Numerical Simulation of Flow Around Two Side-by-Side Circular Cylinders at High Reynolds Number Hamidreza Rahimi 1,2 , Xiaonan Tang 1* , Yaser Esmaeeli 3 , Ming Li 2 , Alireza Pourbakhtiar 1,2 1 Xi’an Jiaotong-Liverpool University, Suzhou 215123, China 2 University of Liverpool, Liverpool, L69 3BX, UK 3 Ferdowsi University, Mashhad, 9177948974, Iran Corresponding Author Email: Xiao.Tang@xjtlu.edu.cn https://doi.org/10.18280/ijht.380109 ABSTRACT Received: 3 April 2019 Accepted: 26 December 2019 The fluid flow around a cylinder is one of the classic issues in fluid mechanics because of its various applications. Cylindrical structures, both single and in the group patterns, are present in the design of cooling systems of nuclear power plants, hydro-structures, heat exchangers, chimneys, high buildings, power lines, cables and networks in air and water. In many engineering applications, Karman's vortex shedding produces flow-induced vibrations. To comprehend the fluid structures surrounding the cylinders, it is vital to understand some fundamental issues such as boundary layers, flow separation, free shear layer, sequence and dynamics of vortices. According to the limited studies conducted for the vertical arrangement of two cylinders in a flow with the high Reynolds number, there is no evidence of oblique flow or bi-stable pattern except in the case where cylinders are close to each other. In this paper, the impact of the vertical arrangement of two cylinders on flow with high Reynolds number has been investigated via numerical modelling. The results indicated that the flow pattern is irregular and unstable for denser arrangements while the propagation of vortices does not have any tendency in different spacing. Keywords: circular cylinder, supercritical Reynolds number, drag coefficient, lift coefficient, side- by-side arrangement 1. INTRODUCTION Since the fluid flow around a cylinder widely exits and has many different applications, its study has drawn great attention to many researchers. There are many studies on the flow around an isolated single circular cylinder, such as papers [1- 7] and monographs [8-10]. Cylindrical structures can be found in either single or group patterns, e.g. in the designs of cooling systems of nuclear power plants, hydro-structures, heat exchangers, chimneys, high buildings, power lines, cables and networks in air and water. In many engineering applications Karman vortex shedding is sensible for problems with flow- induced vibration and noise. A comprehensive study has been done on the fluid dynamics for the flow around a circular cylinder, including fundamental topics such as the boundary layer, separation, the free shear layer, the wake and the dynamics of vortices. Therefore, fluid dynamics of the multiple immersed cylinders in a uniform vertical flow has been studied by many researchers. One of the first experimental studies on two cylinders in a longitudinal and vertical arrangement was conducted by Biermann and Herrnstein [11]. Studies on behaviour of the flow in vicinity of the cylinder group in the vertical flow have been reviewed by researchers [12-15], and a recent major review in this regard was given by Sumner [16]. Furthermore, many experimental studies have been carried out on cylinders with the vertical arrangement in a steady horizontal flow, which varies from low Reynolds number (Re=50) to high Reynolds number (Re=6.5x10 5 ). Some experimental studies have been done on three cylinders with the vertical arrangement, for example the studies [17-25]. Study on a large number of cylinders in a single-row vertical arrangement has also been undertaken by researchers [26-30]. The results of such studies indicated that in such cases, the flow pattern is disordered, which is due to the mixing and the deviation of the flow through empty space between the cylinders, especially where T / D <2, where T is the distance between the centers of two cylinders and D is the diameter of the cylinders. Flow through empty space between the cylinders may frequently alternate, resulting in intermittent mixing of different jets passing through the cylinders. This feature has led to the flow pattern called “Metastable" [29]. In numerical analysis, studies have also been conducted on the flow around two cylinders in a vertical arrangement, which is mainly in lower Reynolds numbers [16], including the studies conducted by Chang and Song [31] for Re=100, [32] for Re=200, [33] for Re=100, 200, and [34] for Re=750. Cylinders in different shapes and geometries are widely used in different engineering and modeling topics such as cooling system, pin-fins, vegetation. The flow around cylinders has continuously been investigated by numerous researchers to enhance the understanding of hydraulic properties of cylinders. Many researchers consider the relationship between the performance and geometry based on traditional circular dowels in common shape, such as of variable shapes [35, 36], different arrangements [37, 38] and geometric parameters [39-41] of cylinders. Additionally, several perforated features such as pin-fins are conceived to achieve favorable hydraulic and thermal performance. Results of relevant research indicate that there is a strong correlation between morphological feature and performance, such as the numbers or shapes of holes [42-44]. However, it seems International Journal of Heat and Technology Vol. 38, No. 1, March, 2020, pp. 77-91 Journal homepage: http://iieta.org/journals/ijht 77