Comparison between loss coefficients of smooth, smooth-thickened, and rough-thickened axial turbine blades

Abstract

Experiments have been performed in a six-blade-cascade with smooth, smooth-thickened, and rough-thickened blades. After performing experiments with smooth blades, plastic sheet for smooth-thickened and 50-grade emery paper for rough thickened (both of same thickness) are pasted on suction, pressure surface separately and over both surfaces together to study the effects of roughness caused by erosion and deposition over the turbine blades. Static and total pressures at cascade inlet, static pressure over the suction and pressure surfaces of the blades forming middle channel, total and static pressures and outlet flow angle at 15 per cent of chord downstream are measured at midspan height. Difference in loss coefficients with smooth-thickened and rough-thickened represents the effect of roughness without thickening, similar to the roughness generated by erosion. The results of rough-thickened blade can be used to simulate the effect of roughness generated by deposition. For the same roughness level, roughness caused by deposition is more detrimental than that by erosion. It is also observed that the performance deterioration and non-uniformity of flow at cascade exit is more for rough-thickened blades.