. Planner PIV measurements are taken throughout the developing flow while drag balance and Hotwire measurements are carried out in the most downstream location (where the flow has recovered to ZPG state). Initial analysis shows that at the most downstream location, the sand grain roughness marginally depends on the PG history. Further analysis of the PIV data will be carried out and the results on the variation of sand grain roughness as well as flow structure will be presented.