Large Eddy Simulation of Film Cooling Involving Compound Angle Hole with Bulk Flow Pulsation

Abstract

The effects of pulsations in the main flow on film cooling from a cylindrical hole with a spanwise injection angle (orientation angle) are analyzed using numerical methods. The hole is located on a flat plate with a 35° inclined injection angle, and the compound angle denotes the orientation and inclination angles. The film cooling flow fields for the sinusoidal flow pulsation of 36 Hz from a cylindrical hole with 0° and 30° orientation angles at the time-averaged blowing ratio of M = 0.5 are simulated via large eddy simulation (LES). The CFD results are validated using the experimental data and compared to the Reynolds-averaged Navier–Stokes (RANS) and URANS results. The results reveal that if the pulsation frequency goes from 0 to 36 Hz, the adiabatic film cooling effectiveness decreases regardless of the compound angle; however, the film cooling for the 30° orientation angle exhibits better performance than that for a simple angle (0°). Moreover, if 36 Hz pulsation is applied, the film cooling effectiveness obtained by unsteady RANS exhibits a large deviation from the experimental data, unlike the LES results. The credibility of the LES results relative to the experimental data is demonstrated by comparing the time-averaged η and the phase-averaged temperature contours. The LES results demonstrate that LES can more accurately predict η than the experimental data; in contrast, URANS results are highly overpredicted around the centerline of the coolant spreading. Thus, LES results are more consistent with the experimental results for the time- and phase-averaged temperature contours than the URANS results.

Effects of Bulk Flow Pulsation on Film Cooling Involving Compound Angle

“…More specifically, the time-averaged temperature contours averaged streamwise velocity distribution, and time-averaged turbulence s including urms, vrms, wrms, Reynolds stress such as uv, and uw, and temperature fluct are investigated. The film-cooling effectiveness and temperature contours under pulsations are demonstrated in a previous study [20].…”

“…At steady state, as shown in Figure 8a,b,e,f, the maximum dimensionless temperatures of the coolant core obtained by the RANS are similar to that predicted by the LES or experimental data, whereas with 36-Hz pulsations, the maximum dimensionless temperatures of the coolant core predicted by the URANS are overpredicted because the URANS underpredicted the mixing intensity between the main flow and the injectant during the flow pulsation. In Figure 8b,d,f, the contours for the orientation angle β of 30 • obtained by the experiment in [26], LES, and RANS show that the coolant is inclined and the contact area of the coolant with the wall is increased because the CRVP changes into a single vortex [20], leading to the increase in the film cooling effectiveness on the wall. from the experimental data in [26] at steady state and at M = 1.0.…”

“…flow and the injectant during the flow pulsation. In Figure 8b,d,f, the contours for the orientation angle β of 30° obtained by the experiment in [26], LES, and RANS show that the coolant is inclined and the contact area of the coolant with the wall is increased because the CRVP changes into a single vortex [20], leading to the increase in the film cooling effectiveness on the wall.…”

“…When β was 30 • , the cooling air was injected at a lateral velocity, increasing η by promoting the spanwise spreading of the cooling air on the wall. The counter rotating vortex pair (CRVP) became asymmetric, and the intensity of the vortex pair was weakened [20]. When the intensity of the CRVP decreased, the entrainment of the hot main flow under the injectant was weakened, resulting in a more uniform coolant coverage.…”

Numerical Investigation on Backward-Injection Film Cooling with Upstream Ramps

“…Apparently, the mutual interaction between coolant jets and the mainstream can be controlled by altering either the coolant-jet injection or the oncoming mainstream boundary layer flow. Following this acceptance, many passive strategies (such as compound-angle injection [3][4][5], shaped holes [6][7][8][9], shallow trenches [10][11][12], upstream ramps [13][14][15], etc.) for the film cooling enhancement are developed continuously.…”