Assessment of drag measurement techniques in a shock tunnel.

ABSTRACT

Three force measurement techniques in a shock tunnel, the free-flight, movable-support force balance, and stress-wave force balance techniques were employed, and each technique's characteristics were assessed. For each force measurement technique, the system setup, data processing method, measurement uncertainties, and applied range of the test model size-flow establishment time were described in detail and compared. For a comparison and discussion, the drag coefficients of a circular pointed cone model with a semi-angle of 18.4° at a nominal freestream Mach number of 6 were measured. As a result, three force measurement techniques yield similar drag coefficients. However, the measurement uncertainties were increased in the order of the free-flight, the stress-wave force balance, and the movable-support force balance techniques. The main causes of the measurement uncertainties were the corner detection uncertainties for the free-flight techniques, and the propagation of the internal or external vibrations for the movable-support and stress-wave force balance techniques. To estimate the appropriate range of the test model size and flow establishment time for each technique's application, the force measurement systems of the present work and the available literature were compared. As a result of comparative discussion, force measurement environments that can be advantageous for each technique are suggested.