Optimisation of a low-pressure multistage steam turbine towards decreasing the wetness losses and aerodynamic losses

Abstract

Aerodynamic losses and wetness losses are two crucial factors which contribute to the decrease in the efficiency of wet-steam turbines. In this study, the response surface method is used to optimise the final three stages of a low-pressure steam turbine in consideration of the combined influences of these losses. The selected optimisation variables are the stagger angles and the blade profile stacking lines along the spanwise direction of the stators in these stages. Results show that the pressure balance in the final three stages is changed by optimising the stagger angles, thus facilitating the redistribution of supercooling degrees. As a result, both non-equilibrium thermodynamic loss and droplet diameter are reduced, and the wetness losses are decreased by 20.71%. Moreover, the method of limiting the wetness losses by adjusting the stagger angles of the low-pressure steam turbine is summarised. The optimisation of the profile stacking lines can improve the reaction degree distribution, reduce the boundary layer separation and limit secondary losses. Consequently, the aerodynamic efficiency is enhanced, and the supercooling and the outlet velocity are altered, thereby shrinking the primary and secondary droplets considerably. The aerodynamic losses are reduced by 0.52%, and the wetness losses are further lowered by 9.48%.