No abstract

Relatively few studies have examined the effects of pulsating unsteadiness in turbine cooling blades. This unsteadiness can be a result of compressor blades and vane interaction. In addition, there is a particular lack of data of full turbine blades at various angles of attack. The effects of pulsation frequency (f = 2 Hz, 50 Hz, and 100 Hz) and the angle of attack (α = 0°, 15°, and 30°) on the film cooling effectiveness of a row film jet at the leading edge of a modified NASA C3X blade for two blowing ratios (M = 0.5 and 1.0) in comparison with the steady state experimentally investigated on pressure and suction sides of the blade and the flow field are obtained by simulation. Three-dimensional transient Reynolds-averaged Navier–Stokes equations coupled with the shear stress transport turbulence model (SST k − ω) are used in this research. Square waves are considered to pulse the injection air. Results show that the distribution of the instantaneous film cooling effectiveness is affected by frequency, angle of attack, blowing ratio, and curvature of the blade. With an increase in the angle of attack and the pulsing frequency, the averaged film cooling effectiveness increased. Pulsation and angle of attack have different effects on the performance of the injection jet toward the pressure and suction sides of the blade. Mixing of injection air with the mainstream at the pressure side is more than that at the suction side. Under certain conditions, the averaged film cooling effectiveness of pulsation flow is greater than the steady jet.

In this paper, the influence of pulsating air on film cooling of a flat plate at different frequencies and blowing ratios are experimentally and numerically investigated. Square wave pulsed flow is generated at four frequencies of 2, 10, 50, and 100 Hz corresponding to Strouhal numbers of 0.00254, 0.0127, 0.0636, and 0.1271, respectively, and at five blowing ratios of 0.5, 1, 1.5, 2.4, and 3. Reynolds-averaged Navier−Stokes equations are resolved to analyze the coolant film effectiveness based on parameters set in the experiments. The [Formula: see text] model used for turbulent modeling. The obtained results showed that the performance of pulsating cooling decreases with increasing of blowing ratio at the same flow as steady state conditions. The difference between numerical and experimental values for the centerline film effectiveness shows good adaptation at the distances of the injection hole downstream. The lift-off of the local jet increased under pulsation. Increasing the pulse frequency increases the overall efficiency of film cooling. The maximum mean centerline pulsating film cooling effectiveness is obtained at Strouhal number of 0.0636 and a blowing ratio of 0.5, and the minimum value is for Strouhal number of 0.00254 and a blowing ratio of 3. For pulsed flow, the maximum discrepancy of the mean centerline film effectiveness between experimental and numerical results was 17.82%.