The Effect of Gap Flow on Vortex-Induced Vibration of Side-by-Side Cylinder Arrangement

2016 ◽  
Author(s):  
Bin Liu ◽  
Rajeev K. Jaiman
Keyword(s):  
Offshore Structures ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Floating Platform ◽  
Additional Time ◽  
Vortex Induced Vibration ◽  
Stable Regime ◽  
Gap Flow ◽  
Flow Induced Vibrations ◽  
Lock In

A numerical investigation of vortex-induced vibration (VIV) of a pair of identical circular cylinders placed side by side in an uniform flow has been performed. One of the cylinder is elastically mounted and only vibrates in the transverse direction, while its counterpart remains stationary. When two cylinders are placed sufficiently close to each other, a flip-flopping phenomenon can be an additional time-dependent disturbance in the range of 0.2 ≲ g* ≲ 1.2. This phenomenon was well-reported by the experimental work of Bearman and Wadcock [1] in a side-by-side circular cylinder arrangement, in which the gap flow biased toward one of the cylinders and switched the sides intermittently. Albeit one of the two cylinders is free to vibrate, this flip-flopping during VIV dynamics can still be observed. In the side-by-side arrangement, the lock-in region shrinks due to the presence of its stationary counterpart and occurs prematurely compared to that of an isolated counterpart. Similar to the tandem cylinder arrangement, in the post lock-in region, the vibration amplitude is amplified compared to the isolated counterpart. For the vibrating cylinder in the side-by-side arrangement, the biased gap flow shows a quasi-stable flow regime within the lock-in region, instead of a bi-stable regime which is reported in the stationary side-by-side arrangement. When these factors take place simultaneously, the dynamics of freely vibrating cylinder becomes complex and such a side-by-side canonical arrangement is common in offshore engineering applications, for example a floating platform operating in the side of FPSO, arrays of riser and pipelines, ships travelling in rows within close proximity and many other side-by-side operations. The chaotic fluctuation and large vibration may occur when two bluff bodies are placed closely. It often causes inevitable damages and potential risks to the offshore structures and may leads to a collision or long-term fatigue failure associated with flow-induced vibrations.

scholarly journals The wake of two side-by-side square cylinders

2011 ◽  
Vol 669 ◽  
pp. 432-471 ◽  
Author(s):  
Md MAHBUB ALAM ◽  
Y. ZHOU ◽  
X. W. WANG
Keyword(s):  
Flow Separation ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Recirculation Bubble ◽  
Vortex Interactions ◽  
Square Cylinders ◽  
Gap Flow ◽  
Spacing Ratio ◽  
Multiple Structures ◽  
Particle Imaging

Aerodynamic interference between two cylinders involves most of the generic flow features associated with multiple structures, thus providing an excellent model for gaining physical insight into the wake of multiple cylindrical structures. This work aims to provide an experimental systematic study of the flow behind two side-by-side square cylinders. The square cylinder is a representative model for bluff bodies with sharp corners, characterized by a fixed flow separation point, which are distinct from those of continuous curvature with oscillating separation points, typically represented by the circular cylinder. Experiments were performed at a Reynolds number Re of 4.7 × 104 and a cylinder centre-to-centre spacing ratio T/d (d is the cylinder height) of 1.02–6.00. The flow was measured using different techniques, including hot wires, load cell, particle imaging velocimetry and laser-induced fluorescence flow visualization. Four distinct flow regimes and their corresponding T/d ranges are identified for the first time on the basis of the flow structure and the Strouhal number. Physical aspects in each regime, such as interference between shear layers, gap flow deflection and changeover, multiple flow modes, entrainment, recirculation bubble, vortex interactions and formation lengths, are investigated in detail and are connected to the characteristics of the time-averaged and fluctuating fluid forces. The flow displays a marked difference in many facets from that behind two side-by-side circular cylinders, which is linked to their distinct flow separation natures. A crucial role played by the gap flow and its passage geometry in contributing to the observed difference is also unveiled.

