An investigation into the heat transfer aspects of transpiration cooling

Hobson, G. V
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Although transpiration cooling has been demonstrated to keep the metal surface temperatures, in a gar turbine, below that at which oxidation occurs even though the hot gas temperatures are in excess of the metals melting temperature, few experimental studies have been conducted on the heat transfer aspects of transpiration cooling. Especially the effect blowing has on a turbulent boundary layer that has developed over a porous surface that is heated by the mainstream. Many studies have involved the blowing or suction oi the boundary layer through heated porous plates. Trans. an cooling was exper cntally investigated by making use of an existing wind tunnel which was modified so as to simulate the heat transfer phenomenon resulting from blowing coolant through a porous wall into a heated mainstream. The existing wind tunnel was designed and commissioned by Krieg (13) who considered the momentum transfer aspects of transpiration cooling. The solution of the momentum equation by Krieg forms the basis from which this investigation was developed, the original solution procedure being put forward by Cebeci and Smith (7). Krieg developed a generalised two-dimensional finite-differunce compute* program to solve the incompressible momentum equations describing a blown boundary layer. This program was further developed as part of this effort to solve the compressible momentum and neigy equations so as to account for the heat transfer in the blown boundary layer. The program is used to predict the experimental results obtained from the literature as well is those ottained during the nine experimental runs on the wind tunnel. Freestream flow velocities varied from 4,^5 m/s to 14,95 m/s with correspoi ;.ng temperatures of 44,95°C and 33,00eC respectively. The blowing fr tion F, was varied from 0,0059 to a maximum of , temperature of 40°C. The numerically calculated profiles and tho: » obi lined expurim ntally, as well as one set presented by another researcher, compared well. Finally, recommendations for future studies have been suggested.
A dissertation presented in fulfilment of the requirements for the Degree of Master of Science in Engineering DECEMBER 1982