Determining aerodynamic coefficients from high speed video of a free-flying model in a shock tunnel

Abstract

This paper describes the application of the free flight technique to determine the aerodynamic coefficients of a model for the flow conditions produced in a shock tunnel. Sting-based force measurement techniques either lack the required temporal response or are restricted to large complex models. Additionally the free flight technique removes the flow interference produced by the sting that is present for these other techniques. Shock tunnel test flows present two major challenges to the practical implementation of the free flight technique. These are the millisecond-order duration of the test flows and the spatial and temporal nonuniformity of these flows. These challenges are overcome by the combination of an ultra-high speed digital video camera to record the trajectory, with spatial and temporal mapping of the test flow conditions. Use of a lightweight model ensures sufficient motion during the test time. The technique is demonstrated using the simple case of drag measurement on a spherical model, free flown in a Mach 10 shock tunnel condition.