Unsteady non-equilibrium condensation flow of 3-D wet steam stage of steam turbine with roughness using sliding mesh method

Abstract

This research develops the non-equilibrium condensation model with sliding mesh technology to solve the unsteady condensing flow inside a 3D wet steam stage of steam turbine with transient rotor-stator interaction. The maximum fluctuation of time-dependent condensation parameters is predicted. The condensation loss and entropy generation considering the off-design operation and rough blades are also evaluated quantitatively. The results showed that the secondary expansion and condensation occur near the rotor trailing edge. At design operation, the time-dependent subcooling fluctuates from −9.81 K to 8.06 K at the maximum fluctuation location. The frozen rotor method over-predicts the expansion and condensation characteristics in the steam turbine stage. Moreover, the maximum relative fluctuation of time-dependent wetness is 37.14% when it changes from 0.022 to 0.048. At off-design operation, the p-T diagram is applied to compare the expansion and condensation processes. The inlet subcooling increases by 40 K, resulting in an increase of 110.34% in outlet wetness. The phase of condensation loss with high off-design inlet subcooling is ahead of that with low off-design inlet subcooling. The fluctuation of time-dependent condensation loss with off-design inlet subcooling is about 102.28 kW. In addition, the back pressure ratio changes from 0.55 to 0.10, resulting in an increase of 190.91% in outlet wetness. The fluctuation of time-dependent condensation loss with off-design back pressure ratio can reach 112.3 kW. Besides, the maximum time-averaged entropy generation and exergy destruction due to the increase of surface roughness can reach 9.37 kJ kg−1 K−1 and 5.71 kW.