高超音速进气道的附面层问题

STUDY ON BOUNDARY LAYER OF HYPERSONIC INLETS

关键词:  高超音速进气道  边界层  空气喷气发动机

Key words:  Hypersonic inlet  Boundary layer  Air breathing engine

摘要:

本文论述了高超音速进气道所面临的严重附层面问题,高超音速附面层的特点,高超音速附面层对进气道性能的影响,影响附面层转捩和厚度的诸因素.对如何控制和改善附面层及在设计高超音速进气道时如何考虑附面层因素,亦提出了一些初步看法.

Abstract:

Very thick forebody boundary layer exists in front of the hypersonic inlet. The temperature within the boundary layer is very high and the mass flux very low.Itis detrimental to the inlet flow field if the thick boundary layer is ingested intothe inlet, and the boundary layer suction is difficult.Because of the presence of the thick boundary layer, the shock wave is displaced outward.So the real geometric wedge angle should be equal to that of the theoretical compression angle minus the equivalent angle of displacement thickness of the boundary layer.In the range of Mach 6-8 the boundary layer loss is about 40-50 percentage of the total pressure loss in the inlet.The transition of boundary layer beneath the forebody will delay at hypersonic flight with large positve attack and in cooling the inlet walls, meanwhile, the boundary layer will be thiner.The thickness of the boundary layer also depends on configuration and the arrangement of wing strakes.The improper forebody design will lead the boundary layer thickness to be greater than the inlet higbt in the area near the symmetry plane.Maintaining the flight with positive attack, cooling the surfaces, selecting a proper configuration of forebody, ang locating wheeler vortex generators are all the effective ways to control the boundary layer,For the flight by the lower side of hypersonic region, boundary layer suction is also available.