An exploration on the unusual self-starting behaviors of a hypersonic inlet under low Reynolds number condition

With the help of combined experimental observation and numerical analysis,an in-vestigation is carried out on the unusual self-starting behaviors of a 2-D hypersonic inlet under low Reynolds number condition.Based on a series of repeated shock tunnel experiments,it is found that with a continuous decrease of the unit Reynolds number,an unexpected inlet self-starting configuration reappears after the unstarting process.The observation of the flow field a-grees fairly well with the results of the laminar simulation,but differs remarkably from the com-putational results obtained with turbulent model.The numerical simulations demonstrate that for laminar flow,a separation zone spreads out extensively to nearly entire forebody compression surface,which releases the high adverse pressure gradient and results in forming a supersonic path at the inlet throat.However,for turbulent flow,the separation can hardly reach far up-stream and consequently generates a strong concentrated separation bubble near the throat, which appears as an obviously choked and unstarting configuration.It needs to be emphasized that although the laminar inlet flow behaves with starting-like characteristics,the captured flow ratio is evidently lower than that of the choked turbulent flow under the same incoming flow con-dition.Therefore the so-called “unusual self-starting”inlet flow observed in the present study is not a true self-starting flow in reality.