Figures 1 illustrates the local film effectiveness (η) distributions at blowing ratio M = 0.75 for both the pulsed coolant (PF = 10 Hz, DC = 75%) and the continuous coolant, respectively. The film effectiveness distribution clearly shows the coolant jet trajectory. At this blowing ratio, the momentum (momentum ratio I = 0.51) of the coolant is much lower than that of the mainstream. The mainstream (coming from the left) deflects the coolant jet (exiting upward in the spanwise direction, Z, from the film hole). The coolant then travels primarily in the streamwise direction, X, without noticeable spanwise movement for either the pulsed or the continuous flow. The film effectiveness value peaks immediately downstream of the coolant injection location and then decreases due to the coolant’s dissipation as it moves downstream. Compared to the continuous coolant, the pulsed coolant provides greater film coverage (as a result of its broader coverage), which contributes to the higher spanwise-averaged film effectiveness.

Figure 2 presents the effect of coolant pulsation at blowing ratio M = 1.00 on the spanwise-averaged film effectiveness and Frossling number, respectively. The researchers converted the imaging field into the physical arc length (X) from the stagnation line of the leading edge test model and the film hole diameter (d). In this coordinate system, the film hole spans the range between X/d = 3 and X/d = 4, with the hole centerline located at X/d = 3.5. The spanwise-averaged values peak immediately downstream of the injection location for both heat transfer coefficient and film effectiveness, just as they did in the M = 0.75 scenario depicted in the Figure 1 images. As shown, pulsed cases provided higher film effectiveness than did the continuous flow condition—a positive benefit of coolant pulsation. At this blowing ratio, the continuous coolant jet possesses a momentum (momentum ratio I = 0.90) slightly lower than that of the mainstream flow. The pulsed coolant jet, however, exhibits a much smaller (although not zero) momentum when the valves are closed, because the valve timing dictates that some residual coolant will remain in the coolant chamber until the valves open again. This variable momentum characteristic of the pulsed coolant results in higher film effectiveness than continuous flow cases are able to achieve. Likewise, all pulsed cases demonstrate heat transfer coefficients comparable to or slightly lower than those generated in the continuous flow cases—another positive advantage created by the coolant pulsation. Neither the PF nor the DC, however, has much effect on the heat transfer coefficient distribution.