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

Abstract

Experiments to measure the forces and moments acting on a blunted-cone capsule model are conducted in the High Enthalpy Shock Tunnel Göttingen. 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. Drag, lift, and pitchingmoment coefficients are derived over a range of angles of attack up to 6 deg, and excellent agreement is obtained between the techniques. Results are also compared with those from numerical simulations, with agreement found to lie within the experimental error for the drag and pitching coefficients but slightly outside for the lift coefficients. The precision of the visualization-based results is such that uncertainty in the freestream conditions is the dominant source of experimental error in the drag coefficient, and it becomes comparable to or larger than the standard error in the lift and pitching accelerations at the maximum angle of attack tested.