Influence of Near Hole Pressure Fluctuation on the Thermal Protection of a Film-Cooled Flat Plate

Pulsation of film cooling jets in turbines is driven by the near hole pressure fluctuation caused by deterministic interaction of stator/rotor blade rows. Jet pulsation is characterized by the coolant near hole reduced frequency ≅^c and the pulsation amplitude coefficient ≅. Computational requirements for the utilization of a novel experimentally anchored near hole jet model for performing a computationally efficient parametric study of quasi-steady jet pulsations are introduced. Fluctuation of near hole pressure is simulated by setting a time-varying signal of static pressure for the outlet boundary condition of a film-cooled flat plate configuration. It is observed that the fluctuation of near hole pressure influences the blowing ratio hence the thermal protection downstream of the injection site. For a low mean blowing ratio (BR = 0.75), low-medium pulsation frequencies (≅^c ≅ 0.10) are found to be slightly detrimental to the thermal protection versus a steady injection. On the contrary, for high pulsation frequencies (≅^c ≅ 0.17), the thermal protection becomes better due to periodic jet disintegration into the wall surface caused by a higher level of transverse kinetic energy of the jet pulse. In addition, the overlapping of jet pulses appears to help the constant temporal spreading of coolant over the wall surface. For a higher mean blowing ratio (BR = 1.25), jet pulsation enhances jet lift off so that the thermal protection is in general worse compared to a steady injection.