关键词: 超声速混压式进气道;变几何;超额定;黏性效应;数值模拟

Abstract: Proper (or good) and different design methods are needed for supersonic inlet development in different phases. The first stage is certainly concerned about shock system design with inviscid theory, and inlet geometry as well. However, in the reality of viscous conditions, flow structure is extremely complex at over-speed regime. Therefore inlet design method on the basis of inviscid theory, is unclosed in design logic. Understanding viscous effect and its outcomes may be helpful to improve inviscid theory applicability for over-speed regime at the first stage of inlet design, or may provide some empirical guidances for viscous modification. For a variable-geometry mixed-compression inlet designed at Mach 2.5, this paper investigated the reforming mechanism of viscous flow structure at Mach 3(over-speed regime).Flow structures of some geometry designs are obtained and analyzed. It shows, compared with inviscid flow structure, initial viscous structures, such as boundary layer near walls and free shear layers from shocks intersection point, decrease the transport capability of internal path. The back-pressure resulted from throttling effect compels upstream shocks strengthened, forming separation region and shock interaction structure. New balance is established when spillage is enough and inflow equals local outflow everywhere in virtue of the reformed flow structures. Efforts of compensation for throat height and elimination of shear layer in core flow validate this mechanism understanding. At critical regime induced by back-pressure or throttling there exist a kind of ‘initial instability’ or ‘little buss’ phenomenon, which may be an inhesion resulted from the distinct swings of inflow free shear layers. Designed shock system can be obtained and ‘initial instability’ disappears when throat height compensation rate is over 35%. Increasing the second external compression angle makes the intersection point go away from the region of internal path. So the condition to develop a shear layer is eliminated. ‘Initial instability’ disappears at the same back-pressure, which means the inlet ability has been improved to endure higher back-pressure.

Key words: Supersonic mixed-compression inlet;Variable-geometry;Over-speed regime;Viscous effect;Numerical simulation