Numerical Investigation of Ash Deposition on Nozzle Guide Vane Endwalls

Abstract

A computational study was performed to determine the factors that affect ash deposition rates on the endwalls in a nozzle guide vane passage. Deposition tests were simulated in flow around a flat plate with a cylindrical leading edge, as well as through a modern, highperformance turbine vane passage. The flow solution was first obtained independent of the presence of particulates, and individual ash particles were subsequently tracked using a Lagrangian tracking model. Two turbulence models were applied, and their differences were discussed. The critical viscosity model was used to determine particle deposition. Features that contribute to endwall deposition, such as secondary flows, turbulent dispersion, or ballistic trajectories, were discussed, and deposition was quantified. Particle sizes were varied to reflect Stokes numbers ranging from 0.01 to 1.0 to determine the effect on endwall deposition. Results showed that endwall deposition rates can be as high as deposition on the leading edge for particles with a Stokes number less than 0.1, but endwall deposition rates for a Stokes number of 1.0 were less than 25% of the deposition rates on the leading edge or pressure surface of the turbine vane. Deposition rates on endwalls were largest near the leading edge stagnation region on both the cylinder and vane geometries, with significant deposition rates downstream showing a strong correlation to the secondary flows.