Hybrid RANS-LES Modeling of the Aerothermal Field in an Annular Hot Streak Generator for the Study of Combustor–Turbine Interaction

Abstract

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.

External heat transfer on nozzle guide vanes under highly swirled combustor outlet flow

“…For brevity, only the computational domain and mesh of the NGVs are reported in Fig. 2, however, the grid characteristics and setup of boundary conditions for both simulation cases (NGVs and combined combustor-NGVs) are inherited from Cubeda et al (2018) and Andreini et al (2015Andreini et al ( , 2017.…”

“…Moreover, as Large Eddy Simulation (LES) is still computationally costly, other scale-resolving approaches like Scale-Adaptive Simulation (SAS) (Menter and Egorov, 2004) can reduce the resources effort yet preserving good accuracy. Andreini et al (2017) have compared SAS results with the experiments carried out by Bacci et al (2018a,b) on the EU Project FACTOR ('Full Aerothermal Combustor-Turbine interac-tiOns Research') hot streak generator, which replicates a lean-burn combustor outlet distortion field. The success of SAS in reproducing the coolant/mainstream mixing process more accurately than RANS and, ultimately, the impact on nozzles thermal load and film-cooling adiabatic effectiveness has been lately described by the authors (Cubeda et al, 2018).…”

“…The inlet conditions to the RANS simulation were generated studying the combustor domain (Andreini et al, 2017). In the upper portion of Fig.…”

Uncertainty Quantification of Non-Dimensional Parameters for a Film Cooling Configuration in Supersonic Conditions

“…Numerical simulations are widely used in cooperation with experimental tests, but only recently CFD simulations have been coupled with UQ to study a wide range of turbomachinery problems [13,18,19]. Concerning the present study, a complete description of the experimental facility is reported in [9] and a detailed numerical campaign using the k-ω turbulence model [20] has been reported in [10].…”

“…where the Ma is,c value is calculated using Equation (19). Since both the main-flow and the coolant are modelled using air as perfect gas, they have the same value for γ.…”