Wall cooling by gaseous injection for a high-performance combustion system

The literature is reviewed and the effects of certain aerothermodynamic and geometric parameters on film effectiveness and local heat transfer coefficient are assessed. A difference in form and performance is recognised between the slots commonly used in research work end these used in practice. The developing film is modelled as a transition region preceding a potential core and followed by an asymptotic main region. For practical slots, it is shown that a transition region always exists in the film regardless of the injection velocity ratio; also, that the range of interest consists of the potential core end transition regions alone. A boundary layer theory for effectiveness is developed by taking account of the potential core and the jet-like nature of the real film. The resulting blowing group is tested against eleven very different practical geometry slots and excellent correlation of data is achieved. A universal equation is obtained for practical geometries of this general class. [Continues.]