Velocity measurements in a pressure-driven three-dimensional compressible turbulent boundary layer

The flow characteristics of a three-dimensional, compressible, turbulent boundary layer have been investigated experimentally. The three-dimensional boundary layer was generated by inclining a cylindrical afterbody at 10° angle-of-attack to a Mach 2.45 freestream. The objective of the study was to determine the mechanisms that govern the growth and behavior of pressure-driven, three-dimensional, compressible, turbulent boundary layers. Laser Doppler velocimetry was used to determine both mean velocity components and turbulence statistics. The results show a significantly thicker boundary layer on the leeward side of the body than in the windward region. This circumferential variation in boundary layer thickness is caused by a circumferential flow, which provides a mass surplus in the low-pressure, leeward region and a mass deficit in the high-pressure, windward portion of the boundary layer. In addition, the pressure discontinuity at the angular junction and the axial pressure gradient also play a role in the boundary layer growth. Turbulent normal and shear stresses peak in the inner third of the boundary layer, with an initial peak forming at the interaction of the oblique shock/expansion fan with the boundary layer. The highly turbulent fluid on the windward side of the body is transported towards the leeward region by the circumferential flow in the boundary layer.