Flow-Induced Vibrations of Single and Tandem Square Columns

2015 ◽  
Author(s):  
Guan Meng Zhao ◽  
Narasimha Rao Pillalamarri ◽  
Ravi Chaithanya Mysa ◽  
Rajeev K. Jaiman
Keyword(s):  
Transverse Load ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Arbitrary Lagrangian Eulerian ◽  
Response Dynamics ◽  
Tandem Arrangement ◽  
Fluid Forces ◽  
Flow Induced Vibrations ◽  
Load Component ◽  
Phase Angles

This work reports a set of numerical experiments to understand flow-induced vibrations of the square columns kept in a tandem arrangement. Results on the coupled force and response dynamics are presented for an isolated column and for a pair of square columns in the tandem configuration where downstream column is elastically mounted and free to oscillate in in-line and transverse directions. We assess the combined wake-induced and sharp-corner based galloping effects on the downstream column by comparing with the isolated square column counterpart. It is known that the circular cylinders undergo vortex-induced motion alone whereas motion of a square column is vortex-induced at low Re and galloping at high Re. The simulations are performed by means of a Petrov-Galerkin based finite-element solver using Arbitrary Lagrangian-Eulerian technique to account for the fluid mesh motion. The predicted results of the isolated column agree well with the available numerical results in the literature. The dimensions of the square columns and the domain are set in order to a have total blockage area of 5 %. The effects of reduced velocity on the fluid forces, wake contours, and the phase angles are analyzed. This work is also an attempt to enhance our understanding on the origin of wake-induced vibrations in a tandem arrangement of bluff bodies. In the case of tandem arrangement, upstream vortex shifts the stagnation point on the downstream column to the lower suction region. Thus a larger lift force is observed for the downstream column as compared to a vibrating isolated column. Phase difference between the transverse load and velocity of the downstream column determines the extent of upstream wake interaction with downstream column. When the column velocity is in-phase with the transverse pressure load component, interaction of wake vortex with the downstream column is minimum. For higher reduced velocities (Ur > 15), the wake downstream is very wide and irregular and the phase angle is consistently close to 180°.

Dynamics and stability of gap-flow interference in a vibrating side-by-side arrangement of two circular cylinders

2018 ◽  
Vol 855 ◽  
pp. 804-838 ◽  
Author(s):  
B. Liu ◽  
R. K. Jaiman
Keyword(s):  
Three Dimensional ◽  
Circular Cylinders ◽  
Dynamic Mode ◽  
Two Dimensional ◽  
Near Wake ◽  
Gap Flow ◽  
Decomposition Procedure ◽  
Wake Instability ◽  
Lock In ◽  
Flow Interference

In this work, the coupled dynamics of the gap flow and the vortex-induced vibration (VIV) of a side-by-side (SBS) arrangement of two circular cylinders is numerically investigated at Reynolds numbers $100\leqslant Re\leqslant 500$ . The influence of VIV is incorporated by allowing one of the cylinders to vibrate freely in the transverse direction, which is termed as a vibrating side-by-side (VSBS) arrangement. A comparative three-dimensional study is performed between the stationary side-by-side (SSBS) and the VSBS arrangements to examine the characteristics of the complex coupling between the VIV and the gap flow. The results are also contrasted against the isolated configurations without any proximity and gap-flow interference. Of particular interest is to establish a relationship between the VIV, the gap flow and the near-wake instability behind bluff bodies. We find that the kinematics of the VIV regulates the streamwise vorticity concentration, which accompanies a recovery of the two-dimensional hydrodynamic response at the peak lock-in. Moreover, the near-wake instability may develop around an indeterminant two-dimensional streamline saddle point along the interfaces of a pair of imbalanced counter-signed vorticity clusters. The interaction between the imbalanced vorticity clusters and the gap-flow momentum are closely interlinked with the prominence of streamwise vortical structures. In both SSBS and VSBS arrangements, the flip-flopping frequency is significantly low for the three-dimensional flow, except at the VIV lock-in for the VSBS arrangement. While an early onset of VIV lock-in is observed for the vibrating configuration, a quasi-stable deflected gap-flow regime with stably deflected gap flow is found at the peak lock-in. The increase of the gap-flow proximity interference promotes the energy transfer and stabilizes the VIV lock-in. Finally, we employ the dynamic mode decomposition procedure to characterize the space–time evolution of the vortex wake system behind the cylinders.

scholarly journals Amplitude Enhancement of Flow-Induced Vibration for Energy Harnessing

2020 ◽  
Vol 160 ◽  
pp. 01005
Author(s):  
Ze Shao ◽  
Tongming Zhou ◽  
Hongjun Zhu ◽  
Zhipeng Zang ◽  
Wenhua Zhao
Keyword(s):  
Wind Tunnel ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Flow Induced Vibration ◽  
Cross Sectional ◽  
Square Cylinders ◽  
Gap Ratio ◽  
Flow Induced Vibrations ◽  
Energy Harnessing ◽  
Single Configuration

In this paper, flow-induced vibrations of bluff bodies with four different cross-sectional geometries (circle, square, triangle and semi-circle) arranged both in single and tandem (gap ratio equals to 3 and 5) configurations are investigated in a wind tunnel. It is found that triangular and square cylinders have the higher amplitude than that of the semi-circular and the circular cylinders in the single configuration. When two cylinders are arranged in tandem, the circular cylinders have the highest amplitude among all tested cylinders. Furthermore, the semi-circular cylinder shows that its vibrating amplitude increases with the reduced velocity in the tandem system due to the galloping effect.

