Large-eddy Simulation of Film Cooling Flows with Variable Density Jets

Abstract

The present paper investigates the impact of the velocity and density ratio on the turbulent mixing process in gas turbine blade film cooling. A cooling fluid is injected from an inclined pipe at α=30 • into a turbulent boundary layer profile at a freestream Reynolds number of Re ∞ = 400,000. This jet-in-a-crossflow (JICF) problem is investigated using large-eddy simulations (LES). The governing equations comprise the Navier-Stokes equations plus additional transport equations for several species to simulate a non-reacting gas mixture. A variation of the density ratio is simulated by the heat-mass transfer analogy, i.e., gases of different density are effused into an air crossflow at a constant temperature. An efficient largeeddy simulation method for low subsonic flows based on an implicit dual timestepping scheme combined with low Mach number preconditioning is applied. The numerical results and experimental velocity data measured using two-component particle-image velocimetry (PIV) are in excellent agreement. The results show the dynamics of the flow field in the vicinity of the jet hole, i.e., the recirculation region and the inclination of the shear layers, to be mainly determined by the velocity ratio. However, evaluating the cooling efficiency downstream of the jet hole the mass flux ratio proves to be the dominant similarity parameter, i.e., the density ratio between the fluids and the velocity ratio have to be considered.

Numerical Study on Flat Plate and Leading Edge Film Cooling

“…This might come from the difference of vortex structure after the cooling hole exit, that should be strongly influenced by the turbulence level around the cooling hole. [19] x/d ) 0.5 /U m . Since turbulence was not imposed at the inlet of the main stream region in the DES simulation, the distribution of TL is much different from the one measured by Pietrzyk et al [24].…”

“…10. The results of previous experiments [15][16][17] and LES simulations [3,9,19] are also plotted in the figure. The LES results agree well with the experiments.…”

“…Film cooling flow fields around a circular hole on a flat plate were analyzed by the RANS simulation with k-ω type turbulence models, they are shearstress transport (SST) model [10], k-ω model with the modification of Kato-Launder [11] and k-ω with time-scale bound [12], as well as the DES [13] based on Spalart-Allmaras (S-A) model [14]. The results were compared with each other and with the previous experimental and numerical results [3,9,[15][16][17][18][19]. In preparation for the simulations of film cooling flow on semi-cylindrical leading edge, the effect of plenum flow on film cooling effectiveness was also investigated by the RANS simulation.…”

Dominant Vortex Structures in Transverse Jets

“…Fuller and Walters (1991), Williams and Hartfield (1996) and Wang (2000) used different inclination angle such as 25, 35, 45 and 60 revealing the velocity and vorticity fields. Most of reported studies on inclined jets dealt with the effects of inclination angle on the flow structure associated with film cooling phenomena such as Rowbury et al (2001), Bayraktar and Yilmaz (2008), Renze et al (2008) and Bayraktar and Yilmaz (2011).…”

A numerical study of rotation effects on jets effusing from inclined holes into a cross-flow

“…The results showed that the higher values of VR have a strong impact on Downloaded by [New York University] at 22:46 23 June 2015 the cooling performance because it causes a stronger penetration of the jet in cross-flow, resulting in large streamwise vortices downstream of the jet exit and entrains the cross-flow partially into this zone. Later, the impact of density and VRs was investigated by Renze et al [12] using LES. Gases of different densities were injected from an inclined pipe at 30 • into an airstream at a freestream Reynolds number of 400,000 and different values of VR of 0.1, 0.28, and 0.48.…”