The adoption of lean-burn technology in modern aero-engines influences the already critical aerothermal conditions at turbine entry, where the absence of dilution holes preserves the swirl component generated by burners and prevents any control on pattern factor. The associated uncertainty and lack of confidence entail the application of wide safety margins in turbine cooling design, with a detrimental effect on engine efficiency. Computational fluid dynamics (CFD) can provide a deeper understanding of the physical phenomena involved in combustor–turbine interaction, especially with hybrid Reynolds-averaged Navier–Stokes (RANS) large eddy simulation (LES) models, such as scale adaptive simulation (SAS), which are proving to overcome the well-known limitations of the RANS approach and be a viable approach to capture the complex flow physics. This paper describes the numerical investigation on a test rig representative of a lean-burn, effusion cooled, annular combustor developed in the EU Project Full Aerothermal Combustor-Turbine interactiOns Research (FACTOR) with the aim of studying combustor–turbine interaction. Results obtained with RANS and SAS were critically compared to experimental data and analyzed to better understand the flow physics, as well as to assess the improvements related to the use of hybrid RANS-LES models. Significant discrepancies are highlighted for RANS in predicting the recirculating region, which has slight influence on the velocity field at the combustor outlet, but affects dramatically mixing and the resulting temperature distribution. The accuracy of the results achieved suggests the exploitation of SAS model with a view to the future inclusion of the nozzle guide vanes in the test rig.

Effusion cooling represents the state-of-the-art of liner cooling technology for modern combustors. The present paper describes experimental tests aiming at evaluating the cooling performance of a multi-perforated plate in real engine representative fluid- dynamic conditions. Adiabatic effectiveness maps were obtained following the mass transfer analogy by the use of Pressure Sensitive Paint. In addition, a CFD campaign was performed in order to benchmark the reliability in estimating the cooling performance of effusion cooling liners. In order to include anisotropic diffusion effects, the k − ω SST turbulence model was corrected considering a tensorial definition of the eddy viscosity with an algebraic correction to dope its stream-span components

State-of-the-art liner cooling technology for modern combustion chambers is represented by effusion cooling (or full-coverage film cooling). Effusion is a very efficient cooling strategy typically based on the use of several inclined small diameter cylindrical holes, where liner temperature is controlled by the combined protective effect of coolant film and heat removal through forced convection inside each hole. A CFD-based thermal analysis of such components implies a significant computational cost if the cooling holes are included in the simulations; therefore many efforts have been made to develop lower order approaches aiming at reducing the number of mesh elements. The simplest approach models the set of holes as a uniform coolant injection, but it does not allow an accurate assessment of the interaction between hot gas and coolant. Therefore higher order models have been developed, such as those based on localized mass sources in the region of hole discharge. The model presented in this paper replaces the effusion hole with a mass sink on the cold side of the plate, a mass source on the hot side, whereas convective cooling within the perforation is accounted for with a heat sink. The innovative aspect of the work is represented by the automatic calculation of the mass flow through each hole, obtained by a run time estimation of isentropic mass flow with probe points, while the discharge coefficients are calculated at run time through an in-house developed correlation. In the same manner, the heat sink is calculated from a Nusselt number correlation available in literature for short length holes. The methodology has been applied to experimental test cases of effusion cooling plates and compared to numerical results obtained through a CFD analysis including the cooling holes, showing a good agreement. A comparison between numerical results and experimental data was performed on an actual combustor as well, in order to prove the feasibility of the procedure.