The Effect of Vortex Shedding on the Unsteady Pressure Distribution Around the Trailing Edge of a Turbine Blade

The wakes behind turbine blade trailing edges are characterized by large-scale periodic vortex patterns known as the von Karman vortex street. The failure of steady-state Navier–Stokes calculations in modeling wake flows appears to be mainly due to ignoring this type of flow instabilities. In an effort to contribute to a better understanding of the time-varying wake flow characteristics behind turbine blades, VKI has performed large-scale turbine cascade tests to obtain very detailed information about the steady and unsteady pressure distribution around the trailing edge of a nozzle guide vane. Tests are run at an outlet Mach number of M_2,is, = 0.4 and a Reynolds number of Re_C = 2 × 10⁶. The key to the high spatial resolution of the pressure distribution around the trailing edge is a rotatable trailing edge with an embedded miniature pressure transducer underneath the surface and a pressure slot opening of about 1.5 deg of the trailing edge circle. Signal processing allowed differentiation between random and periodic pressure fluctuations. Ultrashort schlieren pictures help in understanding the physics behind the pressure distribution.