Investigation On The Starting Characteristics Of Hypersonic Inlet

The flowfield in hypersonic inlet was investigated by both experimental and numerical methods to study the starting characteristics and starting ability enhancement.Started and unstarted flowfields of 2D and 3D sidewall compression inlets were studied by wall static pressure measurement, schlieren, wall surface oil flow pattern and numerical simulation. It is achieved that the typical character of an unstarted flowfield is a large-scale flow separation near the entrance of internal compression, which causes much flow spillage. The separation keeps a balance among incoming flow, pressure rise caused by internal compression and spillage by adjusting its scale and position. And this balance forms a kind of self-sustainment of the separation which stabilizes the unstarted status. The influence of 2D inlet sidewall configuration on starting ability was also tested in this part.High speed schlieren was employed to observe the starting process of hypersonic inlets. Results show that the starting process can be divided into two parts: separation confrontment period and status transition process. The moment that separation-induced shock getting into the internal compression and spillage vanishing appears to be the critical condition of self-start.. The self-sustainment of separation is broken down when this moment occurred and then the inlet finishes the self-starting process.Based on the starting characteristics of one-dimensional, isentropic internal compression inlet, the starting characteristics of hypersonic inlet is achieved. The CR_in/Mach number diagram is divided into three distinct parts: spontaneous start region, dual solution region and cannot-start region.A 3D inlet with moving entrance door was tested in free-jet experiment and the result revealed that the moving entrance door could effectively improve the starting ability. The inlet avoids the starting hysteresis by blocking the entrance during acceleration. And the opening process after acceleration leads the inlet into dual solution region from spontaneous region which keeps the inlet started.Boundary-layer bleed was applied both on the forebody and in the separation region of unstarted flowfield. And this method is testified to be a simple but effective way to improve inlet starting ability. The results reveals that boundary-layer split on the forebody has the best effect, while the porous surface in the separation region has the highest bleed efficiency.The design method and starting characteristics of a streamline-traced Busemann inlet were investigated. The free-jet test result shows a very good performance at designed Mach number. But it cannot self-start at a lower Mach number unless with the help of bleed holes.