Aerodynamic performance change of exhaust passage in steam turbine under low-load conditions

Abstract The exhaust passage is a passage which connect the exhaust port of steam turbine to the inlet of condenser. With the increase of new energy power generation, the coal-fired power units of greater capacity are demanded to participate in peak load regulation, so the steam turbine usually operates under low-load conditions. However, there are lack of literatures that comprehensive analysis aerodynamic performance of exhaust passage under low-load conditions. So in this paper, an exhaust passage coupling with the whole last-stage was numerically simulated by CFX software. The k-ω SST turbulence model and phase transformation model considering the spontaneous condensation flow of wet steam were used. The results show that the inlet swirl flow intensity of exhaust passage increases with the decrease of load. At the 10% turbine heat acceptance(THA) condition, the swirl angle which is more than 90° hold the range of 0% - 64% in blade height. Under low-load conditions, there are six different types of reverse vortices increasing the energy loss of exhaust passage. The total pressure drop of exhaust passage reaches to the maximum of 1671.24 Pa at 10% THA condition. Below the 50%THA condition, the static pressure recovery coefficient cannot be used as the indicator for evaluating the aerodynamic performance of exhaust passage.