Investigation of the unsteady rotor flow field in a single HP turbine stage

Kurzfassung

Within a European project a high-pressure turbine stage was investigated at DLR, Goettingen. The investigations consisted mainly of experiments carried out in the windtunnel for Rotating Cascades (RGG), but also some numerical work was 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 and averaged 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 unsteady flow vectors from the experiment are compared with results from a numerical computation using the Navier-Stokes code "TRACE-U" which allows the computation of the unsteady flow field. Steady and unsteady flow quantities were extrapolated to the blade surfaces to visualize the unsteady Mach number distributions and the traces of the wake near the rotor blade suction and pressure sides. A comparison of the wake trajectories from the concentration measurements with surface hotfilm measurements and numerical computations 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.