Experimental studies on aerodynamic performance and unsteady flow behaviors of a single turbine stage with variable rotor-stator axial gap: Comparisons with time-accurate numerical simulation

This paper describes experimental results from detailed measurements of aerodynamic performance of a single stage in the turbine test rig of Iwate University, focusing on effects of the rotor-stator axial gap in the turbine stage. The measurements using a 5-hole Pitot tube provide time-averaged flow information such as stagnation pressure distributions and velocity vectors behind the stator as well as the rotor. Time-accurate three-dimensional flow analyses are also made in this study using an in-house N-S code. Realistic flow analyses are achieved in terms of blade-count ratio only by adding one stator vane, resulting in 3:4 blade-count ratio for the present simulation. Aerodynamic characteristics at the exits of the stator as well as the rotor for three axial gap cases are examined in detail through the experimental data and the numerical results. It follows that the increase in the axial gap gives rise to small increment in exit flow angle from the stator, seemingly affecting the flow structure near the hub as well as tip regions around the rotor blades. Furthermore, the turbine stage efficiency slightly decreases with the axial gap enlargement.