Two-dimensional numerical study of vortex shedding regimes of oscillatory flow past two circular cylinders in side-by-side and tandem arrangements at low Reynolds numbers

2014 ◽  
Vol 751 ◽  
pp. 1-37 ◽  
Author(s):  
Ming Zhao ◽  
Liang Cheng
Keyword(s):  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
The Other ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Low Reynolds Numbers ◽  
Single Cylinder ◽  
Gap Ratio

AbstractOscillatory flow past two circular cylinders in side-by-side and tandem arrangements at low Reynolds numbers is simulated numerically by solving the two-dimensional Navier–Stokes (NS) equations using a finite-element method (FEM). The aim of this study is to identify the flow regimes of the two-cylinder system at different gap arrangements and Keulegan–Carpenter numbers (KC). Simulations are conducted at seven gap ratios $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}G$ ($G=L/D$ where $L$ is the cylinder-to-cylinder gap and $D$ the diameter of a cylinder) of 0.5, 1, 1.5, 2, 3, 4 and 5 and KC ranging from 1 to 12 with an interval of 0.25. The flow regimes that have been identified for oscillatory flow around a single cylinder are also observed in the two-cylinder system but with different flow patterns due to the interactions between the two cylinders. In the side-by-side arrangement, the vortex shedding from the gap between the two cylinders dominates when the gap ratio is small, resulting in the gap vortex shedding (GVS) regime, which is different from any of the flow regimes identified for a single cylinder. For intermediate gap ratios of 1.5 and 2 in the side-by-side arrangement, the vortex shedding mode from one side of each cylinder is not necessarily the same as that from the other side, forming a so-called combined flow regime. When the gap ratio between the two cylinders is sufficiently large, the vortex shedding from each cylinder is similar to that of a single cylinder. In the tandem arrangement, when the gap between the two cylinders is very small, the flow regimes are similar to that of a single cylinder. For large gap ratios in the tandem arrangement, the vortex shedding flows from the gap side of the two cylinders interact and those from the outer sides of the cylinders are less affected by the existence of the other cylinder and similar to that of a single cylinder. Strong interaction between the vortex shedding flows from the two cylinders makes the flow very irregular at large KC values for both side-by-side and tandem arrangements.

Oscillatory flow regimes around four cylinders in a square arrangement under small and conditions

2015 ◽  
Vol 769 ◽  
pp. 298-336 ◽  
Author(s):  
Feifei Tong ◽  
Liang Cheng ◽  
Ming Zhao ◽  
Hongwei An
Keyword(s):  
Flow Field ◽  
Oscillatory Flow ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Hydrodynamic Forces ◽  
Circular Cylinders ◽  
Single Cylinder ◽  
Wake Interference ◽  
Spatio Temporal

Sinusoidally oscillatory flow around four circular cylinders in an in-line square arrangement is numerically investigated at Keulegan–Carpenter numbers ($\mathit{KC}$) ranging from 1 to 12 and at Reynolds numbers ($\mathit{Re}$) from 20 to 200. A set of flow patterns is observed and classified based on known oscillatory flow regimes around a single cylinder. These include six types of reflection symmetry regimes to the axis of flow oscillation, two types of spatio-temporal symmetry regimes and a series of symmetry-breaking flow patterns. In general, at small gap distances, the four structures behave more like a single body, and the flow fields therefore resemble those around a single cylinder with a large effective cylinder diameter. With increasing gap distance, flow structures around each individual cylinder in the array start to influence the overall flow patterns, and the flow field shows a variety of symmetry and asymmetry patterns as a result of vortex and shear layer interactions. The characteristics of hydrodynamic forces on individual cylinders as well as on the cylinder group are also examined. It is found that the hydrodynamic forces respond in a similar manner to the flow field to the cylinder proximity and wake interference.

