Non-axisymmetric endwall modeling for large meridional expansion turbines based on pressure field distribution

To improve large meridional expansion turbine side area of pneumatic and heat transfer performance, based on the large meridional expansion turbine upper wall static pressure distribution in detail, non-axisymmetric endwall modelling technology was employed for eight kinds of asymmetric design for a 1.5 magnitude large meridional expansion level 2 of a turbine upper wall, by combining the Bezier curve with a sine curve of trigonometric function; and the SST（shear stress transfer） turbulence model was used to solve the RANS（Reynolds-averaged Navier-Stokes equations） equations of end wall before and after the modelling of the flow and heat transfer characteristics research. Results showed that the non-axisymmetric design of the upper endwall of a large meridional expansion turbine can effectively improve the distribution of transverse pressure difference in the blade passage at the upper end of the turbine. The total pressure loss at the outlet can be reduced by bulking the upper endwall pressure surface in the channel. When the bulking amplitude is 5% of the S2 blade height, the total pressure loss at the outlet can be reduced by 1.1% at most. The heat load of the casing and blade can be reduced by hollow modeling on the suction and pressure surfaces of the upper end wall. When the sag amplitude is 5% of the blade height of S2, the thermal load of the casing and blade can be reduced by about 3.1% and 2.8% respectively at most.