Analysis of subgrid scale models

Abbà, Antonella; Cercignani, A.C.; Valdettaro, Lorenzo

doi:10.1016/s0898-1221(03)90014-9

Cited by 35 publications

(48 citation statements)

References 16 publications

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“…The variability in space and time of the coefficient C in Equation can induce numerical instabilities. Therefore, it is customary to average over homogeneous direction and/or in time and to clip negative peaks of the subgrid scale viscosity. As for the averaging procedure, we notice that we cannot perform it, as it is commonly done in situations with statistically spatial homogeneity directions or temporal stationarity, due to the very different physical regimes that are present in our system both in space and time.…”

Section: Numerical Resultsmentioning

confidence: 99%

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Large eddy simulations for blood dynamics in realistic stenotic carotids

Lancellotti

Vergara

Valdettaro

et al. 2017

Numer Methods Biomed Eng

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In this paper, we consider large eddy simulations (LES) for human stenotic carotids in presence of atheromasic plaque, a pathological condition where transitional effects to turbulence may occur, with relevant clinical implications such as plaque rupture. We provide a reference numerical solution obtained at high resolution without any subgrid scale model, to be used to assess the accuracy of LES simulations. In the context we are considering, ie, hemodynamics, we cannot refer to a statistically homogeneous, isotropic, and stationary turbulent regime; hence, the classical Kolmogorov theory cannot be used. For this reason, a mesh size and a time step are deemed fine enough if they allow to capture all the features of the velocity field in the shear layers developed after the bifurcation. To assess these requirements, we consider a simplified model of the evolution of a 2D shear layer, a relevant process in the formation of transitional effects in our case. Then, we compare the results of LES σ model (both static and dynamic) and mixed LES models (where also a similarity contribution is considered). In particular, we consider a realistic scenario of a human carotid, and we use the reference solution as gold standard. The results highlight the accuracy of the LES σ models, especially for the static model.

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Section: Numerical Resultsmentioning

confidence: 99%

“…The next steps will be the applications to different arterial districts (such as the aorta), the inclusion of fluid‐structure interaction to account for the vessel displacements and the test of turbulence models that take into account anisotropy effects …”

Section: Discussionmentioning

confidence: 99%

Large eddy simulations for blood dynamics in realistic stenotic carotids

Lancellotti

Vergara

Valdettaro

et al. 2017

Numer Methods Biomed Eng

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“…The resolved scales are obtained by introducing a spatial filter function, which removes the unresolvable small scales of turbulence. Of course, for the same physical conditions, the numerical cost of LES is expected to be much lower than that of direct numerical simulation [16].…”

Section: Governing Equations and Numerical Methodologymentioning

confidence: 99%

Investigation of density ratio effects on normally injected cold jets into a hot cross flow

2007

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In this work, hydrodynamic effects of multiple squared cross-section cold jets inclined normally into a hot cross flow were computationally simulated using large eddy simulation (LES) approach. The finite volume method and the SIMPLE algorithm on a multi-block non-uniform staggered grid were applied. The jet into cross flow velocity ratio and the jet Reynolds number were 0.5 and 4,700, respectively. Simulations were performed for three different jets into cross flow temperature ratios, namely, 2, 1, and 0.5, corresponding to density ratios of 0.5, 1, and 2. The experimental and numerical results of Ajersch et al. (J. Turbomachinery 119(2), [330][331][332][333][334][335][336][337][338][339][340][341][342] 1997) at unit density ratio were used for validation purposes. The density ratio effects on the flow characteristics were investigated. It was shown that the density ratio has significant effects on the hydrodynamics of the jet into cross flow problems and even though the flow Mach number may be low, its effects due to temperature differences between the jet and the cross flow cannot be easily ignored.

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“…2,3 Due to the stochastic nature of SGS stresses, the consistent diagnostics of deterministic SGS models from a priori and a posteriori tests has been quite difficult. In addition, it has been reported [8][9][10] that high correlation coefficients observed in a priori tests of the scale similarity model, 6,11 mixed-type models, 6,12,13 and recently developed deconvolution based models 14,15 mostly come from deterministic correlations between the resolved subfilter scale stresses 16 and their approximations when formally invertible filters are adopted. On the other hand, in a posteriori tests, an actual LES with a SGS model is performed and statistics are compared with those from (filtered) DNS or experiment.…”

Section: Introductionmentioning

confidence: 99%

Toward improved consistency of a priori tests with a posteriori tests in large eddy simulation

2004

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It is well known that conventional a priori tests based on the instantaneous true subgrid scale (SGS) stress do not provide a useful diagnostic information on deterministic SGS models due to the stochastic nature of unresolved scales. In this study, the possibility of an alternative diagnostics based on the "best deterministic" model is investigated. The optimal SGS model [J. A. Langford and R. D. Moser, "Optimal LES formulation for isotropic turbulence," J. Fluid Mech. 398, 321 (1999)] is considered as one of nearly best deterministic models. The validity of the optimal model is confirmed by a posteriori test, showing that the field from the optimal large eddy simulation can be regarded as one of the representative fields among all the possible realizations of filtered direct numerical simulation. Then, a priori and a posteriori tests for several SGS models are performed on the forced isotropic turbulence with a sharp cutoff filter. It is shown that a priori tests based on the optimal model are highly consistent with a posteriori tests. Also, dynamic eddy viscosity models are very close to the optimal model both in a priori and a posteriori senses, which implies that the accurate prediction of backward dissipation is not necessarily required for the deterministic model to predict accurate flow statistics at least for the isotropic turbulence. Therefore, the direct application of scale-invariance concept to the resolved field is shown to be unsuccessful for the spectral cutoff filter. The present study strongly suggests that this concept should be realized in terms of the dynamic constant(s) of dissipative models.

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Analysis of subgrid scale models

Cited by 35 publications

References 16 publications

Large eddy simulations for blood dynamics in realistic stenotic carotids

Large eddy simulations for blood dynamics in realistic stenotic carotids

Investigation of density ratio effects on normally injected cold jets into a hot cross flow

Toward improved consistency of a priori tests with a posteriori tests in large eddy simulation

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