Interpretation of separation lines from surface tracers in a shock-induced turbulent flow

Abstract

IN experimental studies of shock wave turbulent boundarylayer interactions, surface-tracer methods, which have essentially zero frequency response, are widely used to determine the locations of separation lines. However, recent research has shown that in many cases the separation shockwave structure undergoes large-scale motion, raising questions about the physical meaning of separation lines deduced from such techniques. In the present study at Mach 5, the separation induced by an uriswept semi-infinite circular cylinder has been studied using platinum thin films. Conditional sampling analysis of the signals suggests that this line is the downstream boundary of a region of intermittent separation. Contents In experimental studies of shock wave turbulent boundarylayer interactions, surface tracer techniques are widely used to locate separation lines.1 Such methods are easy to use and generate sharply defined, repeatable separation lines (S). Quantitative measurements of flow length scales and angles are made using these methods and are used for evaluating the predictive capabilities of numerical methods and turbulence models. It is, therefore, important to understand what these lines physically represent. In many of these flows, dynamic wall-pressure measurements show that the separation shock is unsteady and moves from the upstream boundary of the flowfield, where the wall