Expansion fans and shock waves arise in supersonic flow in order to conform to imposed boundary conditions, for example specific driving or back pressures and facilitation of fluid flow around a body. Expansion fan/shock wave interactions occur in a number of practical applications, particularly where two bodies are in close proximity. Instances particular to the aerospace industry where such an interaction takes place include store carriage and release from aircraft, engine inlet design and formation flying. Consequently, a fundamental understanding of an expansion fan/shock wave interaction and the resultant flow field is of importance. Li and Ben-Dor (1996) performed an analytical study of a two-dimensional expansion fan/shock wave interaction, using the shock equations (derived from the conservation of mass, the conservation of momentum and the first and second laws of thermodynamics) to predict the flow field properties. A further numerical study was conducted by Yao et al. (2013) to determine the effect of the interaction on the downstream shock reflection, specifically the transition between regular and Mach reflection. An experimental investigation of an expansion fan/shock wave interaction is necessary to further understand the complex interaction and subsequent flow field as well as validating the previous studies.
The present research focuses on experimentally and numerically investigating an expansion fan/shock wave interaction at various Mach numbers. The expansion fan and the shock wave were each generated by separate low aspect ratio wedges. The wedges were mounted a fixed distance apart at various horizontal relative positions to simulate the interaction as one body moved past another (see Fig. 1). A colour schlieren system was used to experimentally visualize the expansion fan/shock wave interaction and resulting flow field. Numerical simulations provided insight into the three-dimensional nature of the flow field and the effects these phenomena had on the experimental visualization. The fundamental flow physics of an expansion fan/shock wave interaction and subsequent flow field will be discussed, with particular reference to external flow as would pertain to store release and formation flying.
References
Li H and Ben-Dor G (1996) Oblique-Shock/Expansion-Fan Interaction – Analytical Solution. AIAA J Vol. 34, No. 2:418 – 421
Yao Y, Li SG, Wu ZN (2013) Shock reflection in the presence of an upstream expansion wave and a downstream shock wave. JFM 735:61 – 90
