چكيده به لاتين
In this study, the film-cooling performance of an axial turbine blade is evaluated experimentally using the steady state heat transfer method. The blade geometry used by Von Karman Institute (VKI) is selected for this study. Six rows of circular holes are distributed on the blade surface; three rows on the leading-edge region, two rows on the suction surface and a row of holes on the pressure surface. The blowing ratio and incidence angel are ranged from 0.2 to 1.2 and -10 to +10 degrees, respectively. The free stream turbulence intensity and coolant air density ratio are constant and equal to 1.4% and 0.86, respectively. Experiments are performed at Reynolds numbers ranged between 100000 to 250000 based on the free stream velocity and the blade chord length. The most important parameters of this study are the film-cooling effectiveness, convection heat transfer coefficient with and without film-cooling, the Nusselt to Reynoldsnumber ratio and Net Heat Flux Reduction (NHFR). The results reveal that increasing the blowing ratio improve the film-cooling effectiveness of the pressure surface. However, the best performance of film-cooling on the suction surface is obtained at the blowing ratio of 0.6 and more enhancement of the blowing ratio, decreases the cooling effectiveness due to the convex geometry of the suction surface and injected flow separation. Around the blade leading-edge region, not a considerable augmentation in film-cooling effectiveness happens due to the less momentum carried by the fluid particles within the mainstream. In addition, results provided to clearly recognize locations of possible separation and reattachment on the leading-edge region. Also, it is shown that increasing the number of the cooling hole rows is accompanied by 12 percent augmentation in the cooling efficiency. Results show that incidence angel has a considerable effect on the cooling performance of the leading-edge region. Changing the incidence angel dictates a change in the stagnation line position. The incidence angle of -5 degrees is recognized as the best incidence angel at which an augmentation of 16% is occurred on the suction surface while there is not a considerable loss in pressure surface cooling effectiveness. The relation of Nusselt and Reynolds numbers are evaluated in this study and it is achieved as 𝑁𝑢 ∝ 𝑅𝑒0.8, which indicates the turbulence structure of boundary layer. The 𝑁𝑢 ⁄ 𝑅𝑒0.8 curves of different operating conditions are derived and their coincidence shows the independency of aerodynamic and thermal boundary layers from the test operating condition. Finally, the Net Heat Flux Reduction (NHFR) is calculated which proves the positive effect of film-cooling on the turbine blade surface. Keywords: Axial Turbine Blade, Film-cooling Effectiveness, Blowing Ratio, Incidence Angle, Heat Transfer Coefficient, Net Heat Flux Reduction (NHFR).
