Hybrid Lattice-Boltzmann-Potential Flow Simulations of Turbulent Flow around Submerged Structures

We report on the development and validation of a 3D hybrid Lattice Boltzmann Model (LBM), with Large Eddy Simulation (LES), to simulate the interactions of incompressible turbulent flows with ocean structures. The LBM is based on a perturbation method, in which the velocity and pressure are expressed as the sum of an inviscid flow and a viscous perturbation. The far- to near-field flow is assumed to be inviscid and represented by potential flow theory, which can be efficiently modeled with a Boundary Element Method (BEM). The near-field perturbation flow around structures is modeled by the Navier–Stokes (NS) equations, based on a Lattice Boltzmann Method (LBM) with a Large Eddy Simulation (LES) of the turbulence. In the paper, we present the hybrid model formulation, in which a modified LBM collision operator is introduced to simulate the viscous perturbation flow, resulting in a novel perturbation LBM (pLBM) approach. The pLBM is then extended for the simulation of turbulence using the LES and a wall model to represent the viscous/turbulent sub-layer near solid boundaries. The hybrid model is first validated by simulating turbulent flows over a flat plate, for moderate to large Reynolds number values, Re ∈ [3.7×104;1.2×106]; the plate friction coefficient and near-field turbulence properties computed with the model are found to agree well with both experiments and direct NS simulations. We then simulate the flow past a NACA-0012 foil using a regular LBM-LES and the new hybrid pLBM-LES models with the wall model, for Re = 1.44 x 106. A good agreement is found for the computed lift and drag forces, and pressure distribution on the foil, with experiments and results of other numerical methods. Results obtained with the pLBM model are either nearly identical or slightly improved, relative to those of the standard LBM, but are obtained in a significantly smaller computational domain and hence at a much reduced computational cost, thus demonstrating the benefits of the new hybrid approach

Near-wall modeling of forests for atmosphere boundary layers using lattice Boltzmann method on GPU

In this paper, the simulation and modeling of the turbulent atmospheric boundary layers (ABLs) in the presence of forests are studied using a lattice Boltzmann method with large eddy simulation, which was implemented in the open-source program GASCANS with the use of Graphic Processing Units (GPU). A method of modeling forests in the form of body forces injected near the wall is revisited, while the effects of leaf area density (LAD) on the model accuracy is further addressed. Since a uniform cell size is applied throughout the computational domain, the wall-normal height of the near-wall cells is very large, theoretically requiring a wall function to model the boundary layer. However, the wall function is disregarded here when the forest is modeled. This approximation is validated based on the comparison with previous experimental and numerical data. It concludes that for the ABL conditions specified in this study as well as a large body of literature, the forest forces overwhelm the wall friction so that the modeling of the latter effect is trivial. Constant and varying LAD profiles across the forest zone are defined with the same total leaf area despite the varying one being studied previously. It is found that the two LAD profiles provide consistent predictions. The present forest modeling can therefore be simplified with the use of the constant LAD without degrading the model accuracy remarkably

Law of the wall in an unstably stratified turbulent channel flow

We perform direct numerical simulations of an unstably stratified turbulent channel flow to address the effects of buoyancy on the boundary layer dynamics and mean field quantities. We systematically span a range of parameters in the space of friction Reynolds number ($Re_{\tau}$) and Rayleigh number ($Ra$). Our focus is on deviations from the logarithmic law of the wall due to buoyant motion. The effects of convection in the relevant ranges are discussed providing measurements of mean profiles of velocity, temperature and Reynolds stresses as well as of the friction coefficient. A phenomenological model is proposed and shown to capture the observed deviations of the velocity profile in the log-law region from the non-convective case

Real Time Wake Computations using Lattice Boltzmann Method on Many Integrated Core Processors

This paper puts forward an efficient Lattice Boltzmann method for use as a wake simulator suitable for real-time environments. The method is limited to low speed incompressible flow but is very efficient and can be used to compute flows “on the fly”. In particular, many-core machines allow for the method to be used with the need of very expensive parallel clusters. Results are shown here for flows around cylinders and simple ship shapes

Real Time Wake Computations using Lattice Boltzmann Method on Many Integrated Core Processors

This paper puts forward an efficient Lattice Boltzmann method for use as a wake simulator suitable for real-time environments. The method is limited to low speed incompressible flow but is very efficient and can be used to compute flows “on the fly”. In particular, many-core machines allow for the method to be used with the need of very expensive parallel clusters. Results are shown here for flows around cylinders and simple ship shapes

Finite Volume vs.vs. Streaming-based Lattice Boltzmann algorithm for fluid-dynamics simulations: a one-to-one accuracy and performance study

A new finite volume (FV) discretisation method for the Lattice Boltzmann (LB) equation which combines high accuracy with limited computational cost is presented. In order to assess the performance of the FV method we carry out a systematic comparison, focused on accuracy and computational performances, with the standard $streaming$ (ST) Lattice Boltzmann equation algorithm. To our knowledge such a systematic comparison has never been previously reported. In particular we aim at clarifying whether and in which conditions the proposed algorithm, and more generally any FV algorithm, can be taken as the method of choice in fluid-dynamics LB simulations. For this reason the comparative analysis is further extended to the case of realistic flows, in particular thermally driven flows in turbulent conditions. We report the first successful simulation of high-Rayleigh number convective flow performed by a Lattice Boltzmann FV based algorithm with wall grid refinement.Comment: 15 pages, 14 figures (discussion changes, improved figure readability