Aerothermal Performance of Streamwise and Compound Angled Pulsating Film Cooling Jets

The quantification of aerothermal loss is carried out for streamwise and compound angled film cooling jets with and without large scale pulsation. This paper reports on the simultaneous measurements of the unsteady pressure and temperature field of streamwise and a 60 deg compound angled film cooling jet, both with a 30 deg surface angle over a flat plate with no pressure gradients. Turbine representative nondimensionals in terms of the geometry and operating conditions are studied. The main flow is heated more than the injected flow to have a temperature difference and hence a density ratio of 1.3, while the blowing ratio is maintained at 2. The entropy change, derived from pressure and temperature measurements, is calculated by using modified reference conditions to better reflect the losses in both the jet and the freestream. The effects of the periodic unsteadiness associated with rotating machinery are simulated by pulsating the jets. These effects are documented through time-resolved entropy change contours. Mass-averaged entropy and kinetic energy loss coefficients seem to be apt quantities for comparing the aerothermal performance of streamwise and compound angled injections. It is observed that the mass-averaged entropy loss of a streamwise jet doubles when it is pulsated, whereas that of a compound angled jet increases by around 50%. It may be conjectured from the measurements shown in this study that streamwise oriented jets suffer most of their entropy losses at the hole exit due to separation, whereas in compound angled jets, downstream thermal mixing between the jet and the freestream is the dominant mechanism.