The film cooling effectiveness on a low-speed stationary cascade and the rotating blade has been measured by using a heat-mass transfer analogy. The film cooling effectiveness on the suction surface of the rotating blade fits well with that on the stationary blade, but a low level of effectiveness appears on the pressure surface of the rotating blade. In this paper, typical film cooling data will be presented and film cooling on a rotating blade is discussed.

The effects of the three-dimensional flow field on the heat transfer and the film cooling on the endwall, suction and pressure surface of an airfoil were studied using a low speed, fully annular, low aspect h/c=0.5 vane cascade. The predominant effects that the horseshoe vortex, secondary flow, and nozzle wake increases in the heat transfer and decreases in the film cooling on the suction vane surface and the endwall were clearly demonstrated. In addition, it was demonstrated that secondary flow has little effect on the pressure surface. Pertinent flow visualization of the flow passage was also carried out for better understanding of these complex phenomena. Heat transfer and film cooling on the fully annular vane passage surface is discussed.

Direct numerical simulations of transitional flow in a rectangular duct of cross-sectional aspect ratio A ≡ s/h = 1-9 (s and h being the duct half span and half height, respectively) have been performed in the Reynolds number range Re ≡ u b h/ν = 650-1500 (u b and ν being the bulk velocity and the kinematic viscosity, respectively) in order to investigate the dependence on the aspect ratio of spatially localized turbulence structures. It was observed that the marginal Reynolds number Re T for sustaining turbulence monotonically decreases from Re T = 730 for A = 1 (square duct) with increasing aspect ratio and for A = 5 it nearly attains a minimal value Re T ≈ 670 which is consistent with the onset Reynolds number of turbulence in a plane channel (A = ∞). Marginally turbulent states consist of localized structures which undergo a fundamental change around A = 4. At marginal Reynolds numbers turbulence for A = 1-3 is streamwise-localized similar to turbulent puffs in pipe flow, while for A = 5-9 turbulence at marginal Reynolds numbers is also localized in the spanwise direction, similar to turbulent spots in plane channel flow. This structural change in marginal states is attributed to the exclusion of turbulence from the vicinity of the duct side-walls in the case of a wide duct with A 4: here the wall shear rate on the side-walls is so low (and thus friction length is so long) that a self-sustaining minimal flow unit of streamwise vortices and streaks is larger than the duct height and, therefore, it cannot be accommodated.