Influence of the Hole Length-to-Diameter Ratio on Film Cooling With Cylindrical Holes

Abstract

Film cooling experiments were conducted to investigate the effects of coolant hole length-to-diameter ratio on the film cooling effectiveness. The results from these experiments offer an explanation for the differences between the film cooling results for cylindrical hole injection configurations previously reported by Goldstein et al. (1974), Pedersen et al. (1977), and Sinha et al. (1991). The previously reported injection configurations differed primarily in coolant hole length-to-diameter ratio. The present experiments were conducted with a row of cylindrical holes oriented at 35 deg to a constant-velocity external flow, systematically varying the hole length-to-diameter ratios (L/D = 1.75, 3.5, 5, 7, and 18), and blowing rates (0.52 ≤ M ≤ 1.56). Results from these experiments show in a region 5 ≤ X/D ≤ 50 downstream of coolant injection that the coolant flow guiding capability in the cylindrical hole was apparently established after five hole diameters and no significant changes in the film cooling effectiveness distribution could be observed for the greater L/D. However, the film cooling effectiveness characteristics generally decreased with decreasing hole L/D ratio in the range of 1.75 ≤ L/D ≤ 5.0. This decrease in film cooling performance was attributed to (1) the undeveloped character of the flow in the coolant channels and (2) the greater effective injection angle of the coolant flow with respect to the external flow direction and surface. The lowest values of film cooling effectiveness were measured for the smallest hole length-to-diameter ratio, L/D = 1.75.

Heat Transfer and Film Effectiveness Study on a Pitchwise Curved Surface with Unsteady Wake Interaction

“…The inclination angle (α) was 35°, the compound angle (β) was 0°, and the L/D was 8. A higher L/D reduces the premature lift-off [9] . The p/D was maintained at 3 for the 5 film cooling holes.…”

“…Some of the investigations on flat plate with streamwise inclination of discrete holes were performed by Eriksen and Goldstein [1], Goldstein et al [2] , Goldstein and Yoshida [3] , Sinha et al [4] , Bell et al [5] , Hay et al [6] , Liess [7] , Pedersen et al [8] , Lutum and Johnson [9], Goldstein and Taylor [10] , and Amari et al [11] . The effects of film hole geometry and density ratio were studied by Goldstein et al [2] .…”

Effect of hole imperfection on adiabatic film cooling effectiveness

“…They investigated the influence of a plenum on film cooling and found that the plenum geometry has an effect on the film cooling effectiveness, which depends on the injection hole length and streamwise hole angle. The effect of the hole length in the film cooling process was demonstrated in the study of Lutum and Johnson (1998). They reported that the length to diameter ratio larger than 7, has a small effect on the film cooling effectiveness.…”

Computational Study of Parameters Affecting Turbulent Flat Plate Film Cooling

“…Some of the most important parameters which have gained much of the researchers' attention are: cooling jet injection angle [6], compound injection angle [7,8], blowing ratio [9,10], spanwise and streamwise hole spacing [11,12], length of the cooling jet [13,14,15,16,17,18], boundary layer thickness [19], convexity or concavity of the wall [19], and turbulence [15,20,21,22].…”