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

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,SSTk -omega turbulence model, and the EulerianEulerian 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 CZF = 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%.

Automated summary

This study used genetic algorithm for shape optimization and obtained the suitable pitch to axial chord ratio for a cascade turbine blade. The modification of the Zweifel coefficient was innovatively employed to improve the performance of wet steam flow passing through the steam turbine cascade.