Effect of Pulsed Film Cooling on Leading Edge Film Effectiveness

Abstract

Detailed film effectiveness measurements have been made on a cylindrical leading edge surface for steady and pulsating flows. The film hole is off centered by 21.5 deg from the centerline and angled 20 deg to the surface and 90 deg from the streamwise direction. Two jet-to-cross-flow velocity ratios have been considered: VR=1 and 2, which correspond to blowing ratios of 1 and 2, respectively. The pulsating frequency is 10 Hz and the duty cycle is 50%. Comparisons between film effectiveness with a pulsating film and a continuous film show that for the same blowing ratio, the effectiveness of the film drops by a factor of 2 when the flow is pulsed. Hotwire measurements are made to characterize the pulsating velocity waveform at the exit of the film exit and verify the integrity of the pulse. The variation in the measured surface adiabatic wall temperature over the pulsing duration is very small, suggesting a large thermal inertia that keeps the wall surface largely unaffected by the time scale of the pulsations; this holds true for both blowing ratios tested.

Numerical investigations of pulsed film cooling on an entire turbine vane

“…This result is consistent with previous research of El-Gabry and Rivir [9]. While comparing to the steady flow, the sinusoidal wave pulsed flow decreases film cooling effectiveness at BR ¼ 0.5, but increases film cooling effectiveness and improves film coverage effect at BR ¼ 0.75 and BR ¼ 1.0.…”

“…Ekkad et al [8] used a transient infrared technique to investigate the effects of jet pulsation and DC on film cooling effectiveness and heat transfer on a circular LE, their results indicated that reducing the DCs leads to higher film cooling effectiveness and lower heat transfer coefficients, and the influences of jet frequencies (5 Hz, 10 Hz and 20 Hz) on the film cooling effectiveness and heat transfer coefficient are not important. El-Gabry and Rivir [9] experimentally measured the film cooling effectiveness on a cylindrical LE surface, and compared the cooling effect of steady flow with that of pulsating flow. Their comparison showed that at the same BR, the film cooling effectiveness is reduced by a factor of 2 when the flow is pulsed, and therefore they deemed that it is necessary for further investigation to fully understand the pulsating performances, and to confirm when pulsating can enhance film cooling effectiveness.…”

Optimization of Forcing Parameters of Film Cooling Effectiveness

“…It is clear from the studies above [10][11][12][13][14] that the reported results are not consistent with both positive and negative effects of coolant pulsations on film cooling. Further, in the experimental studies reported in the literature, there is a significant amount of deviation between the desired instantaneous blowing ratio and the actual delivered pulse form.…”

“…They also observed that the pulsed jet outperformed the steady jet with the same time-averaged blowing ratio. El-Gabry and Rivir [12] studied the effect of pulsation on the leading edge film cooling on the same geometry [11], and observed that the film effectiveness of the pulsed cases were lower than that of steady jets with the same time-averaged blowing ratios.…”

Effects of Flow Oscillations in the Mainstream on Film Cooling

“…They reported that three parameters related to pulsation (frequency, blowing ratio, and duty cycle) affect the film cooling performance. El-Gabry and Rivir (2012) investigated the effect of coolant jet pulsation on a leading edge surface experimentally and reported that the film cooling effectiveness was decreased by a factor of 2 compared to that at a steady state [25]. The blowing ratios were 1.0 and 2.0, the frequency of the pulsation was 10 Hz and the duty cycle was set as 50%.…”