Reduction of Solid-Particle Erosion on the Control-Stage Nozzle of a Steam Turbine through Improved End-Wall Contouring

The iron oxide scales exfoliated from the inner wall of a boiler tube and a main steam pipe is known to cause solid-particle erosion on the control-stage nozzle. A combined experimental and numerical investigation was conducted to explore the optimization method of end-wall contouring for reducing the nozzle's erosion damage most effectively. The results indicate that increasing the end-wall contraction ratio and (or) decreasing the distance between the starting point of end-wall contouring and the trailing edge can significantly reduce the erosion-induced weight-loss of the nozzle, and can slightly improve the nozzle efficiency, irrespective of the variation in the particles size distribution and the aerodynamic parameters of a steam turbine. A main reason of erosion reduction is that the movement of loading towards the rear of the nozzle cascade caused by these contoured end walls has reduced the incident velocity of particles. In this study, the weight-loss of the nozzle was reduced by 40—50 per cent, and the nozzle efficiency was improved by 0.4—0.5 per cent by improving the end-wall contouring of the nozzle according to the methods mentioned above.