LES Study of the Effects of Oscillations in the Main Flow on Film Cooling

The effects of oscillations in the main flow on film cooling in the gas turbine are investigated by Large Eddy Simulation (LES). The film cooling flow fields for the sinusoidal oscillations in the mainstream from a cylindrical hole inclined by 35˚ to a flat plate at the average blowing ratio of M=0.5 are numerically simulated. The LES results are compared to the experimental data from Seo, Lee and Ligrani (1998) and Reynolds-Averaged Navier-Stokes (RANS) results. The experimental results showed that if the oscillation frequencies in the main flow are increased, the adiabatic film cooling effectiveness is decreased. The credibility of the LES results relative to the experimental data is demonstrated by comparison of time-averaged velocity profiles, time-averaged Reynolds stress profiles, phase-averaged temperature contours for the cross–sectional area of coolant, and time-averaged adiabatic film cooling effectiveness. The numerical results indicate that the LES shows a good prediction for the time-averaged velocity profile compared to the experimental data, while RANS doesn’t predict the peak generated by the coolant penetration. It is also observed that LES results for the Reynolds stress show a reasonable agreement to the results of the experiment, whereas RANS results was much smaller compared to the experimental results. The phase-averaged temperature contours for cross–sectional area of coolant obtained by LES are much more consistent with the experimental results than those obtained by RANS. Finally, the adiabatic film cooling effectiveness by LES model show a good match to the experimental results, while RANS results highly over-predict the centerline effectiveness. Paper will discuss these results in detail.