The Study On Supersonic Flowfield Structure Near Bleed Slots And Holes Under Dual-Main-Flow

Boundary layer bleed,as the most traditional flow control means at present,is applied in many fields because it is easy to implement and the mechanism is simple.Bleed is widely used in compressor blades,low speed wind tunnel floor,transonic wind tunnel test section,supersonic static wind tunnel throat successfully.Current research finds that while the hypersonic inlet is unstart under over-rated mode because of high angle of attack,cowl bleeding can improve the inlet starting performance significantly.However,previous studies are poor about dual-mainflow bleed.The study of performance evaluation and influencing factors of dual-mainflow bleed is to be carried out.The flowfield structure near the dual-mainflow bleed holes and slots is studied systematically by means of numerical calculation.The flowfield structure near the bleed holes and slots is studied at different working conditions with different structures of the bleed holes and slots.First,the flowfield structures under different pressure ratios are analyzed and the dual-mainflow bleed is divided into two types: supersonic bleed and subsonic bleed.Supersonic bleed can be divided into choked type and non-choked type.The study finds that the critical factor that affects the bleed efficiency and flowfield structure is the static pressure ratio of the mainstream on both sides.Meantime the depth-to-width(diameter)ratio of the bleed slot(hole),Mach number and the thickness of the boundary layer can also make a difference.The influence of these parameters on the structure of the flowfield is coupled with each other,and the influence on the bleed efficiency is different under different bleed types.Furthermore,for different three-dimensional structure,the bleed efficiency and three-dimensional flow field structure are studied respectively.Four different bleed structures including transverse slot,longitudinal slot,single hole and array of holes are studied in turn.The study finds that due to the three-dimensional effect,the bleed efficiency of these four suction structures is better than that of the two-dimensional structure.Longitudinal slots have the largest sonic flow coefficient due to the large flow direction scale.The bleed holes have strong suction performance due to the bow-shaped expansion wave.The flowfield structure of the transverse slot is two-dimensionally distributed,and the bleed performance is also equivalent to that of the two-dimensional slot.The study analyzes the typical flow field structure under different bleed types in the circular hole.Next,the porous coupling effect are also studied when holes are arranged in different directions.Finally,an inward-turning hypersonic inlet is selected to verify the effect of cowl lip bleed on the unstart performance of the inlet under over-rated conditions.In an three-dimensional hypersonic inlet model,the bleed type and bleed efficiency of the slots are studied,and the reliability of the work is verified.Based on the larger structural weight of the actual cowl lip,cowl bleed slot with an air-collecting cavity is proposed,and its advantages in cowl bleed are verified through numerical calculations.