For providing information for the restart control of hypersonic inlets, the current paper involves experimental investigations of the restart process for two generic two-dimensional hypersonic inlets with different internal area contraction ratios. The experiment is carried out at a free stream Mach number of 5.0. In order to simulate the restart process of the inlets, initially the inlets operate at an unstarted state due to the large throttling ratio, and then a decreasing throttling ratio (TR) is formed by the continuously downstream movement of the flow plug. According to the results, the inlet with smaller contraction ratio can restart with the retreat of the flow plug, while the inlet with larger contraction ratio (denoted inlet B) can not. For inlet B, the entrance separation bubble can not be swallowed into the duct even though the back pressure is entirely removed, causing additional spillage above the cowl and leading to remarkable entrance shock oscillation.
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