Effect of a Vibrating Upstream Cylinder on a Stationary Downstream Cylinder

1986 ◽  
Vol 108 (2) ◽  
pp. 180-184 ◽  
Author(s):  
M. Moriya ◽  
H. Sakamoto
Keyword(s):  
Reynolds Number ◽  
Transverse Vibration ◽  
Flow Patterns ◽  
Uniform Flow ◽  
Circular Cylinders ◽  
Tandem Arrangement ◽  
Cylinder Diameter ◽  
Spacing Ratio ◽  
Lock In

The flow around two circular cylinders in tandem arrangement in uniform flow where the upstream cylinder is forcibly vibrated in direction normal to the approach flow was experimentally studied at Reynolds number of 6.54 × 104. The spacing ratio 1/d (1: distance between centers of cylinders, d: diameter of circular cylinders) and the ratio of amplitude to cylinder diameter a/d (a: amplitude of transverse vibration of cylinder) were varied from 2 to 6 and 0 to 0.029 respectively. The effects of the vibration of the upstream cylinder on the downstream cylinder were discussed. In particular, two distinct “lock-in” regions were observed when the upstream cylinder was vibrated with a spacing ratio of 1/d = 3.0. The cylinder vibration was so effective even for a/d as small as 0.017 to cause two different flow patterns.

VORTEX INTERFERENCE IN THE WAKE OF TWO TANDEM CIRCULAR CYLINDERS IN A CROSS FLOW

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1595-1598 ◽  
Author(s):  
KAZUO OHMI ◽  
SUXIA LI ◽  
SEUNGHEE JEON ◽  
LINGYUN CHEN
Keyword(s):  
Reynolds Number ◽  
Image Analysis ◽  
Cross Correlation ◽  
Laser Sheet ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Water Tank ◽  
Cylinder Wake ◽  
Flow Reynolds Number ◽  
Spacing Ratio

The wake of two circular cylinders in tandem arrangement is investigated by flow visualization and PIV experiments in a towing water tank. The two cylinders are spaced at L/d (spacing ratio) = 2.0 to 15.0 and the cross flow Reynolds number ranges from 60 to 120. The flow is seeded with fine Rilsan particles and illuminated by a 2 mm thick laser sheet. The PIV image analysis is done by a standard cross correlation scheme with a powerful validation algorithm followed by multi-pass adaptive cross correlation iterations. The main objective of the study is to investigate the characteristics of the downstream cylinder wake changing considerably with the spacing ratio of the two cylinders.

Effects of Cylinder Diameters, Reynolds Number and Distance Between Two-Tandem Cylinders on the Wake Profile and Turbulence Intensity

2011 ◽  
Author(s):  
Amin Rahimzadeh ◽  
Majid Malek Jafarian ◽  
Amir Khoshnevis
Keyword(s):  
Reynolds Number ◽  
Velocity Profile ◽  
Turbulence Intensity ◽  
Stream Velocity ◽  
Hot Wire ◽  
Velocity Defect ◽  
One Dimensional ◽  
Tandem Cylinders ◽  
Cylinder Diameter ◽  
Spacing Ratio

A series of experimental and numerical investigations on two tandem cylinders wake have been studied. The velocity profile and turbulence intensity have been acquired by a single one dimensional Hot Wire anemometer. The two cylinders were mounted in a tandem manner in the horizontal mid plane of the working section. The effect of the upstream cylinder diameter, Reynolds number and the distance between the cylinders on the wake profile and turbulence intensity on the downstream cylinder was investigated, while the Reynolds number ranged between 1.5× ⟦10⟧ ^4 ∼ 3× ⟦10⟧ ^4. The upstream cylinder diameter (d) was 10, 20 and 25 mm, while the downstream cylinder diameter (D) was 25 mm, corresponding to d/D ranging from 0.4 ∼1.0. The spacing ratio L/d (where L is the distance between the upstream cylinder center and the leading stagnation point of the downstream cylinder) was 2 and 5.5, covering different flow regimes. Observations indicate that two symmetric turbulence intensity peak will occur at mean velocity gradient area. Turbulence area will increase in width for both L/d = 2 and 5.5 as increasing distance from the cylinder (x/D) and decreasing free stream velocity. But totally the range of the turbulence area for L/d = 5.5 is greater than L/d = 2. The wake profiles show that the velocity defect increases as increasing upstream cylinder’s diameter for L/d = 5.5. While this order cannot be accessed for L/d = 2. It is observed that sudden and unusual velocity defect happened for L/d = 2 and d/D = 0.8 cases, which means that the most velocity defect is running on. Also, numerical solution results of velocity profile have been compared with the mentioned experimental results at station 4 and velocity of 10 m/s for both L/d = 2 and 5.5. Results shows a little difference because of using one-dimensional Hot-wire.

