Spatio-temporal statistics of a turbulent boundary layer under unsteady adverse pressure gradients : data from Time-Resolved Particle Image Velocimetry

An unsteady adverse pressure gradient turbulent boundary layer was created by rapidly deforming a 0.45 m long ceiling panel of a boundary layer wind tunnel to the shape of a convex bump. The spatial strength of pressure gradient and the rate of change of pressure gradient imposed were independently varied using an electropneumatic control mechanism for the ceiling panel. Time-Resolved Particle Image Velocimetry (TR-PIV) was used to capture the response of the boundary layer for a range of adverse pressure gradients. This talk will focus on the spatial and temporal evolution of single- and multi-point turbulent statistics obtained from phase-locked ensemble averages of the TR-PIV data for 3 rates of imposition of pressure gradients corresponding to non-dimensional times, t^* (defined as the ratio of convective time scale to imposed unsteady time scale), of 4.38, 1.53, and 0.61. The friction Reynolds number of the incoming flow, Re_τ, was 940 and the boundary layer thickness, δ, was 42 mm.