Part II. Research on the Performance of a Type of Internally Air-cooled Turbine Blade

A comprehensive series of tests have been made on an experimental single-stage turbine to determine the cooling characteristics and the overall stage performance of a set of air-cooled turbine blades. These blades, which are described fully in Part I of this paper had, internally, a multiplicity of passages of small diameter along which cool air was passed through the whole length of the blade. Analysis of the, test data indicated that, when a quantity of cooling air amounting to 2 per cent, by weight, of the total gas-flow through the turbine is fed to the row of rotor blades, an increase in gas temperature of about 270 deg. C. (518 deg. F.) should be permissible above the maximum allowable value for a row of uncooled blades made from the same material.

The degree of cooling achieved throughout each blade was far from uniform and large thermal stresses must result. It appears, however, that the consequences of this are not highly detrimental to the performance of the present type of blading, it being demonstrated that the main effect of the induced thermal stress is apparently to transfer the major tensile stresses to the cooler (and hence stronger) regions of the blade.

The results obtained from the present investigations do not represent a limit to the potentialities of internal air-cooling, but form merely a first exploratory step. At the same time the practical feasibility of air cooling is made apparent, and advances up to the present are undoubtedly encouraging.