Wet steam flow and condensation loss in turbine blade cascades

Abstract

Abstract This study develops a wet steam modelling to solve the phase change process inside the blade cascade of a steam turbine. The comparative study is carried out to understand the impact of the dry gas model and wet steam model on predicting the flow behaviours in a steam turbine. The effect of the cutback of the trailing edge on the flow structure and nonequilibrium condensation is evaluated in blade cascades. The results show that the dry gas assumption without considering the phase change process predicts fraudulently flow separations near the trailing edge to induce oblique waves. The maximum liquid fraction can reach approximately 0.051 based on the wet steam flow modelling. The condensation-evaporation processes in the blade cascades cause a condensation loss of 0.118 MW. The stronger expansion flow is obtained to induce the earlier onset of the homogeneous nucleation process with an increasing cutback of the trailing edge. The 21% cutback of the trailing edge leads to strong flow separations on the suction side to severely deteriorate the flow condition in blade cascades. It suggests that the cutback of the trailing edge by 14% is acceptable to repair damaged blades considering the flow structure, nonequilibrium phase change and condensation loss.