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

Shams-Ul Islam,Shazia Kalsoom,Zia-Ul Islam,Raheela Manzoor,Zhou Chao Ying

doi:10.1063/1.4982696

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.

Highlights

A strong motivation for studying such an important practical problems come from the fact that large amplitude of lift fluctuations and alternate vortex shedding are generally design concerns for engineers
The main aim of this study is to suppress the vortex shedding and to reduce the drag and lift fluctuating amplitude of a square cylinder by passive control device using small control cylinders placed at different angles. Another main agenda of this study is to systematically examine the effect of gap spacing on wake flow structure
It is important to state here that in vorticity contours visualization graphs the positive and negative vortices are presented in the form of solid and dotted lines, respectively

Summary

Introduction

A strong motivation for studying such an important practical problems come from the fact that large amplitude of lift fluctuations and alternate vortex shedding are generally design concerns for engineers. The study of flow around square cylinder in presence of control devices is a developing hydrodynamic problem, where several rich phenomena such as modifying the near wake vortex formation region and stabilizing the near wake can be observed.[1,2] the geometry of airplanes and ships requires minimizing the drag force because of its impact on fuel consumption. Numerous attempts have so far been made for drag reduction and vortex shedding suppression over a circular cylinder using either active (requiring energy as an input) or passive (no need as an input external energy) control devices. In the available literature there is a real scarcity for the drag reduction and vortex shedding suppression for the flow past a square cylinder and to the best of the authors’ knowledge, 2158-3226/2017/7(4)/045119/19.

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Results

Conclusion