Assessment of erosive wear performance of Pelton turbine injectors using CFD-DEM simulations

Abstract

The problem of surface erosion due to sediment-laden water in hydropower stations is quite severe, especially in those located in the Himalayan region. It is one of the major causes of reduction in the operational economy for hydropower generation. In Pelton turbines, the injector assembly is subjected to severe erosion, yielding it inoperable in a relatively short period when compared to other parts of the hydropower plant. The present study aims to contribute to an understanding of hydro-abrasive erosion in Pelton turbine injectors due to changes in design and surface material with hard coating. Three different injector designs, conventional design (nozzle and spear angle of 90 o and 50 o , respectively) and two other designs proposed for better hydraulic performance (nozzle and spear angles of 110 o and 70 o , and 150 o and 90 o , respectively) are chosen for the analysis. The simulations are conducted using the CFD coupled discrete element method (DEM). Multi-size sand particles in the range of 75 μm to 300 μm have been selected to conduct the study. The particle-wall collision characteristics are used to estimate the erosion rate using the semi-empirical erosion models calibrated for martensitic steel, high-velocity air fuel (HVAF), and high-velocity oxy-fuel (HVOF) processed WC-CoCr coatings erosion. The erosion distribution on the nozzle and spear for different injector designs with and without coating at different nozzle opening conditions has been studied. The results show that the erosion of the nozzle and spear is asymmetrical. The increase in design angle enhances nozzle erosion while decreasing spear erosion. The erosion resistance of the Pelton injector improves by an order of 100 with a coating of WC–CoCr. Compared to the HVOF technique, coating with the HVAF technique has superior erosive wear performance. The ratio of maximum to minimum erosion ratio reduces with coating. Also, the uniformity in erosion distribution improves for the coated surface compared to the uncoated surface. The results could provide some theoretical assistance for design optimization, coating performance, and maintenance of the Pelton turbine injector for application in sediment-laden water flows. • Comparison of injector designs for hydraulic and erosive wear performance. • Comparison of the erosion of injectors with and without surface coating. • Erosion model for martensitic steel, and HVAF and HVOF processed WC-CoCr coatings. • Identification of zone of higher erosion on nozzle and spear for different designs. • Analysis of particle collision characteristics on nozzle and spear surface.