On The Flow Characterisitcs Of Axisymmetric Hypersonic Inlets With Nose Bluntness

Leading edge bluntness is the primary method for thermal protection of hypersonic flight vehicles as well as an important issue for the design of hypersonic inlets. Effects of leading edge bluntness on the inlet flow characteristics need to be investigated com-prehensively to optimize the design and to improve the performances of hypersonic inlet and flight vehicles. In this paper, the effects of forebody bluntness were investigated on axisymmetric hypersonic inlets by CFD simulations and wind tunnel tests. The main results are listed as below:The research methods, including method of characteristics, CFD simulation, ex-perimental facilities and corresponding experimental methods were illustrated. The method of characteristics was applied to the fast design of inlet forebodies. The accu-racy of CFD simulation was validated with the calculations of three kinds of hypersonic flows:the aerodynamics of HB-2standard model, the shock boundary layer interaction problem of an axisymmetric configuration, and flowfield of an axisymmtric inlet. The CFD results were compared with the corresponding experimental data and good agree-ments were found between them, indicating well reliability of CFD simulation in the computation of hypersonic inlet flows.The programs for fast design of hypersonic inlet forebody with sharp leading edge were built based on the method of characteristics(MOC), including forebody types of multiple cone surfaces, isentropic compression surface, and curvecone surfaces. As the subsonic region around the blunt leading edge limits the application of MOC to forebody design, a fast design method coupling forebody bluntness was developed by combining CFD simulation with MOC. Both the accuracy of CFD in the nose region computa-tion and the efficiency of MOC in inlet design were incorporated in the coupled design method. Under these bases, four axisymmetric hypersonic inlets were designed with the restriction of inlet exit Mach number. The forebody types of the designed inlets are bi-cone, tri-cone, initial cone followed with isentropic compression surface(hereafter shorten as isentropic configuration) and curvecone.The variations of flow characteristics of axisymmetic inlets with freestream Mach number and angle of attack were investigated on the previous four inlet configurations by CFD simulation. The sensitivities of forebody compression patterns to the variation of freestream parameters were also evaluated by comparing results of the designed con-figurations. For an axisymmetric inlet under freestream of angle of attack, the strength of airflow compression increase on the windward side while decrease on the leeward side. The differences of compression strength between windward and leeward side pro- duce aerodynamic lift, while degrade flow characteristics of inlet. For various inlet configurations, the compression patterns of inlet forebody affect the flow variations with freestream parameters. For isentropic and curvecone configurations, the compres-sion waves generated from curved forebody surfaces could adjust the shapes of leading edge shocks under the freestream with angle of attack or low Mach number, resulting in higher flowrate coefficient than that of bicone or tricone configurations. The isentropic configuration exihibits the highest total pressure coefficient than other configurations, and it was chosen for further researches as it has the best comprehensive performances.The effects of blunt nose scale on the flow characteristics of axisymmetric inlet were evaluated with CFD simulations and wind tunnel tests. The isentropic configura-tion was investigated with CFD simulations under various freesteam Mach numbers and angle of attacks. Corresponding experimental researches were carried out in a conven-tional wind tunnel at the freestream of Mach number6. It is shown that the variations of the inlet flowfield, inlet performances and experimental pressure distributions are negligible within5%cowl radius nose scales for the horizontal freestream. Obvious discrepancies of nose effects have been found between windward and leeward side of the axisymmetric inlet under the freestream with angle of attack. Variations of windward flowfield. inlet performances and experimental pressure distributions can be hardly no-ticed for current researches, while slip lines of leeward side move outward and leeward flowfields turn to be unstable with increasing nose scale. According to the experimental results of natural transition tests of3.2mm nose, evident separation appears on the lee-ward side of inlet at angle of attack of4°. The separation becomes more severe when the angle of attack increases and the leeward side of the inlet turns to be unstart at angle of attack of7°, which result in remarkable pressure drop. Forced transition tests were also carried out with trips. The tripped results of3.2mm nose at angle of attack of4°show prominent restrain of separation region and the separation shock turn to be invisible. Trips can also diminish the leeward separation region at angle of attack of7°, however the leeward side of inlet is still unstart.The effects of trips and nose scale on the buzz flows of axisymmetric inlet were conducted in a shock tunnel under the horizontal freestream. Trips show prominent suppression of oscillatory range of buzz flow. Due to the suppression of external sep-arations, the oscillatory frequencies of tripped cases are higher than that of untripped cases. Pressure magnitudes of tripped case are also higher than that of untripped case, owing to the enhancement of strength of separation shocks. The influences of nose scale on inlet buzz flow are minor than that of trips. The discrepancies of buzz flow between0.8mm nose case and3.2mm nose case turn to be remarkable with thinner trips, includ-ing the forebody flow structures, buzz frequency and surface pressure. For0.8mm nose cases,the thinner trips results are similar to that of previous tripped results. However, the thinner trips case of3.2mm nose is closer to that of corresponding untripped case.