Investigation on wall shear stress measurement in supersonic flows with shock waves using shear-sensitive liquid crystal coating

Abstract

Wall shear stress (skin friction) is one of the fundamental surface quantities in aerodynamics but its measurement remains challenging. This paper studies the measurement of wall shear stress vector fields in supersonic flows with shock waves using the shear-sensitive liquid crystal coating (SSLCC) technique. A previously developed SSLCC technique was improved and used for the measurement of wall shear stresses in a supersonic jet flow. Experimental results show that the flow structures including shock waves in the supersonic jet flow were visualized by the SSLCC technique; furthermore, the shear stress vector field over a planar surface induced by the supersonic jet flow was measured by the SSLCC technique. The shock waves and the compression-expansion repetitions in the supersonic jet flow were captured, respectively, by analysing the shear direction field and the skin friction line pattern. This work demonstrates the capabilities of the SSLCC technique to visualize and measure wall shear stresses in supersonic flows with complex shock waves.