Numerical investigation of optimized arrangements for effusion cooling in gas turbine combustor applications

The high cooling performance and the capability of providing thermo-acoustic damping are increasing the application of effusion cooling in lean burn aero-engine combustors. The numerical characterization through Computational Fluid Dynamics (CFD) has gained strong interest, however standard Reynolds Average Navier-Stokes (RANS) techniques are not capable of providing high fidelity predictions in the presence of swirling flows interacting with the cooling system. The exploitation of Large Eddy Simulation (LES) would represent the ideal solution, but the high spatial resolution required in the near-wall region, together with the well-known issues related to an accurate specification of turbulent boundary conditions at the inlets, still represent a critical challenge for its extensive use with realistic conditions in terms of Reynolds number and geometrical complexity. Therefore different scale-resolving models such as Scale Adaptive Simulation (SAS) and Detached Eddy Simulation (DES) are gaining popularity due to the promising results highlighted. At this purpose, a SAS approach was employed in this work to quantify the film coverage offered by different effusion cooling schemes in the presence of a swirler, highly unsteady flow field. The main goal is determine if well-known design practices derived from investigations carried out on flat plates with uniform mainstream conditions may be confirmed also under realistic flow conditions. In particular, the geometrical parameters evaluated in the work are the inclination angle, the compound angle and the pattern of the perforation. The results clearly highlight how a reduction of the inclination angle is able to keep coolant more attached to the wall, whereas the application of a compound angle increases the turbulent diffusion in the lateral direction, ultimately increasing coolant protection.