LARGE-EDDY SIMULATION OF INTERACTING FILM COOLING JETS

In the present paper the flow field of a film cooling configuration with three staggered rows of holes is investigated using large-eddy simulations (LES). The numerical method uses the MILES approach (monotone-integrated large-eddy simulation) and the discretization of the governing equations is based on a mixed central-upwind AUSM (advective upstream splitting method) scheme with low numerical dissipation. The current investigations focus on full-coverage film cooling with finest drilling holes. The film cooling configuration consists of three staggered rows of holes with a lateral hole spacing of p/D = 3 and a streamwise row distance of l/D = 6. The inclination angle of the cooling holes is alpha = 30 degrees and the flat plate thickness is h/D = 12. The cooling hole exit geometry is fan-shaped with lateral and stream wise expansions. The results evidence the different nature of the mixing process between the jets and the cross:flow after the first, second, and third row. The turbulent kinetic energy peaks at the interaction region of the undisturbed boundary layer with the first row The low velocity ratio leads to reduced velocity gradients in the lower boundary layer downstream of the first row Thus, the turbulence production is reduced at the interaction with the following rows. The adiabatic film cooling effectiveness is substantially improved after the second and third injection and the decay of effectiveness is reduced, respectively. The turbulent heat transfer is investigated and strong variations of the turbulent Prandtl number are evident in the flow field.