ENDWALL AND UNSTEADY-FLOW PHENOMENA IN AN AXIAL TURBINE STAGE

Detailed experimental and numerical studies have been performed in a s ubsonic, axial-flow turbine stage to investigate the secondary flow fi eld, the aerodynamic loss generation, and the spanwise mixing under a stage environment. The experimental study includes measurements of the static pressure distribution on the rotor blade surface and the rotor exit flow field using three-dimensional hot-wire and pneumatic, probe s. The rotor exit flow field was measured with an unsteady hot-wire pr obe, which has high temporal and spatial resolution. Both steady and u nsteady numerical analyses were performed with a three-dimensional Nav ier-Stokes code for the multiple blade rows. Special attention was foc used on how well the steady multiple-blade-row calculation predicts th e rotor exit flow field and how much the blade interaction affects the radial distribution of flow properties at the stage exit. Detailed co mparisons between the measurement and the steady calculation indicate that the steady multiple-blade-row calculation predicts the overall ti me-averaged pow field very well. However, the steady calculation does not predict the secondary flow at the stage exit accurately. The curre nt study indicates that the passage vortex near the hub of the rotor i s transported toward the midspan due to the blade interaction effects. Also, the structure of the secondary flow field at the exit of the ro tor is significantly modified by the unsteady effects. The time-averag ed secondary flow field and the radial distribution of the flow proper ties, which are used for the design of the following stage, can be pre dicted more accurately with the unsteady flow calculation.