Numerical Simulation of Vortex-Induced Vibration of Two Rigidly Connected Cylinders in Side-by-Side and Tandem Arrangements Using RANS Model

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Ming Zhao ◽  
Joshua M. Murphy ◽  
Kenny Kwok
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Response Amplitude ◽  
Maximum Response ◽  
Circular Cylinders ◽  
Tandem Arrangement ◽  
Vortex Induced Vibration ◽  
Single Cylinder ◽  
Gap Ratio ◽  
G Ratio

Vortex-induced vibration (VIV) of two rigidly connected circular cylinders in side-by-side and tandem arrangements in the cross-flow direction was investigated using two-dimensional (2D) numerical simulations. The 2D Reynolds-Averaged Navier–Stokes (RANS) equations were solved for the flow, and the equation of the motion was solved for the response of the cylinders. Simulations were conducted for a constant mass ratio of 2.5, gap ratios G (ratio of the gap between the cylinders to the cylinder diameter) in the range of 0.5 to 3, and reduced velocities in the range of 1 to 30. The effects of the gap ratio on the response of the cylinders were analyzed extensively. The maximum response amplitude in the lock-in regime was found to occur at G = 0.5 in the side-by-side arrangement, which is about twice that of a single cylinder. In the side-by-side arrangement, the response regime of the cylinders for gap ratios of 1.5, 2, 2.5, and 3 is much narrower than that of a single cylinder, because the vortex shedding from the two cylinders is in an out-of-phase pattern at large reduced velocities. In the tandem arrangement, the maximum response amplitude of the cylinders is greater than that of a single cylinder for all the calculated gap ratios. For the gap ratio of 0.5 in the tandem arrangement, the vortex shedding frequency from the upstream cylinder was not observed in the vibration at large reduced velocities, and the response is galloping.

An Approximate Method for the Drags of Two-Dimensional Obstacles at Low Reynolds Numbers

1996 ◽  
Vol 63 (4) ◽  
pp. 990-996 ◽  
Author(s):  
Hideo Yano ◽  
Katsuya Hirata ◽  
Masanori Komori
Keyword(s):  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Governing Equations ◽  
Simple Method ◽  
Drag Coefficients ◽  
Low Reynolds Numbers ◽  
Singularity Method ◽  
Experimental Values ◽  
Discrete Singularity Method

We propose a new simple method of computing the drag coefficients of two-dimensional obstacles symmetrical to the main-flow axis at Reynolds numbers less than 100. The governing equations employed in this method are the modified Oseen’s linearized equation of motion and continuity equation, and the computation is based on a discrete singularity method. As examples, simple obstacles such as circular cylinders, rectangular prisms, and symmetrical Zhukovskii aerofoils are considered. And it was confirmed that the computed drags agree well with experimental values. Besides optimum shapes of these geometries, which minimize the drag coefficients, are also determined at each Reynolds number.

Feedback control of vortex shedding at low Reynolds numbers

1993 ◽  
Vol 248 ◽  
pp. 267-296 ◽  
Author(s):  
Kimon Roussopoulos
Keyword(s):  
Feedback Control ◽  
Vortex Shedding ◽  
Single Channel ◽  
Water Channel ◽  
Open Water ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Low Reynolds Numbers ◽  
Wake Instability ◽  
Low Reynolds

This paper describes experiments undertaken to study in detail the control of vortex shedding from circular cylinders at low Reynolds numbers by using feedback to stabilize the wake instability. Experiments have been performed both in a wind tunnel and in an open water channel with flow visualization. It has been found that feedback control is able to delay the onset of the wake instability, rendering the wake stable at Reynolds numbers about 20% higher than otherwise. At higher flow rates, however, it was not possible to use single-channel feedback to stabilize the wake - although, deceptively, it was possible to reduce the unsteadiness recorded by a near-wake sensor. When control is applied to a long span only the region near the control sensor is controlled. The results presented in this paper generally support the analytical results of other researchers.

