Measurements by Means of Optical Tracking in the High Enthalpy Shock Tunnel Göttingen, HEG

Abstract

Measurements of aerodynamic forces and moments in ground-based hypersonic shock tunnels are complicated by the brevity of the available test time of these facilities. A practical way to perform these measurements in a nonintrusive way, avoiding possible interference with support structures, is the free-flight technique paired with optical tracking: After detachment from an initial support, the test model moves freely with the flow. A sequence of images is acquired at high speed capturing the model movement. An algorithm is used to match the model contour in the images with the known model contour. From the resulting model displacement over time, aerodynamic forces and moments are calculated by assuming constant acceleration during a time window of steady flow conditions. The development and implementation of this technique at the High Enthalpy Shock Tunnel Göttingen, HEG of the German Aerospace Center is described and exemplified using an experiment with a free-flying capsule model.