# Effects of Bulk Flow Pulsations on Film Cooling with Two Sister Holes
## 5 Conclusions  
The mainstream of film cooling can be disturbed by several factors. The specific goal of the current study is to investigate the effects of the main flow pulsation on the film cooling performance for the triple holes system in order to help for making better cooling design of the gas turbine engines. Film cooling in a triple hole system was numerically simulated in an LES. Contours of \(\eta\) on the wall and cross-sectional views of the mean dimensionless temperature contours for the single-hole and triple-hole systems showed that the triple-hole configuration exhibits better film cooling performance for 0, 2, 16, and 32 Hz pulsations. In the triple-hole system, increasing the frequency to 32 Hz or Strouhal number from 0 to 1.6085 decreased the film cooling effectiveness to a lesser extent compared with the single-hole system. As the frequency increased from 0 to 2, 16, and 32 Hz in the single-hole, laterally averaged \(\eta\) decreased by approximately 11%, 12%, and 45%, respectively, and this trend was confirmed in the experimental data. In the triple hole, increasing the frequency  
Figure 18: Q-criterion contours (level: 80,000).  
from 0 to 2, 16, and 32 Hz decreased the spanwise-averaged film cooling effectiveness by approximately 4%, 5%, and 39%, respectively. The film cooling effectiveness was always higher in the triple-hole system because of the generation of an anti-CRVP. Furthermore, increasing the pulsation frequency or Strouhal number increased the ratio of \(\eta_{m,\ triple\ hole}\) to \(\eta_{m,\ single\ hole}\), indicating that at higher pulsation frequencies or Strouhal numbers in the main flow, the triple holes were more effective for film cooling compared with the single hole. Contours of time-averaged velocity magnitude in sister holes showed that the flow was more developed than that in the main hole, even at 32 Hz pulsation. This indicated that the sister holes improved the film cooling effectiveness through the generation of an anti-CRVP and by increasing the \(L/D\) ratios. Q-contours for triple hole at 0 and 32 Hz showed smaller hairpin and jet shear layer vortices compared with those for the single-hole system, indicating a weakened CRVP. In the contours of the instantaneous film cooling effectiveness, the horseshoe vortex was visible periodically at 32 Hz pulsation because this vortex was generated when the vortex in the boundary layer of the main flow was blocked by strong coolant injection and roll-up. This paper only covered the cylindrical hole, however, the effects of the main flow pulsations on film cooling for the shaped hole such as the forward expansion hole will be covered in future studies. Moreover, the effects for the two sister holes positioned more downstream of the primary hole and the optimized length between the sister hole and the primary hole will be investigated to obtain the best film cooling performance. For the parametric study, the CFD results of this study could be used as the baseline.  
Simulations, S.I.B.; analysis, S.I.B. and J.A.; writing, S.I.B. and J.A.; supervision, J.A. All authors have read and agreed to the published version of the manuscript.  
No external funding.  
Not applicable.  
Data is contained within this article.  
No conflict of interest.