An Analysis of the Turbine Endwall Boundary Layer and Aerodynamic Losses

A momentum-integral analysis of the three-dimensional flow on the turbine endwall is presented. The formulation is for a compressible turbulent boundary layer with a constant streamwise shape factor. The effect of compressibility enters through a coordinate transformation and an assumed energy equation. An aerodynamic loss model is derived using inner and outer expansions. The losses decompose into frictional losses on the annulus and a vortex loss. Results are predicted for four cascade tests. In addition, previously observed trends of loss versus inlet boundary layer thickness, blade height, and blade chord are predicted. To illustrate a possible application, a parametric study is presented showing the effect on losses and heat transfer of various inlet boundary layer thickness distributions, which simulates different secondary flow configurations.