Numerical simulation of erosion in modified nozzles of axial flow turbine

Solid particle erosion in a turbine nozzle (turbine control stage) has been investigated by means of CFD. Literature attempt to couple fluid mechanics and erosion modeling and improvements in the hydrodynamics models together with improvements in the erosion models are reviewed. The solid particle bearing steam flow through the nozzle was investigated using a 3D numerical model and the finite volume code Fluent V6.0.12, looking for a reduction of the erosion process. The flow simulation was carried out for the original and modified (nozzle) designs with changes of the angle of particle impact on the nozzle surface. Numerical predictions have been carried out using the Renormalization Group (RNG) k-epsilon turbulence mode. To account for the influence of turbulent fluid fluctuations on particle motion, the stochastic tracking Discrete Random Walk model is used, which includes the effect of instantaneous turbulent velocity fluctuations on the particle trajectories. The removal of wall material due to erosion is calculated using the Finnie model developed for ductile materials. The numerical predictions showed a 50 percent reduction of the erosion rate for the modified (nozzle) design due to changes of the particles trajectories and impingement angle (angle of particle impact). The results obtained show that numerical simulation can be used in a predictive manner to solve a real practical design problem.