Numerical Investigation On Characteristics Of Combined Cooling Of Opposing Jet And Transpiration Cooling For Nose Cone In Supersonic Flow

Nose cone is a structure commonly seen in hypersonic flight vehicles.As the speed of the flight vehicles increases,the thermal environment that a nose cone faces will become more and more severe,so a reasonable and effective thermal protection is needed.Opposing jet and transpiration cooling are two methods often adopted for the thermal protection for blunt bodies,but both of them have some shortcomings.The combined cooling of opposing jet and transpiration cooling that combines the advantages of the two cooling methods and makes up each other’s disadvantages,can improve the thermal protection for the blunt bodies.In this paper,the nose cone in the high-temperature and supersonic mainstream is taken as the research objet and the cooling mechanism,effectiveness and characteristics of the combined cooling of opposing jet and transpiration cooling are investigated by numerical simulation.The main content is as follows:The mechanism and effectiveness of the single-phase combined cooling are investigated,and its advantages are introduced by comparing the cooling effect with opposing jet and transpiration cooing.In the process of the combined cooling,part of the coolant flows through the slot at the leading edge of the nose cone and forms the opposing jet.The other part of the coolant flows into the porous medium,conducts heat exchange with the solid matrix,and forms the transpiration cooling for the nose cone.The coolant entering the mainstream zone covers on the nose cone surface and forms a low-temperature film which acts as insulation.Comparing with the opposing jet,a thicker coolant film will be formed on the nose cone surface,which can reduce the temperature and velocity gradient inside the boundary layer.Besides,the combined cooling can provide a better cooling effect for the nose cone.Comparing with transpiration cooling,the combined cooling can better protect the leading edge of the nose cone and the temperature gradient on the nose cone surface is smaller,namely a less thermal stress on the nose cone surface.The combined cooling can well protect the nose cone from heat under different conditions of the main flow,and a better cooling effect will be gotten when increasing the total temperature or Mach number of the main flow.The impact of five factors,including the width of coolant slot,the injection rate and type of coolant,the porosity and material of porous medium,on the cooling effect of single-phase combined cooling are studied.As the width of the coolant slot,the mainstream will more easily flow into the slot and influence the coolant flow,so the thermal protection effect becomes worse.Increasing the injection rate of the coolant can help increase the distance between the bow shock wave and the stagnation point,which is beneficial for the improvement in the cooling effect at the leading edge of the nose cone.The coolant with a lower density can push the bow shock wave farther away from the stagnation point of the nose cone and form a thicker lowtemperature film on the surface.The coolant with a larger specific heat has a smaller temperature increase when absorbing the same heat,which can help better protect the nose cone.The decrease of the porosity will increase the specific area inside the porous medium and enhance the heat transfer between coolant and solid matrix,thereby improving the cooling effect at the leading edge of the nose cone.With the increase of the thermal conductivity of the solid matrix of the porous medium,the temperature distribution inside the porous medium becomes more uniform,and the overall thermal protection effect for the nose cone becomes better.Liquid water is adopted as coolant to further improve the effect of the combined cooling,and the thermal protection characteristics of combined cooling with phase change is studied.The huge heat absorption during the phase change of liquid water is beneficial for the cooling effect.The cooling efficiency also increases with the increase of the total temperature or Mach number of mainstream,but the cooling efficiency is above 94% under different conditions.When the attack angle of mainstream is small,the liquid water inside the porous medium almost has no phase change,and the combined cooling at this time has a good thermal protection effect.When the attack angle increases to 6° and above,there is an obvious phase change inside the porous medium on the windward side of the nose cone,the temperature on the leading edge of the nose cone increases rapidly,and the temperature gradient on the porous surface is large.The works in this paper can provide reference for the design and the optimization of the active thermal protection system for hypersonic flight vehicles.