Flow past a rectangular cylinder in a stratified fluid

2014

Numerical calculations of flow around a square cylinder are presented using the multi-relaxation-time lattice Boltzmann method at Reynolds number 150. The effects of upstream locations, downstream locations and blockage are investigated systematically. A detail analysis are given in terms of time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualizations and phase diagrams. A number of physical quantities mean drag coefficient, drag coefficient, Strouhal number and root-mean-square values of drag and lift coefficients are calculated and compared with the well resolved experimental data and numerical results available in open literature. The results had shown that the upstream, downstream and height of the computational domain are at least 7.5, 37.5 and 12 diameters of the cylinder, respectively.

2019

An overview of the Lattice Boltzmann Method has been presented with an in house algorithm for the numerical simulation of fluid flow around a circular cylinder. The linearization of the collision operator has been discussed for distributions not close to the local equilibrium state, and numerical simulation has been carried out for stable initial conditions up to a Reynolds number of 80. An overview of the lattice gas automata with regard to Boolean variables describing the particle occupation has also been defined. A comparison between the data obtained from the two dimensional fluid flow around the cylinder and previous experimentation has also been made.

Journal of The Brazilian Society of Mechanical Sciences and Engineering, 2020

In this work, the lattice Boltzmann (LB) method was applied to simulate incompressible steady and unsteady low Reynolds number (Re) flows around a confined cylinder. In the LB method, different collision models (Bhatnagar-Gross-Krook model, two-relaxation-time model, multi-relaxation-time model, and entropic lattice Boltzmann model) and a regularization model were used, and the results were compared. Numerical results pertaining to a two-dimensional flow around a cylinder are reported and compared with numerical and experimental data available in the literature. The results agree with the predictions made from the literature. A correlation for Strouhal number (St) for 55 ≤ Re ≤ 300 is suggested.

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Journal of Non-Newtonian Fluid Mechanics, 2011

A second-order lattice Boltzmann algorithm is used for Power-Law non-Newtonian flow simulation. The shear dependent behavior of the fluid is implemented through calculating the shear locally from the lattice distribution functions. A step by step verification procedure is taken to ensure the accuracy and the physical correctness of the numerical simulation. The flow past a series of tandem arrangement of two cylinders is computed in a confined domain. The effects of Reynolds number, the Power-Law index, and the distance between two cylinders on both the flow field and the drag coefficients of the cylinders are examined in detail.

Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2018

Numerical simulations are performed, in the range of 0.5 B g B 5, where g is the separation ratio between the cylinders at fixed Reynolds number 150 and aspect ratio 2, for flow past five side-by-side rectangular cylinders. A two-dimensional code is developed using the lattice Boltzmann method. The effect of separation ratio on the vortex shedding frequency, time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficients and force statistics exerted on the cylinders is quantified together with the observed flow structure. Five different flow structures were found and named as nearly symmetric (g = 0.5), flip-flopping (g = 1), modulated (g = 1.5), strongly interactive (g = 2, 2.5 and 3) and weakly interactive (g = 4 and 5) flow structures. It is found that the vortices are generated on the surfaces of the cylinders as width of the cylinder is 2h (h is the width of the rectangular cylinders) and due to this there is modulation in time-history analysis of drag and lift coefficients for all chosen cases except at g = 0.5. The Strouhal number is also calculated using Welch's method for comparison, and correlation of lift coefficients for different combinations is also given.

… journal of heat and fluid flow, 2000

International Journal of Modern Physics C, 2004

Minimal Boltzmann kinetic models, such as lattice Boltzmann, are often used as an alternative to the discretization of the Navier-Stokes equations for hydrodynamic simulations. Recently, it was argued that modeling sub-grid scale phenomena at the kinetic level might provide an efficient tool for large scale simulations. Indeed, a particular variant of this approach, known as the entropic lattice Boltzmann method (ELBM), has shown that an efficient coarse-grained simulation of decaying turbulence is possible using these approaches. The present work investigates the efficiency of the entropic lattice Boltzmann in describing flows of engineering interest. In order to do so, we have chosen the flow past a square cylinder, which is a simple model of such flows. We will show that ELBM can quantitatively capture the variation of vortex shedding frequency as a function of Reynolds number in the low as well as the high Reynolds number regime, without any need for explicit sub-grid scale modeling. This extends the previous studies for this set-up, where experimental behavior ranging from Re ∼ O(10) to Re ≤ 1000 was predicted by a single simulation algorithm. 1-5

Journal of Computational Physics, 2009

We apply the lattice Boltzmann equation (LBE) with multiple-relaxation-time (MRT) collision model to simulate laminar flows in two-dimensions (2D). In order to simulate flows in an unbounded domain with the LBE method, we need to address two issues: stretched nonuniform mesh and inflow and outflow boundary conditions. We use the interpolated grid stretching method to address the need of non-uniform mesh. We demonstrate that various inflow and outflow boundary conditions can be easily and consistently realized with the MRT-LBE. The MRT-LBE with non-uniform stretched grids is first validated with a number of test cases: the Poiseuille flow, the flow past a cylinder asymmetrically placed in a channel, and the flow past a cylinder in an unbounded domain. We use the LBE method to simulate the flow past two tandem cylinders in an unbounded domain with Re = 100. Our results agree well with existing ones. Through this work we demonstrate the effectiveness of the MRT-LBE method with grid stretching.

Computers & Mathematics with Applications, 2019

In order to study the flow behavior at high Reynolds numbers, two modified models, known as the multiple-relaxation-time lattice Boltzmann method (MRT-LBM) and largeeddy-simulation lattice Boltzmann method (LES-LBM), have been employed in this paper. The MRT-LBM was designed to improve numerical stability at high Reynolds numbers, by introducing multiple relaxation time terms, which consider the variations of density, energy, momentum, energy flux and viscous stress tensor. As a result, MRT-LBM is capable of dealing with turbulent flows considering energy dispersion and dissipation. In the present paper, this model was employed to simulate the flow at turbulent Reynolds numbers in wall-driven cavities. Two-sided wall driven cavity flow was studied for the first time, based on MRT-LBM, at Reynolds numbers ranging from 2 × 10 4 to1 × 10 6 , and employing a very large resolution2048 × 2048. It is found that whenever top and bottom lids are moving in the opposite directions, and the Reynolds number is higher than 2 ×10 4 , the flow is chaotic, although some quasi-symmetric properties still remain, fully disappearing at Reynolds numbers between 2 × 10 5 and 3 × 10 5. Furthermore, between this Reynolds numbers range, 2 × 10 5 <Re< 3 × 10 5 , the quasi-symmetric structures turn into a much smaller and fully chaotic eddies. The LES-LBM model implements the large eddy simulation turbulent model into the conventional LBM, allowing to study the flow at turbulent Reynolds numbers. LES-LBM combined with Quadruple-tree Cartesian cutting grid (tree grid) was employed for the first time to characterize the flow dynamics over a cylinder and a hump, at relatively high Reynolds numbers. In order to construct the macroscopic quantities in the virtual boundaries separating two different grid levels, a set of new schemes were designed. The coupling of the LES-LBM and tree grid drastically reduced the computational time required to perform the simulations, thus, allowing to minimize the hardware requirements. LES-LBM model is shown to be much more efficient when combined with the tree grid instead of using the standard Cartesian grid.