Design of implicit high-order filters on unstructured grids for the identification of large-scale features in large-eddy simulation and application to a swirl burner

Guedot, Lola; Lartigue, Ghislain; Moureau, Vincent

doi:10.1063/1.4917280

Cited by 23 publications

(34 citation statements)

References 40 publications

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“…Visualization of Qcriterion with LES simulation is more prone to show smaller structures, making the visualization of relevant topologies very difficult. Therefore, high order filtering based on the mesh size has been used to filter the smaller vortices and to visualize only the big scales of the structure [11]. As LES needs a lot of computational resources, a limited number of operating points have been studied.…”

Section: Comparison Of the Vortex Topologies Between Rans Simulationsmentioning

confidence: 99%

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Doussot¹,

Balarac²,

Brammer³

et al. 2020

IJFMS

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Hydraulic machines are designed to operate in flow conditions close to the best efficiency point. However, to respond to the increasing demand for flexibility mainly due to the integration of renewable energy in the electric grid, the operating range of Francis turbines has to be extended towards smaller discharge levels without restriction. When Francis turbines are operated typically between 30% and 60% of the rated output power, the flow field is characterized by the appearance of inter-blade vortices in the runner. In these off-design operating conditions and due to these phenomena, dynamic stresses level can increase, and potentially lead to fatigue damage of the mechanical structure of the machine. The objective of this paper is to present investigations on the dynamic behaviour of the inter-blade vortices and their impact on the runner by using numerical simulations. Computations were performed with different turbulence modelling approaches to assess their relevance and reliability: Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES). Computations aimed to better understand the emergence condition of the inter-blade vortices. The analysis showed that vortices can be generated due to poor inlet adaptation at part load, however other vortices can also be due to a local backflow in the runner. The competition between these both phenomena leads to various topologies of the inter-blade vortices. The numerical results were compared to experimental visualizations performed on scaled model as well as to previous numerical studies results. The impact of these inter-blade vortices on the runner were also investigated by considering the pressure fluctuations induced on the blades. The dynamic loading on the blade has to be known in order to evaluate the lifetime of the runner by mechanical analysis. Different operating conditions have been simulated to understand how the pressure fluctuations depend on the operating conditions. The localization of the pressure fluctuations and their consequences on the frequency signature of the torque fluctuations have been analyzed. This article is presenting a part of the work presented at the 29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, 2018 [1], and presents another vortex topology and a comparison of LES results of several operating conditions.

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Section: Comparison Of the Vortex Topologies Between Rans Simulationsmentioning

confidence: 99%

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Doussot¹,

Balarac²,

Brammer³

et al. 2020

IJFMS

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“…This code solves the low-Mach number NavierStokes equations for turbulent reactive flows on unstructured meshes using a projection method for constant [37] or variable density flows [38]. It relies on fourth-order central finite-volume schemes and on highly efficient linear solvers [39], which enable the simulation and the post-processing of isothermal or reacting flows on massive unstructured grids [40,41].…”

Section: Application In Canonical Test Casesmentioning

confidence: 99%

Mesh adaptation for large‐eddy simulations in complex geometries

Bénard

Balarac

Moureau

et al. 2015

Numerical Methods in Fluids

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International audienceLarge-eddy simulation (LES) consists in explicitly simulating the large scales of the fluid motion and in modeling the influence of the smallest scales. Thanks to the steady growth of computational resources, LES can now be used to simulate realistic systems with complex geometries. However, when LES is used in such complex geometries, an adequate mesh has to be determined to perform valid LES. In this work, a strategy is proposed to assess the quality of a given mesh and to adapt it locally. Two different criteria are used as mesh adaptation criteria. The first criterion is defined to ensure a correct discretization of the mean field, whereas the second criterion is defined to ensure enough explicit resolution of turbulent scales motions. The use of both criteria is shown in canonical flow cases. As a second part of this work, a numerical strategy for mesh adaptation in high-performance computing context is proposed by coupling the flow solver, YALES2, and the remeshing library, MMG3D, for massively parallel computations. This coupling enables an efficient and parallel remeshing of grids alleviating any memory or performance issues encountered in sequential tools. This strategy is finally applied to the simulation of the isothermal flow in a complex meso-combustor to demonstrate the applicability of the adaptation methodology to complex turbulent flows

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“…YALES2 solver is able to deal with unstructured grids composed only by tetrahedron elements or by prisms and tetrahedron elements, allowing to perform LES or DNS of complex geometries in the context of massively parallel computations. The solver has been validated for various applications such as combustion [41,42], biomechanics [43], hydro-electricity [44], wind energy [45], or multiphase flows [46]. In this work, the equations are solved in a rotating frame and a rotating velocity condition is imposed at the inlet.…”

Section: Numerical Set-upmentioning

confidence: 99%

Large Eddy Simulations on Vertical Axis Hydrokinetic Turbines - Power coefficient analysis for various solidities

et al. 2020

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Large Eddy Simulations (LES) are performed on a Vertical Axis Hydrokinetic Turbine (VAHT) at two different solidities, so as to enable a more complete physical description of the flow than for classic statistical calculations. To analyze the turbine performances, local quantities are defined to evaluate the contribution of the different turbine elements to the global VAHT power coefficient. For a deeper analysis of the major losses, the real turbine is also compared with an ideal turbine composed of only three infinite blades. It is observed that the ideal turbine with the lower solidity provides the best performance, but the losses due to the blade tips and the arms strongly increase for the real turbine at the same solidity. Consequently, for the considered real turbine, there is no clear gain to decrease the solidity. Simulations of the ideal turbine are performed for various solidities at their optimal Tip Speed Ratio (TSR) to study the evolution of optimal power coefficient as a function of solidity. A maximum power coefficient is obtained for a small value of the solidity. This is explained because the optimal TSR of this optimal solidity leads to angles of incidences on the blade which avoid a penalizing dynamic stall phenomenon but are high enough to produce an important positive torque The design of an efficient turbine has then to limit losses, to be able to use small solidity and then to avoid dynamic stall phenomenon by having a high optimal TSR.

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Design of implicit high-order filters on unstructured grids for the identification of large-scale features in large-eddy simulation and application to a swirl burner

Cited by 23 publications

References 40 publications

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Mesh adaptation for large‐eddy simulations in complex geometries

Large Eddy Simulations on Vertical Axis Hydrokinetic Turbines - Power coefficient analysis for various solidities

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