First instability and structural sensitivity of the flow past two side-by-side cylinders

2014 ◽  
Vol 749 ◽  
pp. 627-648 ◽  
Author(s):  
M. Carini ◽  
F. Giannetti ◽  
F. Auteri
Keyword(s):  
Bluff Body ◽  
Passive Control ◽  
Base Flow ◽  
Circular Cylinders ◽  
A Posteriori ◽  
Instability Mechanism ◽  
Structural Sensitivity ◽  
Flow Past ◽  
Structural Sensitivity Analysis ◽  
Gap Spacing

AbstractThe onset of two-dimensional instabilities in the flow past two side-by-side circular cylinders is numerically investigated in the ranges $0.1\leq g\leq 3$ and $\mathit{Re}<100$, with $g$ being the non-dimensional gap spacing between the surfaces of the two cylinders and $\mathit{Re}$ the Reynolds number. A comprehensive, global stability analysis of the symmetric base flow is carried out, indicating that three harmonic modes and one steady antisymmetric mode become unstable at different values of $g$ and $\mathit{Re}$. These modes are known to promote distinct flow regimes at increasing values of $g$: single bluff-body, asymmetric, in-phase and antiphase synchronized vortex shedding. For each mode, the inherent structural sensitivity is examined in order to identify the core region of the related instability mechanism. In addition, by exploiting the structural sensitivity analysis to base flow modifications, a passive control strategy is proposed for the simultaneous suppression of the two synchronized shedding modes using two small secondary cylinders. Its effectiveness is then validated a posteriori by means of direct numerical simulations.

Instability and sensitivity of the flow around a rotating circular cylinder

2010 ◽  
Vol 650 ◽  
pp. 513-536 ◽  
Author(s):  
JAN O. PRALITS ◽  
LUCA BRANDT ◽  
FLAVIO GIANNETTI
Keyword(s):  
Circular Cylinder ◽  
Passive Control ◽  
Base Flow ◽  
Structural Sensitivity ◽  
Rotation Rates ◽  
Rotating Circular Cylinder ◽  
Flow Stagnation ◽  
Two Dimensional Flow ◽  
Classic Approach ◽  
Structural Sensitivity Analysis

The two-dimensional flow around a rotating circular cylinder is studied at Re = 100. The instability mechanisms for the first and second shedding modes are analysed. The region in the flow with a role of ‘wavemaker’ in the excitation of the global instability is identified by considering the structural sensitivity of the unstable mode. This approach is compared with the analysis of the perturbation kinetic energy production, a classic approach in linear stability analysis. Multiple steady-state solutions are found at high rotation rates, explaining the quenching of the second shedding mode. Turning points in phase space are associated with the movement of the flow stagnation point. In addition, a method to examine which structural variation of the base flow has the largest impact on the instability features is proposed. This has relevant implications for the passive control of instabilities. Finally, numerical simulations of the flow are performed to verify that the structural sensitivity analysis is able to provide correct indications on where to position passive control devices, e.g. small obstacles, in order to suppress the shedding modes.

Induced Separation and Vorticity Using Roughness in VIV of Circular Cylinders at 8×103 < Re < 2.0×105

2008 ◽  
Author(s):  
Michael M. Bernitsas ◽  
Kamaldev Raghavan ◽  
G. Duchene
Keyword(s):  
Surface Roughness ◽  
Experimental Investigation ◽  
Fluid Flow ◽  
Circular Cylinder ◽  
Passive Control ◽  
Flow Characteristics ◽  
Grit Size ◽  
Strip Width ◽  
Circular Cylinders ◽  
Flow Past

Results of an experimental investigation on fluid flow past an elastically mounted circular cylinder with rectangular surface roughness strips are presented. Flow characteristics change depending on the strip width, roughness grit size, and location. Roughness size and distribution can be designed to enhance or reduce/suppress VIV amplitude and increase or reduce the range of synchronization, respectively. To the authors’ knowledge this is the first study in passive control of VIV using properly distributed roughness.

