| The mean flowfield and time-dependent characteristics of a Mach 5 cylinder-induced transitional shock-wave/boundary-layer interaction have been studied experimentally. The interactions were generated with a right circular cylinder mounted on a flat plate. The Reynolds number based on distance from the leading edge of the plate to the cylinder leading edge ranged from 4.5 x 106 to 6.1 x 106, and the incoming boundary-layer was transitional. The objectives of the study were to: (i) provide a detailed description of the mean flow structure of the interaction, and (ii) characterize the unsteadiness of the interaction based on fluctuating pressure measurements. Mean wall-pressure measurements coupled with planar laser scattering and surface visualization showed that the transitional interaction exhibits characteristics that are essentially a "composite" of an upstream laminar interaction and a downstream turbulent interaction. In the upstream region there is a laminar separation bubble that is characterized by a weak separation shock, a pressure plateau, and low relative mass/heat flux. The separated boundary-layer reattaches downstream of this bubble, about 4 diameters upstream of the cylinder. This reattached flow is characterized by high relative mass/heat flux, an increase in pressure and a rapidly thickening boundary-layer. The flow then separates again in a manner very similar to a low Reynolds number turbulent interaction. Statistical analysis of the pressure histories suggest that the entire interaction stretches and contracts in concert. Power spectral densities of the pressure fluctuations showed unsteadiness throughout the interaction with energy content in one of two frequency bands: one with a sharp peak from 1-2 kHz and the other with a broader peak at 7-10 kHz. The lower frequency is attributed to the interaction motion, whereas the higher frequency is found underneath the reattached boundary-layer. Cross-correlations and coherence functions in the interaction suggest that the overall unsteadiness is caused by motion of the reattachment point. |
