Research On Variable Geometry Inlet Integrated With The Forebody Of Aircraft

As the connecting part between the forebody and the propulsion system,the inlet plays an important role in the integrated design process of them.In order to explore an integral design method of the rectangular variable geometry inlet and forebody,a rectangular variable geometry supersonic inlet with the design Mach number of 4.0 was studied by the numerical simulation.The effects of bleed at the throat station and the length of the aft diffuser with the cross section transforming from rectangle to circle on the flow field characteristics and aerodynamic performances of the inlet were analyzed.On this basis,the integrated design of the rectangular variable geometry inlet and the forebody of aircraft is carried out.The flow field characteristics and aerodynamic performance of the integrated inlets are obtained and analyzed.Firstly,in order to alleviate the shock wave/boundary layer interaction between the boundary layer and the background shock,and also to improve the stability margin of the terminal shock train,at the throat station,the effects of three different bleed positions and bleed ratios on the flow field structures and aerodynamic performances in the design state were studied and compared.The results show that:in the research scope of this paper,when bleeding on one side wall is used at the throat station,the throat Mach number is increased and the symmetry of the terminal shock train is destroyed,which has a negative impact to the performance of the inlet.When bleeding both on the two sides,the terminal shock is a single shock with good symmetry.The performance of the inlet increases first and then decreases with the change of discharge.The overall performance of the inlet is the best when the bleed ratio?=2.23%.Secondly,in order to study the influence of the length of the rectangle-to-circle diffuser on the performances of the supersonic variable geometry inlet,the effects of the different initial positions of the rectangle-to-circle diffuser on the flow structures and aerodynamic performance of the inlet is studied when the upstream geometry of the inlet is unchanged.It is found that the performance of the inlet increases first and then decreases with the initial position of rectangle-to-circle diffuser moving upstream.When the length of the rectangle-to-circle diffuser L₂=2.87H₁,the backpressure of the inlet is the largest and the total pressure recovery coefficient is the highest.Finally,based on the selected variable geometry inlet,the integrated design of the variable geometry inlet and the forebody with and without diverter is carried out on the basis of that the captured mass flow and the total bleed ratio of the inlet before and after integration are equal.The flow field structure and performances of the inlet were obtained by numerical simulation.It is found that,based on the integrated design of the forebody and the variable geometry inlet,the influence of different type forebodies to the inlet is fully considered.The forebody without diverter makes the use of the spanwise pressure gradient of the bump to effectively divert part of the forebody boundary layer.In the design of the variable geometry inlet with diverter,the inet can obtain a larger internal contraction ratio.However,due to the relatively thick boundary layer on the side wall,the overall performance of the inlet is slightly lower than that in the case of the forebody without diverter.