Large-scale motions in a supersonic turbulent boundary layer on a curved surface

This paper presents measurements in a Mach 3 turbulent boundary layer which was subjected to a short region of concave surface curvature. Mean velocity and time-averaged turbulence measurements are presented to indicate the severity of the distortion, although the focus of this study is on how the large-scale organized motions are affected by the distortion. The primary tools in this investigation were multiple point hot-wire measurements and conditional sampling techniques. A 12° increase in the inclination angle of organized motions was observed and correlation measurements indicate an increase in the streamwise length scale. VITA conditional sampling was used to identify strong positive streamwise mass-flux gradients as the large-scale structures responsible for the measured structure angle. This technique was also used to determine that the convection velocity for the mass-flux gradients is approximately 0.9I7U_e in the undisturbed boundary layer and drops to 0.8U_e due to the distortion. VITA was also used to determine the ensemble-averaged flowfield associated with the mass-flux gradient structures. Again, the distortion caused significant changes in this flowfield, primarily in the outer half of the boundary layer.