A grid-independent length scale for large-eddy simulations

Piomelli, Ugo; Rouhi, Amirreza; Geurts, Bernardus J.

doi:10.1017/jfm.2015.29

Cited by 66 publications

(53 citation statements)

References 59 publications

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“…However, it is more convenient to use the length-scale ratio R S = L z /l S in LES. For example, Piomelli et al (2015) recently developed a grid-independent LES using as parameter the ratio of the small (effective Kolmogorov) and integral scales, which is essentially the inverse of R S . It can be extended to DNS by substituting η for l S (L z /η ∼ Re 3/4 z ) and it turns out that, in DNS of SS-HST, Re z ≈ 4R 4/3 S ).…”

Section: Large-eddy Simulations With Sinuous Symmetrymentioning

confidence: 99%

Vertically localised equilibrium solutions in large-eddy simulations of homogeneous shear flow

Sekimoto

Jiménez

2017

J. Fluid Mech.

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Unstable equilibrium solutions in a homogeneous shear flow with sinuous (streamwiseshift-reflection and spanwise-shift-rotation) symmetry are numerically found in largeeddy simulations (LESes) with no kinetic viscosity. The small-scale properties are determined by the mixing length scale l S used to define eddy viscosity, and the large-scale motion is induced by the mean shear at the integral scale, which is limited by the spanwise box dimension L z . The fraction R S = L z /l S , which plays the role of a Reynolds number, is used as a numerical continuation parameter. It is shown that equilibrium solutions appear by a saddle-node bifurcation as R S increases, and that the flow structures resemble those in plane Couette flow with the same sinuous symmetry. The vortical structures of both lower-and upper-branch solutions become spontaneously localised in the vertical direction. The lower-branch solution is an edge state at low R S , and takes the form of a thin critical layer as R S increases, as in the asymptotic theory of generic shear flow at high-Reynolds numbers. On the other hand, the upper-branch solutions are characterised by a tall velocity streak with multi-scale multiple vortical structures. At the higher end of R S , an incipient multiscale structure is found. The LES turbulence occasionally visits vertically localised states whose vortical structure resembles the present vertically localised LES equilibria.

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Section: Large-eddy Simulations With Sinuous Symmetrymentioning

confidence: 99%

Vertically localised equilibrium solutions in large-eddy simulations of homogeneous shear flow

Sekimoto

Jiménez

2017

J. Fluid Mech.

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“…These discontinuities may cause numerical instabilities and do not always reflect the flow physics; a refined treatment would require explicit accounting of commutator errors associated with strongly varying filter widths [6]. Piomelli et al [7] discuss these issues in depth.…”

Section: Introductionmentioning

confidence: 99%

“…An alternative definition of decouples the filter width from the grid [7]. In this paper, the authors propose a model length scale that is instead related to the turbulence itself, by calculating an approximation of the local integral length scale L est and setting ∝ L est [integral length-scale approximation (ILSA)].…”

Section: Introductionmentioning

confidence: 99%

“…In this way, the LES is turned into a physical model for turbulence and full independent control is possible over numerical errors. Piomelli et al [7] estimated L est based on the resolved turbulent kinetic energy and total dissipation; the single model constant C k was determined by requiring that the SFSs contribute a given amount to the total dissipation [8]. Decreasing C k is equivalent to decreasing the filter width and hence enhancing the physical resolution.…”

Section: Introductionmentioning

confidence: 99%

“…[7] C k is a global constant, calculated once, before the production simulation is performed. A target value for the chosen measure of SFS activity [8], s ε (the ratio of the SFS dissipation to the total, viscous and SFS, one), was assigned and the corresponding C k was obtained by performing several coarse-grid calculations, using the successive inverse polynomial interpolation approach for computational error reduction [11].…”

Section: Introductionmentioning

confidence: 99%

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Dynamic subfilter-scale stress model for large-eddy simulations

2016

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We present a modification of the integral length-scale approximation (ILSA) model originally proposed by Piomelli et al. [Piomelli et al., J. Fluid Mech. 766, 499 (2015)] and apply it to plane channel flow and a backward-facing step. In the ILSA models the length scale is expressed in terms of the integral length scale of turbulence and is determined by the flow characteristics, decoupled from the simulation grid. In the original formulation the model coefficient was constant, determined by requiring a desired global contribution of the unresolved subfilter scales (SFSs) to the dissipation rate, known as SFS activity; its value was found by a set of coarse-grid calculations. Here we develop two modifications. We define a measure of SFS activity (based on turbulent stresses), which adds to the robustness of the model, particularly at high Reynolds numbers, and removes the need for the prior coarse-grid calculations: The model coefficient can be computed dynamically and adapt to large-scale unsteadiness. Furthermore, the desired level of SFS activity is now enforced locally (and not integrated over the entire volume, as in the original model), providing better control over model activity and also improving the near-wall behavior of the model. Application of the local ILSA to channel flow and a backward-facing step and comparison with the original ILSA and with the dynamic model of Germano et al. [Germano et al., Phys. Fluids A 3, 1760(1991 show better control over the model contribution in the local ILSA, while the positive properties of the original formulation (including its higher accuracy compared to the dynamic model on coarse grids) are maintained. The backward-facing step also highlights the advantage of the decoupling of the model length scale from the mesh.

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