Numerical Study of Drag Reduction for Flow Past a Square Cylinder Through Passive Control Method at Various Gap Spacing

2017 ◽  
Vol 14 (12) ◽  
pp. 5872-5881
Author(s):  
Shams-ul-Islam ◽  
Raheela Manzoor ◽  
Tahira Mengal ◽  
Asma Naeem ◽  
Sajida Parveen ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Passive Control ◽  
Control Method ◽  
Numerical Study ◽  
Square Cylinder ◽  
Flow Past ◽  
Gap Spacing

On the origin of the flip–flop instability of two side-by-side cylinder wakes

2014 ◽  
Vol 742 ◽  
pp. 552-576 ◽  
Author(s):  
M. Carini ◽  
F. Giannetti ◽  
F. Auteri
Keyword(s):  
Low Frequency ◽  
Neutral Curve ◽  
Base Flow ◽  
Circular Cylinders ◽  
Complex Conjugate ◽  
Flip Flop ◽  
Gap Flow ◽  
Two Dimensional Flow ◽  
Gap Spacing ◽  
Cylinder Wakes

AbstractIn this work the flip–flop instability occurring in the flow past two side-by-side circular cylinders is numerically investigated within the range of non-dimensional gap spacing $0.6<g<1.4$ and Reynolds number $50<Re\leq 90$. The inherent two-dimensional flow pattern is characterized by an asymmetric unsteady wake (with respect to the horizontal axis of symmetry) with the gap flow being deflected alternatively toward one of the cylinders. Such behaviour has been ascribed by other authors to a bistability of the flow, and therefore termed flip–flop. In contrast, the simulations performed herein provide new evidence that at low Reynolds numbers the flip–flopping state develops through an instability of the in-phase synchronized vortex shedding between the two cylinder wakes. This new scenario is confirmed and explained by means of a linear global stability investigation of the in-phase periodic base flow. The Floquet analysis reveals indeed that a pair of complex-conjugate multipliers becomes unstable having the same low frequency as the gap flow flip-over. The neutral curve of this secondary instability is tracked within the above range of gap spacing. The spatiotemporal shape of the unstable Floquet mode is then analysed and its structural sensitivity is considered in order to identify the ‘core’ region of the flip–flop instability mechanism.

Study on Magnetohydrodynamic Flow Past Two Circular Cylinders in Staggered Arrangement

CFD Letters ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 65-77
Author(s):  
Nur Marissa Kamarul Baharin ◽  
Mohd Azan Mohammed Sapardi ◽  
Nur Nadhirah Ab Razak ◽  
Ahmad Hussein Abdul Hamid ◽  
Syed Noh Syed Abu Bakar
Keyword(s):  
Heat Transfer ◽  
Bluff Body ◽  
Stokes Equations ◽  
Mhd Flow ◽  
Clean Energy ◽  
Magnetohydrodynamic Flow ◽  
Circular Cylinders ◽  
Heated Wall ◽  
Flow Past ◽  
Staggered Arrangement

The fusion reactor is anticipated to be a new source of clean energy. Magnetohydrodynamic flow in the fusion blanket is expected to cause the flow to be highly stable, causing the heat transfer to be poor. Passive vortex promoter such as bluff body is one of the methods found to be has a great potential in optimizing the heat transfer. In this study, two circular cylinders in a staggered arrangement are introduced to promote vortices to enhance heat convection from a heated wall using an electrically conducting fluid under a constant magnetic field. The effect of the Hartmann friction parameter and the height differential onto the Nusselt number were examined. Modified Navier—Stokes equations known as SM82 were used using OpenFOAM to simulate the confined, quasi-two-dimensional, incompressible and laminar MHD flow past the bluff bodies. It was found that the heat transfer is better when the height differential is small.

