Large Eddy Simulation of Film Cooling Involving Compound Angle Holes: Comparative Study of LES and RANS

Abstract

A large eddy simulation (LES) was performed for film cooling in the gas turbine blade involving spanwise injection angles (orientation angles). For a streamwise coolant injection angle (inclination angle) of 35°, the effects of the orientation angle were compared considering a simple angle of 0° and 30°. Two ratios of the coolant to main flow mass flux (blowing ratio) of 0.5 and 1.0 were considered and the experimental conditions of Jung and Lee (2000) were adopted for the geometry and flow conditions. Moreover, a Reynolds averaged Navier–Stokes simulation (RANS) was performed to understand the characteristics of the turbulence models compared to those in the LES and experiments. In the RANS, three turbulence models were compared, namely, the realizable k-ε, k-ω shear stress transport, and Reynolds stress models. The temperature field and flow fields predicted through the RANS were similar to those obtained through the experiment and LES. Nevertheless, at a simple angle, the point at which the counter-rotating vortex pair (CRVP) collided on the wall and rose was different from that in the experiment and LES. Under the compound angle, the point at which the CRVP changed to a single vortex was different from that in the LES. The adiabatic film cooling effectiveness could not be accurately determined through the RANS but was well reflected by the LES, even under the compound angle. The reattachment of the injectant at a blowing ratio of 1.0 was better predicted by the RANS at the compound angle than at the simple angle. The temperature fluctuation was predicted to decrease slightly when the injectant was supplied at a compound angle.

Effects of Bulk Flow Pulsation on Film Cooling Involving Compound Angle

“…In the RANS contour, the thickness of the coolant in the region between 0.5 ≤ |z/D| ≤ 1.5 is less than that of the LES results because the RANS predicts a weaker interaction of the coolant with the coolant in the virtual neighboring rows obtained by the periodic boundary conditions on the main sides For all cases with the orientation angle β of 0 • , both the LES and RANS results show that the largest and smallest boundary layer thickness occurred at z/D = 0 and approximately z/D = 0.5, respectively. Therefore, the maximum heat transfer coefficient is expected to occur at approximately z/D = 0.5 and the minimum heat transfer coefficient is expected to occur at z/D = 0 [33].…”

“…In Figure 11c, if the pulsation of 36 Hz is applied to the flow, the values of the Reynolds stress are increased drastically around the core of the coolant and the peaks of the Reynolds stress in the shear layer over the coolant core appear. When the orientation angle (β) of 30 • is adopted, the cooling air is injected at a lateral velocity and the Reynolds stress is generated around the single vortex [33].…”

“…In Figure 11c, if the pulsation of 36 Hz is applied to the flow, the values of the Reynolds stress are increased drastically around the core of the coolant and the peaks of the Reynolds stress in the shear layer over the coolant core appear. When the orientation angle (β) of 30° is adopted, the cooling air is injected at a lateral velocity and the Reynolds stress is generated around the single vortex [33]. Figure 12 shows the contours of the urms and vrms of the turbulence intensity and the Reynolds stress uv for the plane at z = 0 obtained by the LES at steady state and with flow pulsations of 36 Hz at M = 0.5 and 1.0 for the orientation angle β of 0° in comparison with the experimental data from a study by Coletti et al [35] at M = 1.0.…”

Research of Flow Stability of Non-Newtonian Magnetorheological Fluid Flow in the Gap between Two Cylinders

“…A less demanding variant with respect to the grid requirements in comparison with DNS is the LES approach [21]. From the point of view of applications, it is effective to monitor the first stable vortex structures in the flow between two concentric cylinders.…”