Heat Transfer Coefficients of Film Cooling on a Rotating Turbine Blade Model-Part I: Effect of Blowing Ratio

Experimental investigations were performed to measure the local heat transfer coefficient (h(g)) distributions of film cooling over a flat blade under both stationary and rotating conditions. Film cooling was via a straight circular hole of 4 mm in diameter located in the middle section of the blade angled 30 deg along the streamwise direction and 90 deg along the spanwise direction. The Reynolds (Re-D) number based on the mainstream velocity and the film hole diameter was fixed at 3191, and the rotating speed (omega) was either 0 rpm or 800 rpm; the film cooling blowing ratios ranged from 0.4 to 2.0, and two averaged density ratios of 1.02 and 1.53 were employed with air and carbon dioxide (CO2) as the coolant, respectively. Thermochromic liquid crystal was used to measure the solid surface temperature distributions. Experimental results showed the following: (1) In the stationary case, the blowing ratio has a significant influence on the nondimensional heat transfer coefficient (h(g)/h(0)) especially in the near hole region. (2) The film trajectory in rotation had an obvious deflection in the spanwise direction, and the deflection angles on the suction surface are larger than those on the pressure surface. This was attributed to the combined action of the Coriolis force and centrifugal force. (3) In the rotating case, for CO2 injection, the magnitude of heat transfer coefficient on the pressure surface is reduced compared with the stationary case, and the blowing ratio has smaller effects on h(g)/h(0) distribution. However, on the suction surface, the heat transfer coefficient at x/D < 1.0 is enhanced and then rapidly reduced to be also below the stationary values. For air injection, rotation also depresses the h(g)/h(0) for both the pressure and the suction surface. (4) The density ratio shows a considerable effect on the streamwise heat transfer coefficient distributions especially for the rotating cases.