Research On Flowfield Structure In Supersonic Boundary Layer Bleed Holes And Slots

Boundary layer bleed,which is the most realistic,simple and reliable flow control means used in hypersonic inlet in present,is applicated in supersonic inlet to control the development of boundary layer,reduce the shock wave boundary layer disturbance and inhibit the boundary layer separation.Though boundary layer bleed is widely used in engineering,the current studies of the flowfield structure near the bleed holes and slots is not clear.The study on it is important for us to understand the internal mechanism of boundary layer bleed and the best bleed scheme.In this paper,the flowfield structure near the boundary layer bleed holes and slots was studied systematically by means of experiment and numerical calculation.In the numerical calculation,the flowfield structure near the boundary layer bleed holes and slots was studied at different working conditions with different shaple of the bleed holes and slots.In the experiment,a series of system test parts were designed and processed,which can change the bleed chamber pressure,change the size of bleed slots,measure the bleed mass flow,display the flow field structure.And then NPLS and schlieren flow display method were used to get the flow field structure in the bleed slot.And the bleed mass flow in the experiment was also measured by sonic nozzle.Firstly,the supersonic boundary layer bleed was divided into three types according to the airflow velocity in the bleed slot: subsonic type / critical sonic type / supersonic type.It is shown that the influence of flow field parameters on the structure of the flow field is coupled with each other,and the bleed mechanism of different bleed types is different.According to the shape of the separation zone in the bleed chamber,the shape of the separation zone in the bleed chamber was defined: open and closed.The state of the separation zone in the particular bleed slot depends on the depth and width of the bleed slot and the back pressure of the bleed chamber.Secondly,the local fine flow field near the bleed slot was obtained by NPLS,and the development process of the flow field in the bleed slot was analyzed with different bleed chambers pressure.The change rule of flow field structure with different flow field parematers was got by analyse the local flow field structure near the bleed slot,which was got by schlieren technology.In addition,the mass flow rate of the flow field under different working conditions was measured.Finally,the numerical method was verified by comparing the numerical calculation results with experiment results.Furthermore,the numerical calculation of three-dimensional bleed holes with different configurations was made,including three-dimensional transverse slot,longitudinal slot,triangular holes,circular holes and porous arrangement.The flow field structure characteristics of different bleed holes were analyzed and the bleed performance was analysed by comparing the sonic mass flow coefficient.The results show that the flow field structure components of different configurations are the same,the distributions of flow field structure are similar but has its own characteristics.In addition,the bleed performance also vary from each other.The bleed performance of triangle hole and longitudinal slot is much stronger than the transverse slot's bleed performance,and the triangle hole's bleed performance is stronger than longitudinal slot's bleed performance.The results show that the stronger the 3D effect of flowfield in bleed holes and slots,the stronger the bleed performance is.The research results not only have strong engineering practical value.At the same time,it has important guiding significance to the design of the bleed device in supersonic inlet.Finally,a series of bleed slots were arranged in a simplified configuration of supersonic inlet.The flow field structure near the bleed slot was studied with different shock incident positions,including throttling state and non-throttling state.In addition,the same work was conducted with a center clapboard put in the bleed chamber.The results show that the bleed capacity of the bleed slot is closely related to the location of the shock,the state of the bleed chamber outlet and the center clapboard in the bleed chamber.