Simulation of Particle dynamics through a Kaplan Turbine

Authors

Adel Ghenaiet  - University of Science and Technology Houari Boumediene/Faculty of Mechanical Engineering and Process Engineering, Algeria

Abstract

Erosion problem is one of the major problems that restricts the lifetime of water turbines as being damaged by erosion processes till final breakdown of the rotor blades. Erosive wear is a complex phenomenon, function of particle size, hardness and concentration, the direction and the velocity of water flow, and the base material properties and particle interaction with walls. Indeed as the particle motion is governed by the local flow pattern which changes significantly, there is no possibility to predict particle impacts without the knowledge of local flow details. This paper presents a numerical study of the dynamic behavior of sand solid particles entrained within water through the components of a model of a Kaplan turbine. The flow field is solved separately from the solid phase, and the flow data are transferred to the particles trajectory computations based on an in-house validated code. This code is adapting the Lagrangian approach and has been used in many published paper and still undergoing improvements to suit several turbomachinery cases. Presently different external forces are considered added to the turbulence effects whereas the particle size, shape and rebound are described statistically. The number of particles and seeding positions are specified according to the concentration profile. At the interface between stationary and rotating components, particles are transferred integrally without any averaging. As particles trajectories and locations of impacts are predicted, an appropriate erosion model is used to estimate local erosion rates and the metal loss. The fully 3D trajectories and erosion patterns around the distributor vanes and the rotor blades are discussed thoroughly. The vane and blade shape with rounded tip led to the clearance flow and corner vortex, which resulted in a complicated fluid-particle interaction that affected the erosion distribution. The proposed results may serve to identify regions where a special surface treatment is necessary to increase the lifetime of the turbine components.