Wake structure and evolution of flow over a finned circular cylinder

2021 ◽  
Vol 33 (7) ◽  
pp. 073613
Author(s):  
Hongjun Zhu ◽  
Wenli Liu
Keyword(s):  
Circular Cylinder ◽  
Wake Structure

scholarly journals Experimental investigation of in-line flow-induced vibration of a rotating circular cylinder

2018 ◽  
Vol 847 ◽  
pp. 664-699 ◽  
Author(s):  
J. Zhao ◽  
D. Lo Jacono ◽  
J. Sheridan ◽  
K. Hourigan ◽  
M. C. Thompson
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Rotation Rate ◽  
Free Stream ◽  
Flow Induced Vibration ◽  
Wake Structure ◽  
Rate Range ◽  
Structure System ◽  
Line Flow

This study experimentally investigates the in-line flow-induced vibration (FIV) of an elastically mounted circular cylinder under forced axial rotation in a free stream. The present experiments characterise the structural vibration, fluid forces and wake structure of the fluid–structure system at a low mass ratio (the ratio of the total mass to the displaced fluid mass) over a wide parameter space spanning the reduced velocity range $5\leqslant U^{\ast }\leqslant 32$ and the rotation rate range $0\leqslant \unicode[STIX]{x1D6FC}\leqslant 3.5$, where $U^{\ast }=U/(\,f_{nw}D)$ and $\unicode[STIX]{x1D6FC}=|\unicode[STIX]{x1D6FA}|D/(2U)$, with $U$ the free-stream velocity, $D$ the cylinder outer diameter, $f_{nw}$ the natural frequency of the system in quiescent water and $|\unicode[STIX]{x1D6FA}|$ the angular velocity of the cylinder rotation. The corresponding Reynolds number (defined by $Re=UD/\unicode[STIX]{x1D708}$, with $\unicode[STIX]{x1D708}$ the kinematic viscosity of the fluid) was varied over the interval $1349\leqslant Re\leqslant 8624$, where it is expected that the FIV response is likely to be relatively insensitive to the Reynolds number. The fluid–structure system was modelled using a low-friction air-bearing system in conjunction with a free-surface water-channel facility. Three vibration regions that exhibited vortex-induced vibration (VIV) synchronisation, rotation-induced galloping and desynchronised responses were observed. In both the VIV synchronisation and rotation-induced galloping regions, significant cylinder vibration was found to be correlated with wake–body synchronisation within the rotation rate range $2.20\lesssim \unicode[STIX]{x1D6FC}\lesssim 3.15$. Of significant interest, the frequency of the streamwise fluid force could be modulated by the imposed rotation to match that of the transverse lift force, resulting in harmonic synchronisation. Measurements using the particle image velocimetry (PIV) technique were performed to identify the wake structure. Interestingly, the imposed rotation can cause regular vortex shedding in in-line FIV at rotation rates that see suppression of the Bénard–von-Kármán vortex shedding in the case of a rigidly mounted cylinder ($\unicode[STIX]{x1D6FC}\gtrsim 1.75$). There is a monotonic increase in the drag coefficient with rotation rate beyond $\unicode[STIX]{x1D6FC}=2$ for a non-oscillating rotating cylinder. This suggests that the mechanism for sustaining the large rotation-induced galloping oscillations at higher $\unicode[STIX]{x1D6FC}$ is due to a combination of aerodynamic forcing from the locked induced vortex shedding associated with the oscillations, assisted by aerodynamic forcing, evaluated using quasi-steady theory.

Wake Structure Behind Circular Cylinder by Plasma Actuators

2011 ◽  
Author(s):  
Shunsuke Yamada ◽  
Koui Shibata ◽  
Hikaru Yanagihara ◽  
Takahiro Doi ◽  
Hitoshi Ishikawa ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Bluff Body ◽  
Three Dimensional ◽  
Plasma Actuators ◽  
Dimensional Structure ◽  
Separation Flow ◽  
Driving Frequency ◽  
Dbd Plasma ◽  
Wake Structure ◽  
Body Boundary

The separation flow causes the decrease of the driving efficiency of the fluid machines. It is important to control the separation on the bluff body, boundary layer and so on. The purpose of the present study is to control the separation on a circular cylinder and investigate the wake structure using the induced by dielectric barrier discharge (DBD) plasma. The electrode of the DBD plasma was mounted. In previous study, it is reported that the three dimensional wake structures are effective for the drag reduction. We investigate the three dimensional structure of the wake due to three dimensional jets of plasma actuators. The plasma actuators have pulse driving frequency of 0, 0.22, 1.0 and 2.0. A voltage of 4 kVpp and a frequency of 10 kHz are applied to the electrode. The velocity profiles behind the circular cylinder were measured by X type hot-wire anemometer at a Reynolds number of 1.0 × 103. The wake structure changes because the roll up of vortex is suppressed using pulse driving of the plasma actuators. The effect of plasma actuators is evaluated based on the half width and Reynolds stress in the wake.

Uniform Flow Past a Rotary Oscillating Circular Cylinder

2011 ◽  
Author(s):  
Lue Derek Du ◽  
Charles Dalton
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Uniform Flow ◽  
Resonance Phenomenon ◽  
Curvilinear Coordinates ◽  
Wake Structure ◽  
Flow Past ◽  
Wide Range

In this paper, we study uniform flow past a rotary oscillating circular cylinder computationally. The objective is to determine the effect the oscillating rotation has on the lift and drag forces acting on the cylinder, on the wake structure, and on vortex shedding. A combination of finite-difference and spectral methods is used to calculate the three-dimensional incompressible unsteady Navier-Stokes equations in primitive variable form in nonorthogonal curvilinear coordinates. Wake turbulence is modeled by an LES technique. The Reynolds number considered is Re = 1.5×104, which is the same as that in the experimental study of Tokumaru & Dimotakis (1991), who suggested this technique as a means of reducing drag. We fix the forcing amplitude at the moderate value of Ω = 2 and vary the forcing frequency in a wide range to study its effect on the flow. The resonance phenomenon and drag reduction effect are carefully examined. The wake structure and vortex shedding process is visualized by means of computational streaklines. These results have a practical application in offshore engineering.

scholarly journals Wake structure of circular cylinder in microbubble mixture

2009 ◽  
Vol 147 ◽  
pp. 012012
Author(s):  
T Suzuki ◽  
Y Oishi ◽  
Y Murai ◽  
Y Tasaka ◽  
Y Takeda
Keyword(s):  
Circular Cylinder ◽  
Wake Structure
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