Wind Tunnel Testing Considerations in Expansion Fan/Shock Wave Interaction Studies

Abstract

In the research into expansion fan/shock wave interactions, wind tunnel testing is an essential tool allowing controlled freestream conditions and variation of parameters of interest. However, certain considerations must be accounted for in the wind tunnel model design, data collection, and interpretation of the results in order to ensure good quality results and accurate interpretation thereof. Model design involved sizing of the model such that the tunnel is able to start, design of an attachment mechanism to allow mounting into the tunnel, prediction of the aerodynamic loads encountered by the model both on tunnel startup and during operation, and ensuring that the material strength of the model and support structure was sufficient to prevent failure. Schlieren flow visualization is the appropriate tool for the study of compressible flows, and careful attention was paid during setup to reduce the schlieren angle and place the cut-off at the correct location to minimise the optical aberrations of coma and astigmatism. When studying the schlieren results, visualization of the three-dimensional shock waves as regions, rather than lines, and the shock wave emanating from the lower surface of the expansion generator were taken into account for accurate interpretation. Adhering to these considerations allowed the physics involved in an expansion fan/shock wave interaction to be investigated.