Laminar flow past two rotating circular cylinders in a side-by-side arrangement

Abstract

For the purpose of a careful analysis of the modification of flow by the combined effects of the rotation and the spacing between two cylinders on the flow, numerical simulations are performed at a various range of absolute rotational speeds ͉͑␣ ͉ Յ 2͒ for four different gap spacings of 3, 1.5, 0.7, and 0.2 at one Reynolds number of 100 showing the typical two-dimensional vortex shedding. As ͉␣͉ increases, flow becomes stabilized and finally a steady state beyond the critical rotational speed depending on the gap spacing. In the cases of gap spacings of 3 and 0.2, the wake patterns keep the antiphase-synchronized pattern and the single bluff body pattern, respectively, until flow reaches the steady state. However, for the gap spacings of 1.5 and 0.7, the wake patterns change in the unsteady regime. For the gap spacing of 1.5, the wake pattern shows in-phase-synchronized, flip-flop and antiphase-synchronized patterns in turn according to ͉␣͉. For the gap spacing of 0.7, the flip-flopping wake pattern is changed as the in-phase-synchronized pattern behind the cylinder with the one-row vortex street in downstream with increasing ͉␣͉.This brief communication aims at a careful identification of flow patterns, characterized by the behavior of the wake region, around two rotating circular cylinders in a side-byside arrangement.The flow around two stationary circular cylinders of equal diameter arranged side-by-side has been extensively investigated in the past 1-19 because it can be considered that an elementary flow is helpful for understanding the flow patterns and aerodynamic characteristics around multiple bluff bodies in engineering practice. It is now well known that the wake behind the two side-by-side cylinders depends significantly on the normalized gap spacing, g * = g / D, where g and D are the distance between two cylinder surfaces and the cylinder diameter, respectively.Sumner et al. 8 briefly tabulated the measured quantities according to previous experiments in company with the experimental conditions such as Reynolds number, g * and type of measure. They also confirmed the three basic flow patterns of the single bluff body pattern at 0 Յ g * Ͻ 0.2, the biased flow at 0.2Յ g * Յ 1.2, and the symmetric flow with either antiphase or in-phase synchronized vortex shedding at 1.2 Յ g * Յ 3.5 which have been observed by other researchers. Recently, Kang 19 numerically observed the six kinds of wake patterns over the ranges of 40Յ ReՅ 160 and g * Ͻ 5.The flow past a rotating cylinder can be considered as the elementary problem to the present topic. The rotation of a cylinder has been adopted not only to understand the wake dynamics but also to control the vortical structure in the wake by the numerous researches. As a parameter representing this problem, ␣ is the rotational speed at the cylinder surface normalized by the freestream velocity, accordingly ␣ is defined as ␣ = ⍀D / 2U ϱ , where ⍀ is the angular velocity of the cylinder. The other important parameter is the Reynolds number. Recently, Kang et al., 3...

Vortex suppression and drag reduction in the wake of counter-rotating cylinders

“…At the lowest Reynolds number investigated, Re = 100, the vortices shed by the cylinder pair coalesced to form a single von Kármán vortex street, shown in figure 7. This phenomenon was also observed at the same Reynolds number by Yoon et al (2007) for g * = 0.7. In the case of a non-rotating cylinder pair, the single vortex street shedding mode is only observed at smaller gap spacings (g * = 0.4), as found by Kang (2003), so that counter-rotation of the cylinders increases the allowable gap spacing to achieve this particular mode.…”

“…The results presented by Yoon et al (2007) and the current investigation only have one point of overlap (Re = 100, g * = 3), but in both studies the critical vortex suppression was found to be 1.7. However, as seen in the figure 21, there is a small region of instability at speeds above Ω crit .…”

“…When the two cylinders are put into counter-rotation, several recent numerical studies have shown that these wake instabilities can be attenuated and even entirely suppressed (Yoon et al 2007;Chan & Jameson 2010). Counter-rotation can be achieved in two different rotational configurations: the doublet-like and reverse doublet-like configuration, as shown in figure 2.…”

“…Counter-rotation can be achieved in two different rotational configurations: the doublet-like and reverse doublet-like configuration, as shown in figure 2. Yoon et al (2007) investigated the doublet-like configuration for a number of gap distances at Re = 100, and showed that there exists a critical rotational speed, Ω crit , where the unsteady vortex wakes are completely suppressed. Here Ω = ω/(2U/d), where ω is the rotational speed of Vortex suppression and drag reduction in the wake of counter-rotating cylinders 345 the cylinders.…”

High-Order Spectral Difference Simulation of Laminar Compressible Flow Over Two Counter-Rotating Cylinders

“…Yoon et al 9 (2007) performed simulation, with immersed boundary method, at a range of low rotational speeds for four different gap spacings at Reynolds number of 100. This method used a two-step time-split scheme, and second-order accurate central difference scheme for the spatial discretization.…”