Blade Boundary Layer Effect on Turbine Erosion and Deposition

Abstract

As an extension to the inviscid gas flow particle trajectory model presented in earlier papers, a complementary model has been developed to establish the effect of the blade boundary layer on the trajectories of particles and thus on the resulting erosion and/or deposition. The method consists essentially in tracing particles inside the boundary layer with initial conditions taken from the inviscid flow model. The flow data required for the particle trajectory calculations are obtained by using a compressible boundary layer flow computer program. This model has been applied to the first stage stator of a large electric utility gas turbine operating with coal gas. Results are compared with the predictions of the inviscid flow model. It is shown that the effect of the boundary layer on the trajectories of particles smaller than 6 μm is important. Since the hot gas cleaning system of a pressurized fluidized-bed gasifier system is projected to remove particles larger than 6 μm diameter effectively, it is concluded that an accurate assessment of turbine erosion and deposition requires inclusion of the boundary layer effect. Although these results emphasize the relative importance of the blade boundary layer, the absolute accuracy of the method remains to be demonstrated and is thought to be largely dependent on the basic data concerning the erosivity and sticking probability of particles.

Multistage Turbine Erosion

“…The erosion rates of the first two materials, also considered in our original paper (1) , were calculated from Eqs. (9) . One of these materials is ductile having a maximum erosion angle of 20 and the other is brittle with minimum erosion resistance at 90° .…”

Computer Predictions of Erosion Damage in Gas Turbines

“…Recently Breitman et al (10) used a finite element procedure for solving the radial equilibrium equation for a particle laden flow over the s o surface. Mengeturk et al (11) and Balam and Tabakoff (2) used an outer inviscid gas flow with a two dimensional boundary layer to calculate axial machinery performance in particle-laden flows. The effect of secondary flows in modifying particle trajectories was examined by Ulke and Rouleau (13) and El-Sayed et al (14).…”

Particle and Vapor Deposition in Coal-Fired Gas Turbines

“…Inertial impaction is an important erosion and fouling mechanism for the pressure surface of turbine blades. A detailed and exact model of inertial impaction can be formulated in which particle trajectories are computed from the knowledge of blade to blade potential flow field superimposed on the boundary layers [4,16]. Such a model is useful for the purpose of estimating erosion since it predicts the location, frequency, magnitude and angle of impact as a function of particle size and initial coordinates.…”

“…The readers may consult Refs. [3] and [4] for a review of past literature on Brownian, eddy, and inertial deposition of particles on turbine blades.…”