Present day turbine cascades are being optimized, usually, for minimum total pressure losses. Gas Turbines, however, operating in a dirty environment or using dirty fuels need cascades that minimize the erosion and the corrosion implications of the hostile environment of the flue gasses. The present study employs the parametric cascade optimization method by Mcdonald to study the influence of a number of parameters on the deposition velocity of various particles, typical of those in a PFBC Gas Turbine. The calculation code employs the TSONIC and the STAN5 codes plus the method of Stewart for the aerodynamic losses and two property chosen models for the eddy diffusion one. The results indicate that control is possible only for particles with a diameter of less than 10.0 μm and this usually at the expense of an increase in the aerodynamic losses.

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Gas turbine efficiency deterioration due to particulate deposition is a well known phenomenon especially in industrial machines which operate on “heavy” fuels. The result is the need for frequent blade surface cleaning after certain hours of operation. The present study investigates the flowfield modification and the corresponding aerodynamic losses due to the progressive particle deposition on the aerofoil surfaces of a representative turbine stator cascade. The flowfield is calculated with the Katsanis (TSONIC) code coupled to the STAN5 one for the boundary layer. The losses are calculated by momentum scanning - Stewart’s method. The problem is quasi-steady since the time scale in turbine blade flows is of the order of milliseconds, while in the deposition the data indicate slow growth rates with time scales of the ordr of hours. The particle deposition calculation is based on a turbulent diffusion model proposed by Yau and Young (18) and the particle characteristics refer to ash. The main parameters calculated are the new thickness distribution, the throat blockage, the aerodynamic losses and the transition point. The paper comments on the cleaning process based on these results.

Modern turbine cascades are usually being optimized for minimum total pressure losses. Gas turbines, however, operating in dirty environments or using coal–derived fuels need cascades that minimize the deposition, erosion and corrosion (DEC) implications of the particle–laden gas. This can be achieved by altering certain geometrical key–parameters of cascades and blades which influence the particle deposition rate, while keeping the inlet and outlet velocities and angles fixed. Since reference cascades have already been optimized for minimum aerodynamic losses, the associated loss increase penalty is accounted for. Two stator and two rotor cascades were optimized by a penalty function method. The results suggest that solid particle deposition rates can be minimized by as much as 40 per cent while keeping profile losses to acceptable limits in both stator and rotor cascades for the particle size range 0.1 to 1 μm.