Transonic flow field measurements using a laser velocimeter

A two-component dual-scatter Bragg-cell type laser velocimeter operating in the backscatter collection mode was used to measure velocity distributions in two transonic flows. Ambient atmospheric particles acted as scattering sources in all experiments. First, the velocity field near the nose region of a hemisphere-cylinder was measured at Mach 1.1 by both the mean value and the mode value of the particle velocity distribution. The result based on the mode value gave closer agreement with the theoretical value. Particle lag was taken into account in the data reduction. In a second experiment, profiles of the transonic boundary layer on a two-dimensional bump were obtained both upstream and downstream of the shock wave and in the shock/boundary layer interaction zone. For a separated boundary layer, the superiority of the optical probe over the material probe is clearly demonstrated.