ABSTRAKT

Improved cooling of typical internally air-cooled gas turbine vanes and blades is proposed, with the intention of reducing temperature gradients within the blade material. Inside and/or outside blade surfaces are covered with the graphite foil, which has an anisotropic heat conductivity, as well as with the protective metal foil. It is supposed that the good contact heat transfer between the blade material and the graphite foil can be assured by vacuum. On the rotor blades, artificial roughening of internal surfaces can compensate the low strength of the graphite foil, but with external surfaces the problem is more complex. Numerical calculations of temperature distribution, performed for typical heat transfer conditions, show advantages of applying the graphite foil with anisotropic heat conductivity. Temperature gradients are substantially reduced by applying the graphite foil on the inside and/or outside surfaces of the turbine blade, compared to the turbine blade of the same geometry but without the graphite foil. When applied to cooling passages, the graphite foil can reduce local concentrations of the heat flux, and thus the cooling-air consumption can also be reduced. Although there are technological problems that have to be solved to enable a successful application of this new approach to the cooling of vanes and blades, its potential in reducing temperature gradients within the turbine blade material, simplifying the cooling channels geometry, and thus the reduction of the cooling air flow rate and the pressure drop, seems to be worth of investigation.