Force and Moment Measurements on a Free-Flying Capsule Model in a High-Enthalpy Shock Tunnel

Abstract

Experiments to measure the forces and moments acting on a blunted-cone capsule model are carried out in the High-Enthalpy Shock Tunnel, Göttingen (HEG). A free-flying arrangement is employed, whereby the model is initially suspended by weak threads that are detached by the arrival of the flow, allowing unrestrained flight during the steady test time. High-speed shadowgraphy is used to capture the model motion. Induced forces and moments are measured using both internally mounted accelerometers and visualization-based tracking techniques. Improvements to the visualization-based techniques allow the elimination of several previously identified sources of error. Measurements are performed over a range of angles of attack, and excellent agreement is obtained between the techniques. The precision of the visualization-based results is such that variation in the free-stream conditions is the dominant source of uncertainty in the drag coefficient, and is comparable to or larger than the standard error in the lift acceleration for angles of attack above approximately 6º. When applied to pitching measurements, all techniques suffer from large standard errors, but the visualization-based techniques show the capability to outperform accelerometer measurements.