Numerical Investigation of the Effect of Ash Particle Deposition on the Flow Field Through Turbine Cascades

Abstract

Ash deposition on turbine blade surfaces is studied in this work using a particle deposition model. The model involves the three main processes: particle transport to the blade surface particle sticking at the surface and particle detachment from the surface. The model is used to investigate the effect of ash particle deposition on the flow field through turbine cascades. The surface velocity and the downstream total pressure coefficient are calculated for the clean and the fouled blade profiles and used in this investigation. The profile of the clean blade is chosen from the literature for which flow field measurements are available. The two dimensional compressible flow field is solved for the clean blade using the RNG k-ε turbulence model with the two layer zonal model for the near-wall region. The results are compared to the experimental data. The flow field is solved at the conditions expected in modern gas turbines. The deposition distribution on the blade surface is calculated during three periods of 12 operating hours each assuming inlet particle concentration as 100 ppmw. The fouled blade profile is predicted after each period. Then the flow field and deposition calculations are repeated to account for the time-dependent particle deposition. The flow field is calculated for the fouled blade after operating hours and investigated using the experimental data and the numerical calculations of the clean blade. The profile loss of the fouled blade is also predicted and compared to that of the clean blade.