Research On Complicated Flow Field And Heat Transfer Characteristic Of Forward-facing Cavity Combined With Opposing Jet Fortified Thermal Protection Configuration

Thermal protection system (TPS) is a key technique of the high speed vehicles’design and manufacture, it is connected with the safety of the aerocraft directly. Thedesign of TPS is always a challenging work for the high requirement from the aerocraftby its inclement and complex aviation environment.The present dissertation is about research of thermal protection system design forhigh speed vehicles. The numerical simulation mode of the flow field of surpersonic andhypersonic vehicle nose-tip is established, and this numerical method is validated byflow imaging experiment and experimental date in the open literature. Based on thenumerical simulation of the single opposing jet and single forward-facing cavity coolingmethod, a kind of the forward-facing cavity and opposing jet combined TPS is designedand investigated numerically.The influence of the opposing jet TPS on the flow field, aerodynamic force, andsurface aerodynamic heating of the vehicle nose-tip was investigated numerically. Theproperties of attack angle for opposing jet TPS was discussed, the useful attach anglerange of opposing jet TPS was obtained. When the attack angle reaches10, the heatflux on the windward generatrix is close to the maximal heat flux on the wall surface ofthe nose-tip without thermal protection system, thus the thermal protection is failure.A numerical study on the effect of forward-facing cavity upon aerodynamicheating on the hypersonic vehicle nose was conducted. The flow field parameters, heatflux distribution along the outer body surface and the cavity wall were obtained, thecooling effect of the forward-facing cavity with different dimension was analyzed. Theresults show that the forward-facing cavity configuration dose well in cooling the noseof hypersonic vehicles especially at the stagnation point area. The deeper the cavity is,the smaller the heat flux is. The maximal heat flux dose not locates at the peak of thesharp lip, the maximal heat flux of the outer body surface and upper wall of the cavityare all behind the lip peak. The cavity length has little effect on the location of themaximal heat flux. In sum, there is a low heat flux on the upper wall, but the maximalaerodynamic heating point is located on it. There is a very low surface heat flux alongthe base wall of the cavity except the cavity is shallow enough.The forward-facing cavity and opposing jet combined TPS was investigatedprimarily. The flow field parameters, aerodynamic force and surface heat fluxdistribution of this combined TPS nose-tip were obtained by numerical method. Theinfluence of the opposing jet stagnation pressure, Mach number and cavity length,diameter on the thermal protection efficiency of the TPS was discussed respectively.The performance parameter of the combined TPS with different opposing jet workcondition and cavity geometry parameter were obtained. This kind of combined TPS has an excellent impact on cooling the nose-tip of high speed vehicles. The recirculationregion plays an pivotal role for the reduction of heat flux. Under the same opposing jetstagnation pressure condition, with the opposing jet speed increasing, the coolingefficiency of the combined TPS is improved and the aerodynamic resistance isdecreasing. Under the same jet Mach number condition, with the stagnation pressure ofopposing jet decreases, the aerodynamic resistance is increasing but the heat flux alongouter body surface of the nose-tip does not increase monotonically. Under the sameflow condition (include the free stream and opposing jet flow), with a constant cavitydiameter, the combined TPS with larger length cavity has the higher heat flux reduction.The cavity length has little influence on the aerodynamic force. Both of theaerodynamic heating and the force do not variate monotonically with the cavitydiameter. There is an optimal choice of the cavity diameter for the aerodynamic heatingreducing of the nose-tip, in this researching, the aerodynamic heating has the minimumdistribution when the cavity diameter is6mm.The high-definition Nanoparticle-based Planar Laser Scattering (NPLS) is used toobserve the flowfield of nose-tip with the three different thermal protectionconfiguration, forward-facing cavity, opposing jet and their combined configuration.The complex structure of the flowfield with different thermal protection method can beobserved in detail, including the bowl shock wave in front of the nose and therecompression shock wave when the thermal protection method contains the opposingjet, and the bowl shock wave oscillation when the thermal protection method containsforward-facing cavity only. At last, these experiment images are compared with thecalculation results, there is a good agreement, which validates the calculation methodagain.