Numerical analysis of supersonic jets impinging into an obstacle

Abstract

The supersonic underexpanded jet flows impinging into obstacles are generally found to be extremely complex. They contain mixed subsonic and supersonic regions, regions of shear layer, possibly stagnation bubble, instances of major flow instabilities, elaborate interaction of shock waves and expansion waves, and various discontinuities consisting of barrel shock, jet boundary, Mach dise, contact surface, reflection shock, plate shock, and subtail shock, which all heavily depend on the various flow parameters such as nozzle reservoir conditions, jet exit conditions, nozzle-to-plate spacing, and plate inclination angle if the jet three-dimensional. The objective of this thesis is to gain an understanding of the flow structures developed by the impinging jet flow, sepecially the effects of various flow parameters mentioned earlier on the surface pressure and temperature, Both the cold and high-enthalpy (heated) jets anr cosidered, with equilbrium high temperrature effects for air by means of specific jeat ratio and speed of sound given by the explicit polynomial functions of thermodynamic variables by Tannehill & Mugge included in the latter, The jets considered are basically axisymmetric, but three-dimensional flows have been also investigated for the jets impinging into an inclened flat plate. Moreover the unsteady oscillation shock waves and jet structures have been considered for the jets impinging into a perpendicular plate and into a Hartmann-Spreger tube, and for the supersonic flow past a spike-tipped body. In the case of the self-sustained oscillation of shock waves in the supersonic spiketipped body flow and in the impinging jet flow into a perpendicular plate, the shock wave instability initiated by the resonace of acoustic waves travelling back and forth between the reflecting surfaces, can be strongly coupled with the fate of the stagnation bubble, which is again fed by the shear layer impinging into a normal surface at a position near the reattachmen...