scholarly journals FORCES ON ROUGH-WALLED CIRCULAR CYLINDERS

1976 ◽  
Vol 1 (15) ◽  
pp. 134 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Least Squares Method ◽  
Reynolds Numbers ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Mean Square ◽  
Relative Roughness

This paper presents the results of an extensive experimental investigation of the in-line and transverse forces acting on sand-roughened circular cylinders placed in oscillatory flow at Reynolds numbers up to 1,500,000, Keulegan-Carpenter numbers up to 100, and relative roughnesses from 1/800 to 1/50. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least squares method. The transverse force (lift) has been analysed in terms of its maximum and root-mean-square values. In addition, the frequency of vortex shedding and the Strouhal number have been determined. The results have shown that all of the coefficients cited above are functions of the Reynolds number, Keulegan-Carpenter number, and the relative roughness height. The results have also shown that the effect of roughness is quite profound and that the drag coefficients obtained from tests in steady flow are not applicable to harmonic flows even when the loading is predominantly drag.

Vortex shedding from circular cylinders at low Reynolds numbers

1971 ◽  
Vol 46 (4) ◽  
pp. 749-756 ◽  
Author(s):  
M. Gaster
Keyword(s):  
Cross Section ◽  
Vortex Shedding ◽  
Circular Cross Section ◽  
Reynolds Numbers ◽  
Similar Type ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Wake Structure ◽  
Low Reynolds Numbers ◽  
Cell Shedding

Experiments on slightly tapered models of circular cross-section have shown that the vortex wake structure exists in a number of discrete cells having different shedding frequencies. Within each cell shedding is regular and periodic, the frequency being somewhat lower than that from a parallel cylinder of the same diameter. A similar type of wake behaviour has also been observed on a parallel model in a non-uniform mean flow. These results suggest that the discontinuities in the shedding law observed by Tritton could arise through non-uniformities in the flow.

scholarly journals Oblique and parallel modes of vortex shedding in the wake of a circular cylinder at low Reynolds numbers

1989 ◽  
Vol 206 ◽  
pp. 579-627 ◽  
Author(s):  
C. H. K. Williamson
Keyword(s):  
Reynolds Number ◽  
Boundary Conditions ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Completely Continuous ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Central Flow

Two fundamental characteristics of the low-Reynolds-number cylinder wake, which have involved considerable debate, are first the existence of discontinuities in the Strouhal-Reynolds number relationship, and secondly the phenomenon of oblique vortex shedding. The present paper shows that both of these characteristics of the wake are directly related to each other, and that both are influenced by the boundary conditions at the ends of the cylinder, even for spans of hundreds of diameters in length. It is found that a Strouhal discontinuity exists, which is not due to any of the previously proposed mechanisms, but instead is caused by a transition from one oblique shedding mode to another oblique mode. This transition is explained by a change from one mode where the central flow over the span matches the end boundary conditions to one where the central flow is unable to match the end conditions. In the latter case, quasi-periodic spectra of the velocity fluctuations appear; these are due to the presence of spanwise cells of different frequency. During periods when vortices in neighbouring cells move out of phase with each other, ‘vortex dislocations’ are observed, and are associated with rather complex vortex linking between the cells. However, by manipulating the end boundary conditions, parallel shedding can be induced, which then results in a completely continuous Strouhal curve. It is also universal in the sense that the oblique-shedding Strouhal data (Sθ) can be collapsed onto the parallel-shedding Strouhal curve (S0) by the transformation, S0 = Sθ/cosθ, where θ is the angle of oblique shedding. Close agreement between measurements in two distinctly different facilities confirms the continuous and universal nature of this Strouhal curve. It is believed that the case of parallel shedding represents truly two-dimensional shedding, and a comparison of Strouhal frequency data is made with several two-dimensional numerical simulations, yielding a large disparity which is not clearly understood. The oblique and parallel modes of vortex shedding are both intrinsic to the flow over a cylinder, and are simply solutions to different problems, because the boundary conditions are different in each case.

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