| The supersonic jet exhausting in counterflow and crossflow is very complex problem owing to the nature of the jet interacting with the oncoming flow field and complex oscillatory shock structure. The supersonic jet exhausting in supersonic/hypersonic flows in counterflow direction has the oscillatory nature of the bow shock and is used for drag reduction of hypersonic vehicle. The sonic jet exhausting in the supersonic crossflow has the application in the attitude control for the fast moving vehicle in low density atmosphere whereas the jet exhausting in the quiescent flow has the application in thrust vector control, the estimation of unsteady side loads for off design conditions of rocket firing and flow mixing. The present study is aimed to apply the computational methodology for the shock induced separated turbulent flows and explore the mechanics in the jet interaction flow field. Specifically, the supersonic/sonic jet exhausting in the counterflow, crossflow and quiescent flow are investigated. The computational investigations are carried using a CFD code PAK-3D. The CFD code PAK-3D solve the Reynolds averaged Navier-Stokes (RANS) equations with a practical turbulence model to properly simulate the physics of supersonic and hypersonic two and three-dimensional jet interaction flowfield. The parametric study was performed to investigate the effect of pressure ratio, freestream Mach number and incidence. The mathematical models based on the calculations performed, were proposed defining the integrated effect in the form of force and moment. Further, the shock structures and flow physics for the three cases is discussed in detail.Firstly, a counterflow supersonic jet emanating from the nose of a hemispherical cylinder is investigated. Four different hypersonic oncoming freestream flows at various pressure ratios were solved using unsteady RANS equations with the two-equation k-εturbulence model. The investigations were mainly focused on two different flow regimes, SPM (short penetration mode)→LPM (long penetration mode) and LPM to ensure that the maximum drag reduction is achieved. For the present configuration being the hemispherical cylinder, the oscillatory flow regime SPM→LPM remains dominant over the most of the pressure ratios investigated. The obvious drag reduction is obtained for the higher Mach number flows at a constant pressure ratio, which can be attributed to the increase in relative mass flow rate of jet. The physical mechanism suggests that the drag reduction using a counterflow jet with different oncoming freestream flows can be expressed as a function of mass flow ratio. A model for the various freestream flows describing the drag reduction as a function of relative mass flow rate is proposed.Secondly, a sonic jet exhausting in the supersonic crossflow is investigated and series of numerical simulations were performed to evaluate the effectiveness of the jet with increase in pressure ratio and the angle of attack. The jet emanating from a blunted cone with a half-cone angle of 10.4°was used that provide possible directional control in supersonic flows. For an oncoming freestream flow of Mach number 4, the jet interaction in the crossflow causes an increase in net force and consequently a useful pitching moment is obtained through altering pressure distribution in its near forward and aft vicinity of the jet. A model describing the computed static aerodynamic coefficients variation with pressure ratios and angle of attack are presented to demonstrate this jet interaction effect. The shock structures, pressure and Mach number contours with streamline patterns gave a qualitative insight. For jet exhausting in the quiescent flow, the supersonic flow through various area ratio convergent-divergent, CD nozzles was investigated for both "designed "and "off designed" conditions. For CD nozzle operating at designed conditions, a reasonable agreement was found with the published experimental results. Further a jet vane was placed at supersonic exhaust of the CD nozzle. Two extreme test cases were studied with zero and 20°of jet vane deflection. For the off designed conditions, the nozzle area ratio Ae/At ranges from 1.2 to 1.6 with various nozzle pressure ratios NPR. At lower end of Ae/At and NPR, the shock structure inside the nozzle may be regarded as a normal shock. At lower Ae/At and moderate NPR, a well defined symmetricλ-shock was observed. For Ae/At = 1.3 with NPR≥1.70, a well defined asymmetricλ-shock structure was observed. The asymmetricλ-shock structure suggests that jet plume can be used for the mixing enhancement. |
