Steam turbine high-pressure reaction stages;new 3D vortices breakdown and airfoil optimization method

Abstract

3D airfoil optimization is a widely used and beneficial method for upgrading axial turbines. However, the reviewed literature shows that it does not yield significant efficiency gains in high-pressure reaction stages of steam turbines. We concluded that the followed optimization approaches were not proper enough. In this paper, we used numerical simulations to study the structure of longitudinal vortices in these stages and find main phenomena causing aerodynamic losses. After that, we perused the existing 3D airfoil optimization methods to affect these phenomena significantly. In this way we planned and used an optimization approach to weaken the phenomena which are main sources of aerodynamic losses. We found that besides the well-known secondary vortices, there are two influential vortices called “Mixing vortex” and “Incidence vortex”, which are investigated in detail. The mixing vortex is the largest longitudinal vortex in a high-pressure steam turbine stage. To enhance the aerodynamic efficiency and reduce these longitudinal vortices, we used a combination of lean, twist and “Endwall Section Scaling (ESS)” which is introduced in this paper. To capture the effect of longitudinal vortices more accurately, the optimization is applied to a 1.5-stage HP turbine. In the optimized configuration, the efficiency of the 1.5-stage HP turbine increases by 0.61% while mass flow rate and pressure ratio are kept constant.