Prediction of thermal protection of walls by blowing with different fluids

This work concerns the modelling of heat and mass transfer in the boundary layer and inside a plane porous plate which is below a hot fluid flow and submitted to cold fluid blowing. A preliminary study of the heat transfer rates in the boundary layer without blowing permits us to validate, comparing with experimental results, the RNG k - epsilon model. The RNG k - epsilon model, with kinematic and thermal laws for the wall, linked with a model of blowing, is then used to study the heat and mass transfer rates at the wall when the main flow and the injected fluids are of the same species - air - but at different temperatures. The comparison between calculated friction factors, Stanton numbers and published results confirms the validity of our model. We also show the strong influence of the injection rate on the thermal convective coefficient of the wall. In the last part, results on cooling by blowing with water vapour in a main flow of air are given. Comparisons of the evolution of Stanton numbers and friction factors show that blowing with water vapour is more efficient than air injection in terms, of momentum transfer and thermal protection of walls. (C) Elsevier, Paris.