Phase-Lag-Induced Fluctuating Lift Forces on Two Tandem Bluff Bodies

2015 ◽  
Author(s):  
Md. Mahbub Alam ◽  
Ma Zhe
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Vortex Dynamics ◽  
Lift Coefficient ◽  
Nonlinear Function ◽  
Local Maximum ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Phase Lag ◽  
Spacing Ratio

A numerical simulation at a Reynolds number Re = 200 is conducted to find how flow-induced forces on two tandem circular cylinders is connected to the phase lag between vortex sheddings from the cylinders. The spacing ratio L* (= L/D) is varied from 2 to 9, where L is the cylinder center-to-center spacing and D is the cylinder diameter. Here we mainly focus on fluctuating lift coefficient CLf of the upstream cylinder, vortex dynamics in the gap between cylinders, and phase lag ϕ between the vortex sheddings from the two cylinders for L* larger than the critical where the co-shedding flow prevails. ϕ is indeed nonlinear function of L*, Strouhal number (St) and convection velocity of vortices in the gap between the cylinders. We unearth that the upstream cylinder CLf is affected by both L* and ϕ. While the contribution of L* to CLf diminishes rapidly with L*, that of ϕ makes the L*-dependent CLf variation damped-sinusoidal, persisting in the L* range examined. The inphase and antiphase flows respectively correspond to a local maximum and minimum CLf. How CLf is correlated with L* and ϕ can be deduced as, C L f = A e −α L * + B e −β L * sin ϕ + π 2 + C , where A, α, B, β and C are constants. The physics behind the damped-sinusoidal variation in CLf is discussed.

Vorticity Shedding and Acoustic Resonance Excitation of Two Tandem Spirally Finned Cylinders in Cross-Flow

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Root Diameter ◽  
Circular Cylinders ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Spacing Ratio

Abstract The aeroacoustic response of two tandem spirally finned cylinders is experimentally investigated. Three different pairs of finned cylinders are studied with fin pitch-to-root diameter ratios (p/Dr) ranging between 0.37≤p/Dr≤0.74. The spiral fins are crimped similar to those used in industrial heat exchangers. The results of the finned cylinders are compared with bare, circular cylinders with a modified equivalent diameter (Deq). The spacing ratio (L/Deq) between the cylinders are kept constant at L/Deq=2.00. The Strouhal number (StDeq) of the tandem finned cylinders is found to be higher compared to the tandem bare cylinders, resulting in an earlier onset of coincidence resonance. Moreover, unlike the tandem bare cylinders, the Strouhal number of the finned cylinders did not depend on the Reynolds number, suggesting that the flow characteristics around the finned cylinders are unaffected by Reynolds number. Only the tandem finned cylinders with the lowest fin pitch-to-root diameter ratio (p/Dr=0.37) were capable of exciting precoincidence acoustic resonance. The precoincidence resonance mechanism is similar to that observed in in-line tube bundles.

Phase jump and energy transfer of forced oscillating circular cylinder in uniform flow

2016 ◽  
Vol 231 (2) ◽  
pp. 496-510
Author(s):  
Guoqiang Tang ◽  
Lin Lu ◽  
Ming Zhao ◽  
Mingming Liu ◽  
Zhi Zong
Keyword(s):  
Reynolds Number ◽  
Energy Transfer ◽  
Circular Cylinder ◽  
Phase Difference ◽  
Uniform Flow ◽  
Phase Jump ◽  
Fluid Forces ◽  
Special Cases ◽  
Lock In ◽  
Transfer Direction

The phase jump, energy transfer, and the associated vortex shedding modes of a circular cylinder undergoing forced oscillation normal to the incoming uniform flow are investigated numerically at Reynolds number ( Re) of 200. The dependence of the fluid forces on the non-dimensional oscillating amplitude A* =  A/ D ∈ [0.1, 0.6] and frequency f* =  fe/ fs ∈ [0.5, 2.0] is examined, where A is the oscillating amplitude, D is the cylinder diameter, fe is the cylinder oscillating frequency, and fs is the Strouhal frequency of fixed cylinder at the same Reynolds number, respectively. The lock-in region is identified by the combination of Fourier analysis and Lissajous phase diagram. The phase difference between displacement and lift fluctuation and the energy transfer between fluid and structure are discussed. Within the lock-in region, a jump in the phase difference is found to occur in the cases with A* = 0.5 and 0.55 without a wake mode transition. The numerical results reveal that the appearance of the phase jump is consistent with the reversal of the energy transfer direction. For the special cases of A* = 0.5 and 0.55, changes in the sign of energy transfer are observed, while no reversal of energy transfer is observed at other amplitudes. The energy transfer direction is either from fluid to cylinder when A* ∈ [0.1, 0.4] or from cylinder to fluid when A* ≥ 0.6. It is confirmed that the energy transfer between fluid and cylinder is not only dependent on cylinder oscillating frequency but also on cylinder oscillating amplitude.

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