Evolution of turbulent boundary layer over a three-dimensional bump

A bump is typically used in the inlet system of an aircraft engine to compress the incoming airflow and to reduce boundary layer thickness developed over fuselage. In this work, the turbulent flow over a three-dimensional bump is experimentally studied. The bump model is mounted in a closed return wind tunnel operated at the nominal velocity 10 m/s, corresponding to a friction Reynolds number of 2300. The flow field upstream the bump, along the bump centerline and at two different spanwise planes is measured with Particle Image Velocimetry (PIV). It is observed that a favorable pressure gradient develops until the suction peak of the bump, and that the average turbulence intensity within boundary layer is attenuated due to this favorable pressure gradient. The boundary layer thickness identified by examining profiles of streamwise velocity decreases significantly along the bump. The wall-normal position of the Turbulent/Non-Turbulent Interface (TNTI) identified with the vorticity criterion is also observed to decrease along the bump. When studying the behavior of the boundary layer thickness at different spanwise positions, we found that it tends to be larger in planes away from the centreline, which suggests that the bump diverts the flow.