Optimization of the pitch to chord ratio for a cascade turbine blade in wet steam flow

Abstract

• Optimization by GA is used to gain the suitable pitch to chord ratio for a blade. • WF, ADR, MO, PL, and IE at the exit of the cascade turbine blade are the objectives. • A pitch to chord ratio of Pi/AC = 0.76 is suggested. • The modified Zweifel coefficient for wet steam flow in the cascade is proposed C Z F = 0.62 . • The wetness and radius decrease 3.59% and 1.94%, and the momentum increases 7.28%. This study has used shape optimization by the genetic algorithm to gain the suitable pitch to axial chord ratio for a cascade turbine blade. The innovation of the present paper is the modification of the Zweifel coefficient for the wet steam flow passing through the steam turbine cascade. Wetness fraction (WF), average droplet radius (ADR), momentum (MO), pressure loss (PL), and isentropic efficiency (IE) at the exit of the cascade turbine blade in wet steam flow are selected as the objective functions. The ultimate goal was to minimize the wetness fraction, average droplet radius at the outlet of the blade, and pressure losses of the passage and maximize the efficiency and momentum at the outlet together. The Navier-Stokes equations, S S T k - ω turbulence model, and the Eulerian-Eulerian approach are applied for modeling the condensing flow. The agreement gained between the numerical results and the experimental results is satisfactory. A pitch to axial chord ratio of Pi/AC = 0.76 is suggested, and the modified Zweifel coefficient for wet steam flow in the cascade is proposed C Z F = 0.62 . In the optimal case, the wetness fraction and the average droplet radius at the outlet decrease 3.59% and 1.94%, respectively, and the momentum increases 7.28%. In addition, the optimal case compares with original case, the isentropic efficiency decreases 2.48% and the pressure losses increases 2.15%.