Mass transpiration cooling analysis at hypersonic Mach numbers using CFD tools

Navier-Stokes equations coupled with species continuity equation which govern the transpiration cooling are solved numerically using CFD tools in the conditions prevailing over the earth's atmosphere and that of the planet Mars. In the mass transfer cooling technique a cold fluid is injected into the boundary layer through a porous media such that coolant issues forth as a continuous mass. The CFD code developed is based on the finite volume method [1,2]. It uses Roe's upwind method for computations of inviscid fluxes. The modified non-dimensional N-S equations in the conservative integral form can be written as: aU/aT + 1/A f(s) F(.)ndS=0 Where, (U) over bar = 1/A f f UdA is the average value of the column vector of conserved variables U= [p, pu, pv, pE, pm(l)](T) in the control volume and F is the flux vector, m(1) is the mass fraction of the species 1 and other variables have their usual meaning. Earlier numerical investigations were carried out to study transpiration cooling at M-infinity = 8.5 over the earth's atmosphere [3]. The modified code is further used compute the flow fields over a flat plate for Mach numbers 6 and 7 and for Reynolds numbers of I and 2 million under the conditions prevaling over the planet Mars for different blowing parameters. The variation of skin friction over the flat plate in the earths atmosphere in presence of transpiration cooling for various blowing parameters is shown in Fig. 1. The effect of mass injection on the wall temperature and on the temperature normal to the direction of the flat plate are shown in Figs. 2 and 3. The analysis using CFD tools shows that the transpiration cooling has significant effect on the flow field profiles which results in the reduction of the heat transfer and skin friction at the wall and increase in the boundary layer thickness. Helium and carbon dioxide are found to be relatively more efficient coolants in the atmospheres of earth and Mars respectively. Preliminary investigations accounting for real gas effects in computations show promising results. Experimental investigations which are being planned in ISWRC shok tunnel will become very useful for code validation.