The Influence Of Model Scale On The Starting Characteristics Of2D Hypersonic Inlets

As an important aerodynamic component of air breathing hypersonic vehicle, the starting characteristic of a hypersonic inlet plays an important role for the stability and efficiency of the scramjet engine. It has been reported that several famous flight tests were failed to achieve their test objectives because the inlet was unable to start as expected. Many factors such as geometry of inlet, flow conditions and the flight attitude etc., may affect the starting characteristic of hypersonic inlets. In this paper, a combined numerical and experimental investigation was carried out for the self-starting characteristics of a2-D hypersonic inlet, with a special focus on the comparison between different scale models. The work can be summarized as follows:1、The numerical results showed that the self-starting capability is reduced when the model scale is decreased, during which the corresponding self-starting Mach number may go up remarkably. It was also found that the inlet flow behaves similarly when the Reynolds numbers are close to each other even though the model scales are different in size, which demonstrates that the Reynolds number is a dominant factor characterizing the flow field.2、Furthermore, a kind of unexpected "self-starting" configuration was also observed experimentally under very low Reynolds number condition. With the CFD simulation, the laminar result is more similar to the experimental flow field than turbulence result.3、The numerical simulations demonstrated that for laminar flow, a separation zone spreads out nearly entire fore-body compression surface, which releases the high adverse pressure gradient and results in forming a supersonic path at the inlet throat. On the other hand, for turbulent flow however, the separation can hardly reach far upstream and consequently generates a strong concentrated separation bubble near the throat, which appears an obviously choked and unstarting configuration. It needs to be emphasized that although the laminar inlet flow behaves a starting-like characteristics, the captured flow ratio is evidently lower than that of the choked turbulent flow under the same incoming flow condition. Therefore the so-called "unusual self-starting" inlet flow observed in the present study is not a true self-starting flow in reality.