Skin friction measurements by laser interferometry in swept shock/boundary-layer interactions

Measurements have been made of wall shear stresses in swept interactions of planar shock waves generated by a sharp fin and the two-dimensional turbulent boundary layer on a flat plate. Test conditions were Mach number 3.03, Reynolds number Ree - 1.5 X 104, wall temperature near adiabatic, and fin angles of 10 and 16 deg. Measurements were made using the Laser Interferometer Skin Friction (LISF) meter, which optically detects the thickness of an oil film on the test surface. The results show that such measurements are practical in high-speed interacting flows with a repeatability of ± 12% or better. Further, with proper data handling, LISF measurements appear feasible at very high shear levels, which were previously considered unobtainable. Dramatic increases in wall shear were observed in both swept interactions tested. These data are compared with computational Navier-Stokes solutions by Horstman and Knight wherein k-e and algebraic turbulence models were used. Both computations predict the overall measured c/ levels at a = 10 deg but fail to predict some features of the Cf distributions properly.