A Study of the Effect of Blade Count on Efficiency Using 3D CFD for High Pressure Steam Turbines

The selection of stationary blade count for a steam turbine is closely related to efficiency and manufacturing costs. In this study, the effect of blade count on blade efficiency was examined by CFD analysis. The analyzed model is the steam path of a single stage, including stationary and moving blades to understand thermodynamic and aerodynamic phenomenon of the interstage section. Three cases with 40, 60 and 80 stationary blades and 56 moving blades were used as steam path models. These blades were designed by the in-house systems with free vortex concept for a high pressure turbine. It was shown that the throat area of the stationary blades induced by the variation of blade count affects velocity coefficient (Cv) and flow coefficient (Cq). The mass flow averaged Cv and Cq by 3-dimensional CFD analysis, which considers end wall loss, were calculated. From this result, averaged Cv and Cq tended to decrease as the count of stationary blade increased. This tendency was due to stagnation pressure loss distribution. According to analyses of profile loss and end wall loss, it was confirmed that profile loss decreased as blade count decreased, whereas end wall loss increased but was insignificant compared to profile loss.