Physics of supersonic mixing layers in two non-parallel streams

Abstract

Two-dimensional unsteady state Navier-Stokes equations, energy equation, mass diffusion equation and continuity equation are solved to study the mixing characteristics of confined shear layers formed by non-parallel supersonic streams. The streams are of. air and hydrogen, which come into contact after passing over a finite thickness base. An explicit Harten- Yee Non-MUSCL Modified-flux-type TVD (total variation diminishing) scheme is used to solve the system of equations, and a zero-equation algebraic turbulence model, proposed by Baldwin and Lomax, is used to calculate the eddy viscosity coefficient. The turbulent diffusion and heat flux are calculated by using turbulent viscosity and the most probable turbulent Prandtl and Lewis number (Pr, = 0.91, Lw, =1.0). The flow is treated as non-reacting to describe the purely fluid dynamic effects. The main objectives of this research are to observe characteristics phenomena of the mixing flow fields, mixing shear layers and mixing efficiency. The merging angle, pressure ratio and velocity ratio between the two streams are taken as variable parameter. The merging angles are varied by 0°, 5°, 10°, 15° and 20°. Both pressure ratio and velocity ratio are varied for the merging angles by 0.667, 1.00 and 1.50, individually. Investigation showed that, high momentum exchange occurs within shorter length at higher merging angle. At downstream, reflection of shocks also increases with the increase of merging angle. High momentum exchange increases mixing efficiency and reflection of shocks increases the pressure drop at higher merging angles. Therefore, higher merging angle is most efficient in terms of mixing but least efficient in the region of high drag. At higher pressure ratio (Phydroge/nPair), high number of shock reflection at downstream increases the waviness of shear layer but decreases spreading of shear layer. Variation of overall mixing efficiency among the merging angles decreases at higher pressure ratio. Velocity ratio (Vhydrogen / Vair) variation shows similar qualitative nature as the variation of pressure ratio.