B. W. Skews - Flow Research Unit, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, South Africa
B. Ndebele - CSIR, Department of Mining, Manufacturing, Defense, and Security. Meiring road, Brummeria, Pretoria, South Africa

Experiments and numerical simulations were conducted in order to examine the flow field surrounding a flat-faced body impacting on a flat surface. In the experiments impact velocities ranged up to nearly ۵ m/s. Visualisation was with a standard z-format schlieren system using a high-speed camera. The associated flow field exhibited ejected gas jets, shed vortices and weak compression waves in the external flow, as well as in the gap depending on pressure differences between the gap and the external field. A computational fluid dynamic simulation (CFD) was undertaken, enabling detailed evaluation of: the flow in the gap, the flow of the emerging jet near the impacting surface, and the development of the wave system and flow on the upper and lower surfaces of the impactor during its descent. It was found that very high pressures are generated in the gap between the impactor and impacting surface and that the jet emerging from the periphery of the impactor can reach supersonic velocities.

Compressible flow, Transient jets, Shed vortices