A Parametric Study on the Effect of Sister Hole Location on Active Film Cooling Flow Control

Abstract

This paper presents an investigation on the effect of sister holes on film cooling. The proposed technique surrounds a primary injection hole by two or four smaller sister holes to actively maintain flow adhesion along the surface of the blade. A numerical evaluation using the realizable k-ε turbulence model led to the determination that the use of sister holes significantly improves adiabatic effectiveness by countering the primary vortical flow structure. Research was performed to determine the optimal hole configuration, arriving at the conclusion that placing sister holes slightly downstream of the primary injection hole improves the near-hole effectiveness, while placing sister holes slightly upstream of the primary hole improves downstream effectiveness. On the whole, the sister hole approach to film cooling was found to offer viable improvements over standard cooling regimes.

Numerical Analysis of Film Cooling Performance of Micro Holes and Compound Angle Sister Holes

“…shown in Figure 6.6 a) illustrated that the current results pretty much agree well with the results of Ely and Jubran [65] for the short hole case (L/D = 1.16) whereas the general trend is captured; however, a slight disagreement is seen at (X/D > 10). The difference becomes more pronounced between the current results and the results of Ely and Jubran [64] a good agreement with Ely and Jubran [64], [65] in which the general trend is well captured.…”

“…Additionally, Figure 6.15 at X/D= 3 and 5, illustrates that for all studied CAUSH, the coolant core is attached to the surface due to prominently displayed ACRVP; however, more mixing is shown, which leads to a decrease on the performance. Ely and Jubran [64], [65], as well as Wu et al [10], found the same flow structure results of 0° CAUSH at M=0.5 whereas they reported the ACRVP produced by sister holes is efficiently controlling the CRVP of the main hole.…”

“…Also, all of those studies have examined sister holes that are only streamwise injected to the plate surface at α ≈ 35°. Therefore, as a part of validation of the numerical results, the current computational results of the 0° compound angle upstream sister holes are compared against the numerical results of Ely and Jubran [64], [65] for the upstream sister holes case; that is only streamwise injected at α = 35°, at blowing ratio of M=0.5 and D.R=1.2, as shown in Figure 6.6 a) and b). The centerline film cooling effectiveness results…”

“…performed by Ely and Jubran[64] [65] documented that optimal film cooling protection of long sister holes (L/D=5) was obtained by placing the sister holes left and right from main hole center, as shown in Figure2.7 c), while the maximum performance for short sister holes (L/D=1.16) was found via employing four active sister holes, placed 0.75D upstream/downstream the main hole. Moreover, Ely and Jubran[65] compared sister holes film cooling performance of long holes; (L/D) ratio= 5[64], with that for the short holes; (L/D) ratio = 1.16, and they concluded that regardless of the length of the sister hols, a notable increase in film cooling effectiveness was found. However, the main difference identified was in the flow structure generated from short holes that tended to have less defined counterrotating vortex pairs[65][64].…”

Effects of chemical reaction caused by cooling stream on film cooling effectiveness

“…However, they are limited by technical difficulties of manufacture. Therefore, Heidmann, Dhungel et al [3][4][5], Ely and Jubran [6] considered the cylindrical holes again, and studied the anti-vortex arrangement in which one primary cooling hole is accompanied by two small side holes. Detailed flow visualization shows that, as expected, the design counteracts the detrimental vorticity of the round hole flow, allowing it to remain attached to the surface.…”