Velocity measurements in a 3D shock wave laminar boundary layer interaction. Part 1: Low speed 2D LDV measurements

Single component LDV (Laser Doppler Velocimetry) measurements were obtained in the separated 2D thin laminar boundary layer over an elliptic cylinder. The ellipse had an axis ratio of 4:1 and the incoming Reynolds numbers based on the minor axis were 675 and 1350. Velocity measurements were obtained within 0.05 mm from the surface both in attached and reverse flow regions. Painting the model with matt black paint and covering the tunnel walls proved to be effective means of improving signal quality. Measurements were successful both in back and forward scatter modes. The velocity profiles measured with Bragg cells indicate that the flow is separated at the ellipse mid-chord and that the separation bubble extends far downstream in the wake. The velocity profiles in the attached flow region compare well with the results of a boundary layer computation.