Experimental Study On Aerodynamic Thermal Protection Of Hypersonic Plate And Elliptic Cone

Aerodynamic heating and thermal protection are the major obstacles to the development of hypersonic vehicles.In the future,the thermal load of hypersonic vehicle will exceed the limit of traditional thermal protection materials due to the new requirements of higher Mach number,longer endurance and reusability.Based on this consideration,on the one hand,this paper studied on the typical Backward Facing step structure,which widely existed on airfoil,forebody,optical window and jet exit,to explore the shape optimization scheme of vehicles to reduce the thermal load.On the other hand,this thesis put forward an active thermal protection scheme with the combination of film cooling and transpiration cooling for windward side of an elliptic cone conformation extracted from real aircraft shape.In details,that was using a 3D semi-cycle nozzle to generate the gas film to cover the windward side,combined with the transpiration cooling at the leading edges on both sides.In this way,the global thermal protection on the windward side is realized.The related flow mechanics was investigated by Nano-tracer-based Planar Laser Scattering technology,Temperature Sensitive Paint technique and schlieren system in a hypersonic quiet wind tunnel.Firstly,the paper specifically introduced the research progress of aerodynamic heating effect based on two main factors: leading edge bluntness and Backward Facing step profiles.Meanwhile,the development and application of active cooling technology and aircraft thermal protection system were reviewed.Subsequently,the surface heat flux distribution and flow structure were measured at different leading-edge bluntness and Backward Facing step profiles under hypersonic conditions.The results revealed the effects of leading-edge bluntness and Backward Facing step profiles on downstream flow transition and surface thermal environment.It was found that the blunted leading-edge can effectively delay the transition of the reattached boundary layer,resulting in a significant decrease in the heat flux intensity on the surface downstream of the step.When the diameter of the leading-edge was equal to the height of the step,the heat flux density reached the lowest.In addition,the heat flux density of downstream flow field can be effectively reduced by changing the square Backward Facing step into 30 degree slope profiles.Then,based on the elliptic cone standard model,the aerodynamic heating simulation,active thermal protection layout design and wind tunnel test were carried out.Temperature sensitive paint was used to test the surface temperature rise and heat flux distribution of the windward surface under different cooling conditions in a hypersonic quiet wind tunnel.The effects of jet pressure ratios,angles of attack and cooling mediums on the cooling effectiveness of gas film and transpiration were investigated.The flow field structure under corresponding conditions was observed by schlieren technique,and the flow mechanism of aerodynamic thermal protection was analyzed.The results showed that the increase of jet pressure ratio was beneficial to the expansion of gas film coverage area,and the surface temperature rise decreased.The temperature rise and heat flux amplitude on the windward surface increased with the promotion of the attack angle,and the flow reattachment line downstream of the step moved forward and the shape of the backflow zone changed constantly.When the angles of attack increased to more than 10°,the high and low temperature stripped structure caused by centrifugal instability appeared on the windward side.With the increase of angles of attack,the effect of gas film coverage is continuously improved by the influence of transverse flow,and the development direction of the mixing layer formed by gas film and incoming flow was closer to the wall,as a result,the high temperature zone gradually weakens,but the influence of high-low temperature stripped structure formed by centrifugal instability on the downstream flow field strengthened.The active cooling effect got the best at 10° angles of attack,and the heat flux on the windward side basically dropped below 0.The cooling effect of carbon dioxide was better than that of air under the same supply conditions.