The supersonic and low-speed flows past circular cylinders of finite length supported at one end

1962 ◽  
Vol 12 (3) ◽  
pp. 367-387 ◽  
Author(s):  
D. M. Sykes
Keyword(s):  
Mach Number ◽  
Finite Length ◽  
Central Region ◽  
Diameter Ratio ◽  
Circular Cylinders ◽  
Form Drag ◽  
Drag Coefficients ◽  
Low Speed ◽  
Flow Past ◽  
Length To Diameter Ratio

The flow past circular cylinders of finite length, supported at one end and lying with their axes perpendicular to a uniform stream, has been investigated in a supersonic stream at Mach number 1.96 and also in a low-speed stream. In both stream it was found that the flow past the cylinders could be divided into three regions: (a) a central region, (b) that near the free end of the cylinder, and (c) that near the supported end. The locations of the second and third regions were found to be almost independent of the cylinder length-to-diameter ratio, provided that this exceeded 4, while the flow within and the extent of the first region were dependent on this ratio. Form-drag coefficients determined in the central region in the supersonic flow were in close agreement with the values determined at the same Mach number by other workers. In the low-speed flow the local form-drag coefficients were dependent on length-to-diameter ratio and were always less than that of an infinite-length cylinder at the same Reynolds number.

Steady approach of unsteady low-Reynolds-number flow past two rotating circular cylinders

2013 ◽  
Vol 736 ◽  
pp. 414-443 ◽  
Author(s):  
Y. Ueda ◽  
T. Kida ◽  
M. Iguchi
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Stokes Equations ◽  
Low Reynolds Number ◽  
Vortex Method ◽  
The Self ◽  
Circular Cylinders ◽  
Far Field ◽  
Flow Past ◽  
Low Reynolds

AbstractThe long-time viscous flow about two identical rotating circular cylinders in a side-by-side arrangement is investigated using an adaptive numerical scheme based on the vortex method. The Stokes solution of the steady flow about the two-cylinder cluster produces a uniform stream in the far field, which is the so-called Jeffery’s paradox. The present work first addresses the validation of the vortex method for a low-Reynolds-number computation. The unsteady flow past an abruptly started purely rotating circular cylinder is therefore computed and compared with an exact solution to the Navier–Stokes equations. The steady state is then found to be obtained for $t\gg 1$ with ${\mathit{Re}}_{\omega } {r}^{2} \ll t$, where the characteristic length and velocity are respectively normalized with the radius ${a}_{1} $ of the circular cylinder and the circumferential velocity ${\Omega }_{1} {a}_{1} $. Then, the influence of the Reynolds number ${\mathit{Re}}_{\omega } = { a}_{1}^{2} {\Omega }_{1} / \nu $ about the two-cylinder cluster is investigated in the range $0. 125\leqslant {\mathit{Re}}_{\omega } \leqslant 40$. The convection influence forms a pair of circulations (called self-induced closed streamlines) ahead of the cylinders to alter the symmetry of the streamline whereas the low-Reynolds-number computation (${\mathit{Re}}_{\omega } = 0. 125$) reaches the steady regime in a proper inner domain. The self-induced closed streamline is formed at far field due to the boundary condition being zero at infinity. When the two-cylinder cluster is immersed in a uniform flow, which is equivalent to Jeffery’s solution, the streamline behaves like excellent Jeffery’s flow at ${\mathit{Re}}_{\omega } = 1. 25$ (although the drag force is almost zero). On the other hand, the influence of the gap spacing between the cylinders is also investigated and it is shown that there are two kinds of flow regimes including Jeffery’s flow. At a proper distance from the cylinders, the self-induced far-field velocity, which is almost equivalent to Jeffery’s solution, is successfully observed in a two-cylinder arrangement.

Three-dimensional flow past two stationary side-by-side circular cylinders

2022 ◽  
Vol 244 ◽  
pp. 110379
Author(s):  
Weilin Chen ◽  
Chunning Ji ◽  
Md. Mahbub Alam ◽  
Yuhao Yan
Keyword(s):  
Three Dimensional ◽  
Circular Cylinders ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Past
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