Multi-resolution, time-resolved particle image velocimetry of a turbulent boundary layer approaching separation

The evolution and characteristics of turbulent boundary layers subjected to a positive pressure gradient are common in many flows of industrial relevance and appear, for instance, on the suction side of high-lift wing sections or turbomachinery blading. The pressure gradient is associated with a deceleration of the external flow which results in a thickening of the boundary layer and reduction of the wall friction. Under strong adverse pressure gradient conditions, the wall friction reduces to zero as the flow begins to separate. From a numerical perspective these flows are difficult to model with methods of engineering relevance, such as Reynolds averaged Navier-Stokes simulations (RANS) and motivate experiments such as the one presented here to provide relevant validation data.