Influence of surface roughness on the shock transition in quasi-stationary and truly non-stationary flows

The effect of surface roughness on the shock transition over flat wedges in quasi-stationary flows and concave and convex wedges in truly nonstationary flows is investigated experimentally. Saw-toothed roughnesses are used for flat wedges. Sand paper provides the surface roughness for the curved wedges. The experiments are carried out on a 40 mm x 80 mm shock tube equipped with a double exposure holographic interferometer. The incident shock Mach number range is 1.04-4.0 for nitrogen or dry air. For the curved wedges, the shock transition angles are determined by means of a streak camera technique with curved slits. It is found that the shock transition angles decrease with increasing surface roughness. For a flat wedge of 0.8 mm surface roughness, the transition angle is 10 deg smaller than that for a smooth flat wedge for stronger shocks. The experimental results are explained by reffering to a shock polar.