Within a European project a high-pressure turbine stage was investigated at DLR, Göttingen. The investigations consisted primarily of experiments carried out in the windtunnel for Rotating Cascades (RGG), but some numerical work was also performed.
Detailed measurements were carried out at mid section of a turbine rotor using a Laser-2-Focus device which served as a velocimeter measuring 2D-velocity vectors and turbulence quantities and as a tool to determine the concentration of coolant ejected at the trailing edge of the stator blades. The measurement of coolant concentration downstream of the stator and inside the rotor provided a detailed picture of the stator wake development and its interaction with the moving rotor. Axial measurement locations reached from the stator exit through the rotor to a downstream measurement plane. Measurement results are presented as instantaneous flow values. Unsteady flow vectors and turbulence intensities could be related at 16 time instants representing one rotor blade passsing period to the wake development made visible by the coolant concentration. The measured unsteady flow vectors and unsteady pressures, measured with semi-conductor pressure transducers, are compared with results from a numerical calculation using the Navier-Stokes code “TRACE-U” which allows the computation of the unsteady flow field. The measured steady and unsteady flow quantities served to validate the Navier-Stokes code. A comparison of the wake entropy trajectories outside the blade boundary layers and at the wall gives an impression of the lag between the arrival time of the wake in the freestream near the blade surface and the time the boundary layer quantities at the blade surface itself are affected.
