Large Eddy Simulation of Film Cooling with Triple Holes: Injectant Behavior and Adiabatic Film-Cooling Effectiveness

Abstract

This study investigated the effect of adding two sister holes placed downstream the main hole on film cooling by employing large eddy simulation. Here, film-cooling flow fields from a triple-hole system inclined by 35° to a flat plate at blowing ratios of M = 0.5 and unity were simulated. Each sister hole supplies a cooling fluid at a flow rate that is a quarter of that for the main hole. The simulations were conducted using the Smagorinsky–Lilly model as the subgrid-scale model, and the results were compared with those for a single-hole system for the same amount of total cooling air and same cross-sectional area of the holes. Relative to the single-hole system, the spanwise-averaged film-cooling effectiveness in the triple-hole configuration at M = 1.0 increased by as much as 345%. The subsequent proper orthogonal decomposition analysis showed that the kinetic energy of a counter-rotating vortex pair in the triple-hole system dropped by 30–40% relative to that of the single-hole system. This indicates that the additional sister holes promoted the suppression of the mixing of the coolant jet with the mainstream flow, thus keeping the temperature of the latter low. Cross-sectional views of the root-mean-square temperature contours were also analyzed; with the results confirming that the effect of the sister holes on the jet trajectory greatly contributes in promoting film-cooling effectiveness as compared to the effect of the reduced mixing.

Effects of Bulk Flow Pulsations on Film Cooling with Two Sister Holes

“…In their experimental apparatus, five cooling holes were positioned along a row. Here, the computational cost was reduced by applying periodic boundary conditions on the sidewalls [3]. The computational domains are displayed in Figure 1.…”

“…The triple holes consisted of two small holes located downstream of main hole (Figure 2b), as stated by Ely et al [6]. In the triple-hole configuration, D of the primary hole and the sister hole were calculated to match the total cross-sectional areas of the triple holes to the cross-sectional area of the single hole [3]. When the two small holes are located downstream of the main hole, the coolant jets generate an anti-counter-rotating vortex pair (anti-CRVP), and η is increased through the generation of vortices interactions between the injectants and a reduction in the intensity of the main Counter Rotating Vortex Pair [3].…”

“…In the triple-hole configuration, D of the primary hole and the sister hole were calculated to match the total cross-sectional areas of the triple holes to the cross-sectional area of the single hole [3]. When the two small holes are located downstream of the main hole, the coolant jets generate an anti-counter-rotating vortex pair (anti-CRVP), and η is increased through the generation of vortices interactions between the injectants and a reduction in the intensity of the main Counter Rotating Vortex Pair [3]. The hole-length-to-hole-diameter ratio (L/D) for the single-hole system was 1.6, the ratios for the primary hole and each sister hole in the triple hole were 1.8 and 3.6, respectively, the injection angle of the coolant (α) was 35 • .…”

“…However, the turbine blade temperature should remain below the acceptable limit [2]. Film cooling is a widely used in gas turbines [3]. The physics of film cooling under a steady main flow has been widely investigated.…”

“…Using square sister holes, Javadi et al [5] controlled the vortex interactions between injectant and main flow at the blowing ratio, M of 0.5. They numerically found that two sister holes reduced the mixing between the coolant injectant and the crossflow, thereby increasing η. Ely et al [6] numerically investigated the increase in η after forming two sister holes [3]. They varied the blowing ratio among the values 0.2, 0.5, 1.0, and 1.5 and reported an obvious improvement in η at high M. Choi et al [7] numerically investigated performance of the film cooling for double holes by changing design variables such as the lateral ejection angles and streamwise and lateral distances between the holes.…”