Experimental Examination of Shock Wave Phenomena in Ducts with Abrupt Area Expansions*

This experimental study explores the shock wave and flow field evolution as the shock propagates far downstream from an abrupt area expansion. Close to the expanded region's entrance, intricate phenomena arise, including the formation of a substantial vortex near the expansion corner, which eventually evolves into a steady shear layer. As the shock wave progresses beyond the expansion, it initially undergoes regular reflection from the walls and subsequently transitions to Mach reflection. This results in a series of reflected shock waves propagating slower than the incident shock wave, inducing significant pressure fluctuations behind the shock wave. These fluctuations persist for an extended duration, increasing in number and reducing in strength as the shock wave front advances further downstream until eventually they reach a uniform strength. The reflection pattern behind the incident shock wave effectively divides the region into two distinct parts: a highly transient region characterized by strong shock waves and pressure fluctuations and a steady-state region. Notably, the study highlights the extended duration of the highly transient region and its growth as the shock wave front moves downstream, an aspect not extensively reported in previous research.