FILM COOLING CHARACTERISTIC OF DOUBLE-FAN-SHAPED FILM COOLING HOLES

The film cooling performance downstream of a single row of double-fan-shaped film cooling holes in a flat plate have been investigated by experimental measurements and numerical simulation. The entrance and exit of double-fan-shaped holes are comprised of a lateral expansion of 15 degrees from the original simple cylindrical shape with stream-wise inclination of 45 degrees. The width of the exit face to cylinder diameter ratio is 1.5; the length-to-diameter ratio is 4.24 and the pitch-to-diameter ratio is 3. The experimental method used to obtain the adiabatic film cooling effectiveness values and the heat transfer coefficient is a transient narrow band liquid crystal technique. Both film cooling effectiveness and heat transfer coefficient are measured at three momentum ratios (I=0.5, 1, 2) at constant Reynolds number (Re=10000) and free stream turbulence (Tu=2%). The film cooling effectiveness, heat transfer coefficient and Net Heat Flux Reduction (NHFR) are presented for detailed distribution and span-wise averaged values. Discharge coefficients are also measured in the experiment. A commercial package is used to numerically simulate the flow and heat transfer of double-fan-shaped holes; simple cylindrical holes are also simulated for comparison. Numerical simulation use RNG turbulence model with a standard wall function for near wall region. Experimental and Numerical simulation results show that: I) the double-fan-shaped holes present higher discharge coefficient than simple cylindrical holes at respective momentum ratio; 2) the numerical simulation film cooling effectiveness results of double-fan-shaped holes accord well with the experimental results; 3) at measured three momentum ratios, the double-fan-shaped holes demonstrate better film cooling performance (higher NHFR) than simple cylindrical holes, better film cooling expansion on span-wise; 4) the best momentum ratio of double-fan-shaped holes is 0.5.