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The flow around two square cylinders arranged side by side has been investigated through lattice Boltzmann method under different Reynolds numbers and various space ratios (s = d/D, d is the separation distance between two cylinders, D is the characteristic length) from 1.0, 1.1 to 2.7, including 18 space ratios. It is found that the flip-flop regime occurs at small space ratios and the synchronized regime occurs at large space ratios. Wide and narrow wakes at small spacing are formed and intermittently change behind the cylinders, and the biased flow in the gap is bistable. The frequency of vortex shedding is different in two wakes. The upper frequency is smaller than the lower frequency for small space ratios (s < 1.4), and the time-averaged drag and lift coefficients of cylinders are also different. When the space ratios increase, two distinct vortex streets occur behind the cylinders, and the frequency of vortex shedding is almost equal in two wakes. Also the difference of time-averaged drag and lift coefficients of the cylinders decreases with the increase in space ratios; in this case the flow shows synchronized regime. The transition between flip-flop and synchronized regimes occurs at s = 1.5. When s < 1.5, the flow shows flip-flop regime; otherwise, it shows synchronized regime. When s = 2.0 and 2.5, the curves for the time-averaged drag and lift coefficient with different Reynolds numbers are smooth. When s = 1.5 and 1.8, the curves are also smooth under Re ≤ 140, but that will be fluctuant under Re > 140 because of the nonlinear interaction between the wakes, and the instability of flow becomes stronger with the increase in Reynolds numbers. On the other hand, the vortex shedding type from the cylinder occurs in-phase when s < 2.5 and s = 2.5 for Re < 190, whereas that occurs anti-phase when s = 2.5 for Re ≥190. In addition, the pressure varies a little on the left surfaces and greatly on the right surfaces of both cylinders with the increase in Reynolds number at s = 2.5.

A numerical investigation is carried out to analyze the flow patterns, drag and lift coefficients, and vortex shedding around a square cylinder using a control circular bar upstream and downstream. Lattice Boltzmann method (LBM) was used to investigate flow over a square cylinder controlled by upstream and downstream circular bar, which is the main novelty of this study. Compared with those available results in the literature, the code for flow over a single square cylinder proves valid. The Reynolds number (Re) based on the width of the square cylinder ($D$) and diameter of circular bar ($d$) are 100 for square cylinder, 30 and 50 for different circular bars. Numerical simulations are performed in the ranges of $1\le L∕D\le 5$ and $1\le G∕D\le 5$, where $L$ and $G$ are the center-to-center distances between the bar and cylinder. Five distinct flow patterns are observed in the present study. It is found that the maximum percentage reduction in drag coefficient is 59.86% by upstream control bar, and the maximum percentage reduction in r.m.s. lift coefficient is 73.69% by downstream control bar. By varying the distance ratio for the downstream control bar, a critical value of distance ratio is found where there are two domain frequencies.

In this paper, effects of nondimensional distance between two square cylinders on the dissipation characteristics of the complex flow are investigated. The viscosity entropy generation rates around two serial square cylinders and the lift coefficient are analyzed to fully reveal the statistical features of the flow dissipation. Numerical results mainly show that the major viscosity entropy generation rate appears in the shear intersection region of the main flow and local stationary vortex. The viscosity entropy generation rate increases with increasing nondimensional distance ($S^{\ast }$). The increasing slope of the viscosity entropy generation rate at a range of $S^{\ast }\le 2$ is greater than that of $2\le S^{\ast }\le 5$. It is also found that the viscosity entropy generation rate is kept as a constant when the nondimensional distance $S^{\ast }$ is greater than 5. At $S^{\ast }\ge 5$, the effect of downstream square cylinder becomes negligible on the viscosity entropy generation rate. The fluctuating amplitude increases with increasing the nondimensional distance $S^{\ast }$. The high-frequency peak is ascribed to the strong vortex shedding around the downstream square cylinder, and the low-frequency peak is ascribed to the weak vortex shedding around the up square cylinder at $S^{\ast }=1$. Although our focus is mainly on the complex flow around two square cylinders, this work demonstrates the viscosity entropy generation rate with increasing nondimensional distance, which provides nice physical insight into understanding the local flow dissipation characteristics around the two serial square cylinders.

This study aims to numerically investigate the optimal conditions for fluid flow control around a single square cylinder with the help of a pair of attached flat plates. It is comparatively a new approach for controlling fluid flows as compared to the traditional solo plate flow control devices. The plates are attached adjacent to the both rear corners of the cylinder and their length (l) is varied from $0.1$ to 4 times size of main cylinder while fixing the height (h) at $0.2$. By varying the length, the plates manage to control the flow gradually. This study discusses how a steady wake can be achieved through control plates. Results indicate that the flow regime changes from unsteady to transitional at $l=2.7$ while for $l>3.1$ the steady flow appears. The streamlines visualizations reveal different flow structures termed as the oval-eye vortex, chain necklace vortex, sphere vortex, hair pin vortex and wooden eyes vortex-like structures. Among these the oval-eye vortex structure is found to have higher flow induced forces and shedding frequencies while the wooden eyes vortex structure is found to have minimal flow induced forces and shedding frequencies. After $l=3.2$, the plates’ efficacy is proven by a 100$\%$ reduction in Strouhal number, root-mean-square values of lift coefficient and amplitudes of lift and drag coefficients. This study reveals that $l=3.2$ is the best optimal value of plates length for complete wake and fluid forces control.

Numerical study of impulsively started flow over two tandem square cylinders where former cylinder is rotated at angles (0-45deg) to main stream flow direction keeping later one inline to flow stream with a separation of twice the side length of square prism between the centers of cylinders is performed using FVM code solver FLUENT 6.3.26. Temporal developments of streamlines around cylinders are studied for laminar flow regime (Re = 100). Flow pattern formed are categories into Type-1, Type-2, Type-3 & Type-4 as per vortices growth at corresponding angle of incidence which are novel results of present study. Pressure distributions over the surface of cylinders are also monitored.

In this paper, we discuss the applicability of a numerical wave channel CADMAS-SURF/3D with regard to hydrodynamics on a salt marsh by comparing numerical experimental results with previous studies for both flow and wave conditions. The present results indicate that the model is promising as long as appropriate values for numerical parameters such as the grid size are used. We present results for the bottom velocity and turbulence kinetic energy around a cylinder which are important understanding deposition in salt marsh vegetations. Furthermore, this paper shows that the drag coefficient and inertia coefficient for circular cylinders in waves depend on the density of the cylinders.

When modelling a flow in the atmosphere and the processes strongly influenced by it (e.g., the dispersion of air pollution), it is important to appreciate that the properties of both the flow itself and the dispersion are affected by the flow regime; i.e., whether the flow is turbulent (as is almost always the case in the atmosphere) or laminar. A second factor that might complicate atmospheric flow is stability, which depends on the nature of vertical temperature stratification.

In the first part of this chapter, we demonstrate the impact of vertical temperature stratification on flow structure, modelled via the Boussinesq approximation and by varying the Froude number (Fr). The flow is assumed to be laminar and is modelled in 2D.

Next, we review several approaches to treating turbulence in modelling studies, with an emphasis on an implicit large-eddy simulation. The results of Taylor—Green vortex computations performed using this method are compared with the results of a direct numerical simulation at moderate Reynolds numbers. Several quantities are considered, including the kinetic energy dissipation rate, probability density functions of turbulent fluctuations, and 3D energy spectra.