Boundary-Layer Visualization in a Shock Tube

Abstract

In the gas flow behind the shock wave in a shock tube a boundary layer is formed along the tube wall. Within this layer the gas velocity decreases from the free stream value u₂ to zero at the wall. A thermal boundary layer is superimposed to the velocity boundary layer, with the temperature decreasing from the free stream value T₂ to the wall temperature T_W (normally equal to the ambient room temperature). The assumption of constant static pressure in the flow behind the shock results in the existence of a density gradient normal to the wall, the gas density near the wall being higher than in the free stream. This boundary layer can be visualized with appropriate optical methods, e.g. with a schlieren system, provided that the density gradient is large enough for being resolved.