The Influence of Blade Lean on Turbine Losses

Three linear cascades of highly loaded, low-aspect-ratio turbine blades have been tested in order to investigate the mechanisms by which blade lean (dihedral) influences loss generation. The blades in all three cascades have the same section but they are stacked perpendicular to the end wall in the first cascade, on a straight line inclined at 20 deg from perpendicular in the second, and on a circular arc inclined at 30 deg from perpendicular at each end in the third cascade. Lean has a marked effect upon blade loading, on the distribution of loss generation, and on the state of boundary layers on the blade suction surfaces and the endwalls, but its effect upon overall loss coefficient was found to be minimal. It was found, however, that compound lean reduced the downstream mixing losses, and reasons for this are proposed. Compound lean also has the beneficial effect of substantially reducing spanwise variations of mean exit flow angle. In a turbine this would be likely to reduce losses in the downstream blade row as well as making matching easier and improving off-design performance.