Free-flight force and moment measurements with telecentric visualization technique in a Mach 6 reflected shock tunnel

Force and moment measurements of a test article in hypersonic flow are historically challenging. Among the techniques developed for such measurements, the free-flight optical-tracking technique has become increasingly popular due to its non-intrusive nature and recent developments in light-source and camera technologies. In this work, we replace the traditional visualization setup with a telecentric visualization system to track a free-flying sphere at Mach 6. This telecentric visualization system is calibrated first on a benchtop, showing significant improvements in edge-tracking accuracy, then applied to experiments conducted in a reflected shock tunnel. In addition, regularization methods were evaluated to replace traditional second-order differentiation for deriving accelerations from displacement data. Improvement in the accuracy of the tracked motion and drag coefficient of the test article was found when combining telecentric visualization with an edge-tracking algorithm and regularization methods.