Numerical investigation on flow characteristics in steam turbine low pressure cylinder and LPEH under different volume flow rate conditions

A numerical investigation on full-three-dimensional steady viscous flow fields in the last three stages and low pressure exhaust hood (LPEH) of a steam turbine was conducted using the commercial computational flow dynamics software CFX. The flow fields in the last three stages were analyzed in detail. The results show that a separation caused by the adverse pressure gradient occurs at the hub section near the trailing edge of the last stage rotor at 40% of the design mass flow rate. Moreover, a separation caused by the negative attack angle occurs at the tip section near the leading edge of the last stage rotor at 30% of the design mass flow rate. A separation also caused by the negative attack angle occurs near the leading edge of the last stage stator at 10% of the design mass flow rate. In addition, the absolute outlet flow angle of the last stage rotor at the tip section increases with the decrease in volume flow rate, and the radial location of the reverse flow can be determined by the turning point of the absolute outlet flow angle in the blade radial direction.