Detailed studies on aerodynamic performance and unsteady flow behaviors of a single turbine stage with variable rotor-stator axial gap

The aim of the present study is to investigate effects of the axial gap between rotor and stator upon the stage performances and flow field of a single axial flow turbine stage. In this paper experimental and numerical studies are performed for three axial gaps by moving the stator vane axially. Five-hole probe measurements are made to obtain total pressure loss and time-averaged flow field upstream and downstream of the rotor blades. In addition, large-scale unsteady threedimensional RANS-based numerical simulation, in which blade-count ratio is almost the same as that of the actual turbine stage, is executed to understand interaction between the stator and the rotor. These results show that overall turbine stage efficiency with the smallest axial gap is the highest among the three gaps. This is because the stator wakes are diffused by expanding axial gap, inducing the growth of the secondary flow near the endwall.