A study of the flow in a transonic turbine stage with long and strongly twisted rotor blades is presented. The focus is on the flow in the near tip region of the blade-to-blade passage of the rotor. The flow has been modelled experimentally in a transonic wind tunnel and numerically by means of 2D and 3D Navier-Stokes equation solvers.

The profiles of the rotor cascades are characterized by law turning angles and a high-velocity exit flow. Detailed flow measurements have been carried out and analysed. A comparison has been made between the experimental and numerical results, and is discussed in detail.

The design and test data of the flow through the upper sections of the span are presented. The effects of the tip leakage flow are evaluated and the three-dimensional patterns of the main flow are estimated. Other points of interest are the results of 3D Navier-Stokes analysis of the stage flow as compared to 2D simulations and wind tunnel experiments, together with the question of the limitations of the individual methods as they all use approximations to the actual flow in the turbine stage.

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