A computational study of drag reduction and vortex shedding suppression of flow past a square cylinder in presence of small control cylinders

Abstract

This article presents a two-dimensional numerical study of the unsteady laminar flow from a square cylinder in presence of multiple small control cylinders. The cylinders are placed in an unconfined medium at low Reynolds numbers (Re = 100 and 160). Different flow phenomena are captured for the gap spacings (g = s/D, where s is the surface-to-surface distance between the main cylinder and small control cylinders and D is the size of the main cylinder) between 0.25 – 3 and angle of attack (θ) ranging from 300 to 1800. Numerical calculations are performed by using a lattice Boltzmann method. In this paper, the important flow physics of different observed flow patterns in terms of instantaneous vorticity contours visualization, time-trace analysis of drag and lift coefficients and power spectra analysis of lift coefficient are presented and discussed. Drag reduction and suppression of vortex shedding is also discussed in detail and compared with the available experimental and numerical results qualitatively as well as quantitatively. In addition, the mean drag coefficient, Strouhal number, root-mean-square values of the drag and lift coefficients are determined and compared with a single square cylinder without small control cylinders. We found that the drag is reduced 99.8% and 97.6% for (θ, g) = (300, 3) at Re = 100 and 160, respectively.

High Reynolds number unsteadiness assessment using 3D and 2D computational fluid dynamics simulations of a thick aerofoil equipped with a spoiler

“…Although the aerofoil is 60% thick, this behaviour falls in line with the well-known cylinder behaviour: C L carries the main frequency while C D carries the first harmonics and is always twice as high as the peak frequency. 35 In the wake, both information are available through the air velocity and therefore the main frequency and harmonics are seen.…”

Fluid flow and heat transfer around square cylinder with dual splitter plates arranged at novel positions

“…A maximum of nearly 100% reduction on the drag of a square cylinder was achieved by using the control cylinders at Re = 100. 17 In addition, when two square cylinders are arranged at the tandem position, it is found that the downstream cylinder experiences less drag force than the upstream cylinder; however, the r.m.s lift coefficient is more on the downstream cylinder in the range of Re = 75–150. 18 It is also observed for steady flow over a plain square cylinder placed in a channel with a cavity that the lift coefficient can be negative or positive depending on the forces acting on the top and bottom faces of the cylinder.…”

“…A small control cylinder and/or multiple control cylinders are also efficient to reduce the fluid forces and vortex shedding around a square cylinder. [15][16][17] The arrangement of the control cylinder alters the flow regime, and accordingly, the drag force changes. A maximum of nearly 100% reduction on the drag of a square cylinder was achieved by using the control cylinders at Re = 100.…”

Numerical Simulation of Drag Reduction on a Square Rod Detached with Two Control Rods at Various Gap Spacing via Lattice Boltzmann Method

“…The authors reported that g = 2 is the optimum space and the maximum reduction in drag force was examined at g = 0. Islam et al [14] examined the influence of Reynolds number on flow over a square rod using passive control method for small, moderate, and wide gap spacings. They found maximum reduction in force coefficients at closely gapped spacing and observed fully developed flow at moderate and wide gap spacings.…”