Abstract:A trend towards the increasing use of Adaptive Mesh Refinement (AMR) algorithms to simulate combustion processes is seen in the recent literature. AMR is attractive as it enables the physical phenomena of interest to be tracked by the numerical mesh, reducing the computational cost drastically. It is particularly efficient for combustion as small computational cells are needed very locally to resolve the flame structure. However, the questions arising from the coupling between AMR and the turbulent flame propa… Show more
“…However the proposed approach only has an implicit dependence on SGS quantities and filtering is turned off in the region of the flame. Therefore it is well poised to take advantage of the resolution AMR grants without needing additional corrections as is the case when using as efficiency function Mehl et al (2021).…”
Thickened flame models are prolific in the literature and offer an effective method of resolving flame dynamics on coarse LES meshes. The current state of the art relies heavily on the use of efficiency functions to compensate for impaired wrinkling of the thickened flame. However in practice these functions can involve parameters that are difficult to determine, perform poorly outside of certain ranges or require \emph{a posteriori} analysis to evaluate performance.
An alternative based on a generalised thickening is evaluated across a range of canonical configurations. The approach is demonstrated to perform well across a large range of thickening factors in capturing phenomena such as localised quenching and pinch off as well as generation of flame surface. Including good performance even in the case of large flame dynamics under acoustic forcing where the model has a clear advantage over DNS in achieving grid independence.
Finally the approach is unified into an Large Eddy Simulation/Adaptive Mesh Refinement framework and applied to a turbulent Bunsen flame.
The results show that even if the internal flame structure is poorly resolved on the original mesh, the global system behaviour is well predicted and compares favourably with other approaches.
“…However the proposed approach only has an implicit dependence on SGS quantities and filtering is turned off in the region of the flame. Therefore it is well poised to take advantage of the resolution AMR grants without needing additional corrections as is the case when using as efficiency function Mehl et al (2021).…”
Thickened flame models are prolific in the literature and offer an effective method of resolving flame dynamics on coarse LES meshes. The current state of the art relies heavily on the use of efficiency functions to compensate for impaired wrinkling of the thickened flame. However in practice these functions can involve parameters that are difficult to determine, perform poorly outside of certain ranges or require \emph{a posteriori} analysis to evaluate performance.
An alternative based on a generalised thickening is evaluated across a range of canonical configurations. The approach is demonstrated to perform well across a large range of thickening factors in capturing phenomena such as localised quenching and pinch off as well as generation of flame surface. Including good performance even in the case of large flame dynamics under acoustic forcing where the model has a clear advantage over DNS in achieving grid independence.
Finally the approach is unified into an Large Eddy Simulation/Adaptive Mesh Refinement framework and applied to a turbulent Bunsen flame.
The results show that even if the internal flame structure is poorly resolved on the original mesh, the global system behaviour is well predicted and compares favourably with other approaches.
“…The AMR ensures the effectiveness of the computational grid for accuracy and computational time. 38,39 Figure 2.Computational grid on mid-plane (Z = 0) of the referee combustor with adaptive mesh refinement.…”
Section: Computational Methodologymentioning
confidence: 99%
“…The AMR ensures the effectiveness of the computational grid for accuracy and computational time. 38,39 A mesh sensitivity is carried out for swirlers flowsplit study with all passages open to understand solution sensitivity to mesh resolution. The base cell size of 3 mm is fixed and the velocity AMR level is varied as 3, 4, and 5 which yielded minimum cell sizes of 0.375 mm, 0.1875 mm, and 0.09375 mm, respectively, as shown in Table 1.…”
The turbulent flow field in a practical gas turbine combustor is very complex because of the interactions between various flows resulting from components like multiple types of swirlers, dilution holes, and liner effusion cooling holes. Numerical simulations of flows in such complex combustor configurations are challenging. The challenges result from (a) the complexities of the interfaces between multiple three-dimensional shear layers, (b) the need for proper treatment of a large number of tiny effusion holes with multiple angles, and (c) the requirements for fast turnaround times in support of engineering design optimization. Both the Reynolds averaged Navier–Stokes simulation (RANS) and the large eddy simulation (LES) for the practical combustor geometry are considered. An autonomous meshing using the cut-cell Cartesian method and adaptive mesh refinement (AMR) is demonstrated for the first time to simulate the flow in a practical combustor geometry. The numerical studies include a set of computations of flows under a prescribed pressure drop across the passage of interest and another set of computations with all passages open with a specified total flow rate at the plenum inlet and the pressure at the exit. For both sets, the results of the RANS and the LES flow computations agree with each other and with the corresponding measurements. The results from the high-resolution LES simulations are utilized to gain fundamental insights into the complex turbulent flow field by examining the profiles of the velocity, the vorticity, and the turbulent kinetic energy. The dynamics of the turbulent structures are well captured in the results of the LES simulations.
“…In this framework, the target mesh resolution in region of high accuracy remains a parameter defined by the user, for example according to subgrid turbulence, subgrid flame-turbulence interaction criteria or, from a more practical point of view, based on overall computational budget. -Based on systematic, user-independent mesh refinement criteria: AMR has been widely used for the simulation of turbulent propagating flames (Cant et al, 2022;Lapointe et al, 2020;Mehl et al, 2018Mehl et al, , 2021Verhaeghe et al, 2022;Wilkening and Huld, 1999), but most of the methods proposed depend on case-specific thresholds. Indeed, most of the criteria to detect where a fine mesh is required are often based on dimensional quantities: velocity, temperature or species gradients (Cant et al, 2022;Rios et al, 2009), turbulent kinetic energy (Babuska and Miller, 1981), vorticity (Iapichino et al, 2008;Lapointe et al, 2020) or heat release rate (Haldenwang and Pignol, 2002;Lapointe et al, 2020).…”
This paper presents a feature-based Adaptive Mesh Refinement (AMR) method for Large Eddy Simulation of propagating deflagrations, using massive-scale parallel unstructured AMR libraries. The proposed method, named Turbulent Flame Propagation-AMR (TFP-AMR), is able to track the transient dynamics of both the turbulent flame and the vortical structures in the flow. To handle the interaction of the turbulent flame brush with the vortical structures of the flow, a vortex selection criterion is derived from flame/vortex interaction theory. The method is built with the general intent to prioritise conservatively estimated parameters, rather than to rely on user-dependent parameters. In particular, a specific mesh adaptation triggering strategy is constructed, adapted to the strongly transient physics found in deflagrations, to guarantee that the quantities of interest consistently reside within a region of high accuracy throughout the transient process. The methodology is applied and validated on several elementary cases representing fundamental bricks of the full problem: (1) a laminar flame propagation, (2) the advection of a pair of non-reacting vortices, (3) a flame/vortex interaction. The method is then applied to three different configurations of a three-dimensional complex explosion scenario in an obstructed chamber. All cases demonstrate the TFP-AMR capability to recover accurate results at reduced computational cost without requiring any ad hoc tuning of the AMR method or its parameters, thus demonstrating its genericity and robustness.
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