Investigation Of Opposing Jet And Transpiration Thermal Protection With Hot Fuel Gas On Hypersonic Vehicles

Hypersonic vehicle is a hotspot in aerospace in 21 century,and it's application will accelerate the process of developing the outer space and exploring universe.Thermal protection system(TPS),as a key technique on restricting the speed of hypersonic vehicles,has great influence on the design and manufacture of hypersonic vehicles.The traditional passive and semi-passive TPS can't endure the high Mach,long-time and repetitive fligh condition in future with the limitlation of structure and material.Hence,an advanced and effective active TPS must be developed to face the challenge of future flight condition.Then,a flow control thermal protection method got more attention which can prevent vehicles from high and long-time aerodynamic heating.Opposing jet and its its combinations are belong to the flow control TPS.The principle of opposing jet in hypersonic flow can be described as follows.The coolant gas is injected from the stagnation of blunt body,then the bow shock is pushed away from the blunt surface with the interaction of introduced jet stream and incoming free-stream.Hence,the aerodynamic heating can be reduced.Besiders,a low-temperature recirculation region appears around the jet protrusion which promoting the cooling effect.In this paper,the thermal protection characteristics of opposing jet and its combinations in hypersonic flow are investigated.The flow modes of opposing jet in different total pressure ratio(PR)are analyzed and six different flow structures are obtained.At first,the hypersonic flow around a blunt body is obtained with the opposing jet can't inject when the jet pressure is smaller than the pressure behind the shock wave.Then the opposing jet injects in subsonic and supersonic speed and the Short Penetration Mode(SPM)is observed with the the PR increases.The SPM turn to unstable Long Penetration Mode(LPM)with the PR still increases.The jet experience expand-contract process or expand-contract-expandcontract precess,which leads to two kinds of LPM structures.Finally,the LPM turn to stable SPM with the PR is big enough.The last SPM structures have effective thermal protection performance.The opposing jet experiments in hypersonic flow is achieved and the low pressure SPM,LPM and high pressure SPM structures are obtained.The experiment results are compared with the numerical results,proving the veracity of simulation methods.A light and small gas supply device,which uses fuel gas generating with solid fuel as coolant gas,is introduced for opposing jet thermal protection in hypersonic vehicles.A numerical study on drag and heat flux reduction in hypersonic flow with opposing jet is conducted to investigate the cooling efficiency of fuel gas.Detailed results show that the cooling efficiency weakens with an increase in jet temperature and can be strengthened by enhancing jet pressure.An platelet transpiration TPS is introduced to ameliorate the local thermal protection capacity of opposing jet blunt body.A numerical study on heat flux reduction in hypersonic flow with the combinational opposing jet and platelet transpiration is conducted.The introduced transpiration can promote the cooling efficiency.Then the influence of angle of attack on the combinational TPS is investigated.The transpiration can strengthen the thermal protection performance in in the windward.The thermal state of the whole blunt body is computed.The thermal state of the blunt body in opposing jet is solved,with the room-temperatrue and hot fuel gas are employed respectively.Then the influence of transpiration on the blunt body is investigated.the transpiration flow can create a barrier between body and hot flow and also absorbs heat reducing the heat flux,so it can promote the cooling effect remarkablely.Finally,the influence of hot fuel gas on opposing jet TPS is discussed.The hot fuel gas has little effect on promoting thermal protection performance,but the hot fuel gas opposing jet and room-temperature transpiration can achieve better thermal protection and higher thermal protection efficiency with smaller mass flux of coolant single low-temperature opposing jet.In this paper,the hot fuel gas and platelet transpiration are introduced to the opposing jet TPS to promote the thermal protection efficiency and simplify the injection structures,which are beneficial for the application of opposing jet in real flight.