13 research outputs found
Automatic grid refinement criterion for lattice Boltzmann method
In all kinds of engineering problems, and in particular in methods for
computational fluid dynamics based on regular grids, local grid refinement is
of crucial importance. To save on computational expense, many applications
require to resolve a wide range of scales present in a numerical simulation by
locally adding more mesh points. In general, the need for a higher (or a lower)
resolution is not known a priori, and it is therefore difficult to locate areas
for which local grid refinement is required. In this paper, we propose a novel
algorithm for the lattice Boltzmann method, based on physical concepts, to
automatically construct a pattern of local refinement. We apply the idea to the
two-dimensional lid-driven cavity and show that the automatically refined grid
can lead to results of equal quality with less grid points, thus sparing
computational resources and time. The proposed automatic grid refinement
strategy has been implemented in the parallel open-source library Palabos
Three-dimensional central-moments-based lattice Boltzmann method with external forcing: A consistent, concise and universal formulation
The cascaded or central-moments-based lattice Boltzmann method (CM-LBM) is a
robust alternative to the more conventional BGK-LBM for the simulation of
high-Reynolds number flows. Unfortunately, its original formulation makes its
extension to a broader range of physics quite difficult. To tackle this issue,
a recent work [A. De Rosis, Phys. Rev. E 95, 013310 (2017)] proposed a more
generic way to derive concise and efficient three-dimensional CM-LBMs. Knowing
the original model also relies on central moments that are derived in an adhoc
manner, i.e., by mimicking those of the Maxwell-Boltzmann distribution to
ensure their Galilean invariance a posteriori, a very recent effort [A. De
Rosis and K. H. Luo, Phys. Rev. E 99, 013301 (2019)] was proposed to further
generalize their derivation. The latter has shown that one could derive
Galilean invariant CMs in a systematic and a priori manner by taking into
account high-order Hermite polynomials in the derivation of the discrete
equilibrium state. Combining these two approaches, a compact and mathematically
sound formulation of the CM-LBM with external forcing is proposed. More
specifically, the proposed formalism fully takes advantage of the D3Q27
discretization by relying on the corresponding set of 27 Hermite polynomials
(up to the sixth order) for the derivation of both the discrete equilibrium
state and the forcing term. The present methodology is more consistent than
previous approaches, as it properly explains how to derive Galilean invariant
CMs of the forcing term in an a priori manner. Furthermore, while keeping the
numerical properties of the original CM-LBM, the present work leads to a
compact and simple algorithm, representing a universal methodology based on CMs
and external forcing within the lattice Boltzmann framework.Comment: Published in Phys. Fluids as Editor's Pic
Stability of the lattice kinetic scheme and choice of the free relaxation parameter
International audienceThe lattice kinetic scheme (LKS), a modified version of the classical single relaxation time (SRT) lattice Boltzmann (LB) method, was initially developed as a suitable numerical approach for non-Newtonian flow simulations and a way to reduce memory consumption of the original SRT approach. The better performances observed for non-Newtonian flows are mainly due to the additional degree of freedom allowing an independent control over the relaxation of higher-order moments, independently from the fluid viscosity. Although widely applied to fluid flow simulations, yet no theoretical analysis of LKS has been performed. The present work focuses on a systematic von Neumann analysis of the linearized collision operator. Thanks to this analysis, the effect of the modified collision operator on the stability domain and spectral behavior of the scheme are clarified. Results obtained in this study show that correct choices of the "second relaxation coefficient" lead, to a certain extent, to more consistent dispersion and dissipation for large values of the first relaxation coefficient. Furthermore, appropriate values of this parameter can lead to a larger linear stability domain. At moderate and low values of the viscosity, larger values of the free parameter are observed to increase dissipation of kinetic modes, while leaving the acoustic modes untouched and having a less pronounced effect on the convective mode. This increased dissipation leads in general to less pronounced sources of non-linear instability, thus improving the stability of the LKS
Local mesh refinement sensor for the lattice Boltzmann method
A novel mesh refinement sensor is proposed for lattice Boltzmann methods (LBMs) applicable to either static or dynamic mesh refinement algorithms. The sensor exploits the kinetic nature of LBMs by evaluating the departure of distribution functions from their local equilibrium state. This sensor is first compared, in a qualitative manner, to three state-of-the-art sensors: (1) the vorticity norm, (2) the Q-criterion, and (3) spatial derivatives of the vorticity. This comparison shows that our kinetic sensor is the most adequate candidate to propose tailored mesh structures across a wide range of physical phenomena: incompressible, compressible subsonic/supersonic single phase, and weakly compressible multiphase flows. As a more quantitative validation, the sensor is then used to produce the computational mesh for two existing open-source LB solvers based on inhomogeneous, block-structured meshes with static and dynamic refinement algorithms, implemented in the Palabos and AMROC-LBM software, respectively. The sensor is first used to generate a static mesh to simulate the turbulent 3D lid-driven cavity flow using Palabos. AMROC-LBM is then adopted to confirm the ability of our sensor to dynamically adapt the mesh to reach the steady state of the 2D lid-driven cavity flow. Both configurations show that our sensor successfully produces meshes of high quality and allows to save computational time
Bryozoan framework composition in the oddly shaped reefs from Abrolhos Bank, Brazil, southwestern Atlantic: taxonomy and ecology
Ramalho, Laís V., Taylor, Paul D., Moraes, Fernando Coreixas, Moura, Rodrigo, Amado-Filho, Gilberto M., Bastos, Alex C. (2018): Bryozoan framework composition in the oddly shaped reefs from Abrolhos Bank, Brazil, southwestern Atlantic: taxonomy and ecology. Zootaxa 4483 (1): 155-186, DOI: https://doi.org/10.11646/zootaxa.4483.1.