• Energy Research

Abstract Swirl burners are widely used in aeronautical engines and industrial gas turbines. These burners enhance the flame stabilization by bringing back hot products to the reactive zone and their topology ensures a good compactness. However, the outer recirculation zones created in these burners induce wall heat loss that affects the flame structure. This paper proposes a numerical strategy based on Large-Eddy Simulation (LES) and non-adiabatic boundary conditions with a skeletal chemistry approach coupled to the Dynamic Thickened Flame model (TFLES). Simulations were performed on the PRECCINSTA burner with meshes up to 877 millions elements. Results demonstrated the impact of the addition of wall heat loss on the lift-off of the external flame front, leading to a flame topology change from a M-shape to a V-shape. This lift-off height increases with the grid resolution showing the strong influence of the mesh resolution on the flame topology. Comparisons of the non-adiabatic LES results on the finest mesh with the experimental data show an unprecedented agreement. The flame quenching process is analyzed and exhibits the role of strain rate which controls the level of penetration of cooled products within the inner reaction zone.

Accurate simulation of wind turbine wakes is critical for the optimization of turbine efficiency and prediction of fatigue loads. These wakes are three-dimensional, complex, unsteady and can evolve in geometrically complex environments. Modeling these flows calls thus for high-quality numerical methods that are able to capture and transport thin vortical structures on an unstructured grid. It is proposed here to assess the performances of a fourth-order finite-volume LES solver to perform massively parallel scale-resolving simulations of wind turbines wakes. In this framework, the actuator line method that takes the effect of the wind turbine blades on the flow into account is implemented. It is demonstrated that both near and far parts of the turbine wakes are accurately modeled as well as geometrical details. The methodology is assessed on two different test cases and validated with experimental results. It is demonstrated that the flow predictions are of equivalent quality on both structured and unstructured grids. The influence of the geometrical details (e.g. nacelle and tower) on the wake development as well as the influence of the discretization scheme are also investigated.

Abstract A quasi–cubic meso-scale air/methane whirl flow combustion chamber, with no moving parts, is analyzed by means of high-fidelity Large-Eddy Simulations (LES). In order to consider partially premixed flames and differential diffusion process into the combustor, 3D LES computations include semi-detailed chemical kinetics mechanism and complex transport. They show that the reacting flow structure, flame topology and global efficiency are in line with previous experimental and less detailed numerical modeling. Combustion is stabilized by a Central Recirculation Zone (CRZ) and mainly takes place in premixed lean regime. Wall heat losses are also estimated and incomplete combustion zones are identified. Performances improvement was tested with hydrogen addition to fuel mixture. A small amount of hydrogen shows a global efficiency rise while keeping the whirl flow topology. The addition of a large amount of hydrogen implies a change in flame topology leading to a less complete combustion and pollutant formation. These results are in agreement with experimental data.