The aerodynamic loading of radial and mixed-flow turbines

In this paper we investigate the possibility of correlating the aerodynamic loading of radial and mixed-flow turbines in some systematic manner, as is widely done and recognized for axial stages. The loading is shown to be closely related to incidence, and an optimum incidence angle is often calculated from the rotor blade number using centrifugal compressor correlations.

It is found that there are many examples of high-efficiency stages which have far fewer blades than these correlations suggest. The relation between blade loading, flow coefficient and isentropic efficiency is investigated in the results of tests on some 40 different turbine stages, and a good correlation is found to exist, with a clearly defined region of best efficiency on a map of loading vs flow coefficients.

Various lift and drag coefficients are also defined and calculated for a number of tested turbines, but in general these parameters correlate the data less satisfactorily than the blade loading and flow coefficients. The lift-drag ratio is, however, a useful parameter for optimizing highly loaded stage designs.