Stage Tests, Part II. Investigation of the Unsteady Rotor Flow Field by Laser-2-Focus Velocimetry

Kurzfassung

In the windtunnel for Rotating Cascades of the DLR Göttingen (RGG) the IMT Area 3 Turbine stage was investigated with the help of a Laser-2-Focus anemometer (L2F). Investigations were performed for two stator-rotor axial gaps and two coolant flow rates i.e. four test configurations. In order to determine the unsteady flow field, measurements had to be carried out at 16 circumferential rotor positions covering one rotor pitch at each stator position. The measurements at several circumferential stator positions had to cover at least one stator pitch. Axial measurement locations reached from the stator exit through the rotor to a downstream measurement plane. All measurements were restricted to the mid section of the meridional flow path. The L2F-device was used 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 technique is shortly discussed. Measurement results are presented as absolute flow values averaged over the rotor pitch, thus depending only on the stator position, and as relative flow values averaged over a stator pitch and therefore depending only on the rotor position. Mean flow values could be gained by doubly averaging over stator and rotor pitch. The unsteady flow quantities are extensively presented for the test configuration with coolant and narrow stator-rotor gap. Unsteady flow vectors and turbulence intensities could be related at 16 time instants to the wake development made visible by coolant concentration. Steady and unsteady flow quantities were extrapolated to the blade surfaces to visualize the unsteady Mach number distributions and the traces of the wake trajectories near the rotor blade suction and pressure sides