The Hypersonic Low Noise Wind Tunnel Technique And Relative Experimental Studies

The accuracy of the results of the wind tunnel experiments has becom one of the most important reasons for the slow development of the hypersonic aircrafts.Conventional hypersonic wind tunnels suffer from high levels of freestream fluctuations which are typically one to two orders of magnitude above flight levels.So the experiments especial those laminar-turbulent transition experiments conducted in the conventional hypersonic wind tunnels will be lack of reliability.The study of the low noise wind tunnel which can provide uniform quite flow has become a important research area in the future aerodynamics experiment technique development.Firstly,this dissertation did research on noiselevel reducing technique.The settling chamber used the flow stabilizing fit to provide uniform flow for the nozzle.The quiet nozzle was design by the short nozzle designing technique based on Béziercurve.For the ?300mm low noise wind tunnel,the suction device in the throat area suck away the boundary layer to make the boundary maintain laminar.So it can minimize the influence on the main flow.Then,the calibration experments had beed done on the low noise wind tunnel in this paper.The performance of the high pressure air source,the vacuum system and the heater system is getted through the experiments.It is the understruture for the next work.Then the square low noise wind tunnel is calibrated in three different conditiong while the mach numeber is 6.The experiments results show that the integral mach number will slightly ascend with the raise of the total pressure.Accordign to the mach number distribution,the flow field character under all of the three conditon rearch qualified criterion,some of the reach the advanced standard.The flow field will improved with the raise of the total pressure.The fluctuation of the freestream is measured using the high frequency pressure sensor.The integral fluctuation is about 5‰,and it will reduce to 3‰ when the flow stabilizing fit is installed in the settling chamber.all in all,the fluctuation of the freestream is of small degree,and the low noise wind tunnel has reach its design objective.NPLS is adopted in the flow structure visualization of the supersonic flow over a two-dimensional prisms in this dissertation.When appearance factor is small,the prisms are submerged by the boundary,the boundary layer keep laminar and it will not separate.With the increase of the appearance and the increase of the step height,the boundary layer will have a sudden increase and there will be a induced shock wave in the front of the step.When the appearance factor is 0.5 and the height of the step is 5mm,there will be a separation region in front of the step and the induced shock wave and large scale vortex will appearance in the boundary layer.With the increase of the appearance factor,the range of the recirculation region will increase and the flow reattach position will move to downstream.Comparing with supersonic turbulence when the appearance is the same,results show that the rettach region will obviously increase and the waves will be more clear.