The unsteady structure of simulated turbine film cooling flow from PIV

Unsteady turbine film cooling flows are subjected to free stream disturbances which exceed those of a fully turbulent boundary layer. Hot wires, cold wires, and thermocouples have in the past been used to obtain local, time resolved point measurements of velocity, temperature and mixing. The structure of the flow and its interaction with free stream structures remains largely hidden. Two-color, double pulsed, PIV (Particle Image Velocimetry) was used to investigate simulated turbine film-cooling flows with high free stream turbulence and wake passing. High resolution (3000x2000 pixels), instantaneous, velocity distributions obtained by CCD camera have been compared against those obtained from 35mm film digitized at 2700 ppi resulted in realizations with similar spatial resolution. Averages of I to 30 instantaneous PIV velocity measurements have been compared against simulated turbine film cooling flow velocity profiles measured by hot wire. The resulting PIV velocity profile measurements were mostly within the envelope of the mean and nns velocity measurements of the hot wire. The PIV images allow instantaneous estimates of the shear layer development, vertical cooling jet film spread, turning, and interactions with the free stream turbulence. Instantaneous vorticity, and dissipation distributions have also been obtained. The lateral jet spread of the film at the wall was measured with liquid crystals and thermocouples and compared with the vertical PIV spread. The centerline vertical film jet spread, turning angle, and shear layer growth has been characterized from the PIV realizations as a function of blowing ratio, Reynolds number, periodic forcing amplitude, frequency, and free stream turbulence.