Surface Roughness Effects on Circular Cylinders at High Reynolds Numbers

2002 ◽  
Author(s):  
M. Eaddy ◽  
W. H. Melbourne ◽  
J. Sheridan
Keyword(s):  
Surface Roughness ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Smooth Cylinder ◽  
Lift Forces ◽  
High Reynolds ◽  
Effect Of Surface

The problem of flow-induced vibration has been studied extensively. However, much of this research has focused on the smooth cylinder to gain an understanding of the mechanisms that cause vortex-induced vibration. In this paper results of an investigation of the effect of surface roughness on the cross-wind forces are presented. Measurements of the sectional RMS fluctuating lift forces and the axial correlation of the pressures for Reynolds numbers from 1 × 105 to 1.4 × 106 are given. It was found that surface roughness significantly increased the axial correlation of the pressures to similar values found at high subcritical Reynolds numbers. There was little effect of the surface roughness on the sectional lift forces. The improved correlation of the vortex shedding means rough cylinders will be subject to larger cross-wind forces and an increased possibility of vortex-induced vibration compared to smooth cylinders.

Model reduction and mechanism for the vortex-induced vibrations of bluff bodies

2017 ◽  
Vol 827 ◽  
pp. 357-393 ◽  
Author(s):  
W. Yao ◽  
R. K. Jaiman
Keyword(s):  
Reynolds Number ◽  
Bluff Body ◽  
Low Reynolds Number ◽  
Smooth Curve ◽  
Bluff Bodies ◽  
Sharp Corner ◽  
Mass Ratio ◽  
Square Cylinder ◽  
Low Reynolds ◽  
Lock In

We present an effective reduced-order model (ROM) technique to couple an incompressible flow with a transversely vibrating bluff body in a state-space format. The ROM of the unsteady wake flow is based on the Navier–Stokes equations and is constructed by means of an eigensystem realization algorithm (ERA). We investigate the underlying mechanism of vortex-induced vibration (VIV) of a circular cylinder at low Reynolds number via linear stability analysis. To understand the frequency lock-in mechanism and self-sustained VIV phenomenon, a systematic analysis is performed by examining the eigenvalue trajectories of the ERA-based ROM for a range of reduced oscillation frequency $(F_{s})$, while maintaining fixed values of the Reynolds number ($Re$) and mass ratio ($m^{\ast }$). The effects of the Reynolds number $Re$, the mass ratio $m^{\ast }$ and the rounding of a square cylinder are examined to generalize the proposed ERA-based ROM for the VIV lock-in analysis. The considered cylinder configurations are a basic square with sharp corners, a circle and three intermediate rounded squares, which are created by varying a single rounding parameter. The results show that the two frequency lock-in regimes, the so-called resonance and flutter, only exist when certain conditions are satisfied, and the regimes have a strong dependence on the shape of the bluff body, the Reynolds number and the mass ratio. In addition, the frequency lock-in during VIV of a square cylinder is found to be dominated by the resonance regime, without any coupled-mode flutter at low Reynolds number. To further discern the influence of geometry on the VIV lock-in mechanism, we consider the smooth curve geometry of an ellipse and two sharp corner geometries of forward triangle and diamond-shaped bluff bodies. While the ellipse and diamond geometries exhibit the flutter and mixed resonance–flutter regimes, the forward triangle undergoes only the flutter-induced lock-in for $30\leqslant Re\leqslant 100$ at $m^{\ast }=10$. In the case of the forward triangle configuration, the ERA-based ROM accurately predicts the low-frequency galloping instability. We observe a kink in the amplitude response associated with 1:3 synchronization, whereby the forward triangular body oscillates at a single dominant frequency but the lift force has a frequency component at three times the body oscillation frequency. Finally, we present a stability phase diagram to summarize the VIV lock-in regimes of the five smooth-curve- and sharp-corner-based bluff bodies. These findings attempt to generalize our understanding of the VIV lock-in mechanism for bluff bodies at low Reynolds number. The proposed ERA-based ROM is found to be accurate, efficient and easy to use for the linear stability analysis of VIV, and it can have a profound impact on the development of control strategies for nonlinear vortex shedding and VIV.

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