Abstract
The effects of bulk flow pulsations on film cooling in gas turbine blades were investigated by conducting large eddy simulation (LES) and Reynolds-averaged Navier–Stokes simulation (RANS). The film cooling flow fields under 32 Hz pulsation in the mainstream from a cylindrical hole inclined 35° to a flat plate at the average blowing ratio of M = 0.5 were numerically simulated. The LES results were compared to the experimental data of Seo, Lee, and Ligrani (1998) and Jung, Lee, and Ligrani (2001). The credibility of the LES results relative to the experimental data was demonstrated through a comparison of the time-averaged adiabatic film cooling effectiveness, time- and phase-averaged temperature contours, Q-criterion contours, time-averaged velocity profiles, and time- and phase-averaged Urms profiles with the corresponding RANS results. The adiabatic film cooling effectiveness predicted using LES agreed well with the experimental data, whereas RANS highly overpredicted the centerline effectiveness. RANS could not properly predict the injectant topology change in the streamwise normal plane, but LES reproduced it properly. In the case of the injectant trajectory, which greatly influences film cooling effectiveness, RANS could not properly predict the changes in the streamwise velocity peak due to flow pulsation, but they were predicted well with LES. RANS greatly underpredicted the streamwise velocity fluctuations, which determine the mixing of main flow and injectant, whereas LES prediction was close to the experimental data.
Highlights
The idealized Brayton cycle indicates that the efficiency of gas turbines could be increased by increasing the turbine inlet temperature [1]
The large eddy simulation (LES) results were compared to the experimental data and the Reynolds-averaged Navier–Stokes simulation (RANS) results to verify the improvement offered by the LES approach relative to the RANS approach in terms of predicting film cooling performance under unsteady flow conditions
The LES results were compared to the experimental data and the results obtained using RANS to determine whether the LES approach better predicted film cooling performance under the unsteady flow condition than the RANS method
Summary
The idealized Brayton cycle indicates that the efficiency of gas turbines could be increased by increasing the turbine inlet temperature [1]. The coolant bled from the compressor is injected onto the blade surface through small holes on the surface, and the resulting coolant film protects the surface from the hot mainstream by reducing the surface temperature. Multiple variables affect the performance of film cooling, and they are often studied by performing numerical analysis to save cost and time. In film cooling flow fields, turbulence is generated, and it can be modeled by conducting Reynolds-averaged Navier–Stokes simulations (RANSs), large eddy simulations (LESs), or by using a hybrid approach such as detached eddy simulation. It is known that the LES approach predicts the mixing between the mainstream and the coolant better than RANS turbulence models, even though its computation time is considerably longer [2,3,4]
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