scholarly journals Strouhal–Reynolds number relationship for flow past a circular cylinder

2017 ◽  
Vol 832 ◽  
pp. 170-188 ◽  
Author(s):  
Hongyi Jiang ◽  
Liang Cheng
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Three Dimensional ◽  
Wake Flow ◽  
Pure Mode ◽  
Laminar Regime ◽  
3D Flow ◽  
Flow Past ◽  
3D Flows ◽  
Mode A

The Strouhal–Reynolds number ($St{-}Re$) relationship for flow past a circular cylinder in the low $Re$ range of $Re\leqslant 1000$ is investigated through two- (2D) and three-dimensional (3D) direct numerical simulations (DNS). An improved method is proposed for the determination of the separating velocity and the wake width to allow for a better estimation of the wake Strouhal number $St^{\ast }$. For $Re$ in the extended laminar regime calculated by 2D DNS, the $St^{\ast }$ values are found to be more uniform than the original $St$ for the 2D flow. It is also found that the $St^{\ast }$ values for the 2D and 3D flows agree well in the laminar regime of $Re$ up to approximately 270. In addition, uniform $St^{\ast }$ values are also obtained for different mode A and mode B flow structures triggered artificially by using different cylinder span lengths in DNS. It is demonstrated that the drop in $St$ (with respect to its 2D counterpart) with the development of different 3D wake structures is due to the decrease in the separating velocity and the increase in the wake width for a 3D flow, rather than the existence of a particular wake structure such as pure mode A or vortex dislocation. However, as the wake flow becomes increasingly turbulent with further increase in $Re$, the $St^{\ast }$ value for the 3D flow increases gradually and deviates from its 2D counterpart, since for turbulent 3D flows the vortex shedding frequency scales on a length smaller than the wake width.

Numerical investigation of wake flow regimes behind a high-speed rotating circular cylinder in steady flow

2019 ◽  
Vol 878 ◽  
pp. 875-906
Author(s):  
Adnan Munir ◽  
Ming Zhao ◽  
Helen Wu ◽  
Lin Lu
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Rotation Rate ◽  
High Speed ◽  
Three Dimensional ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Rotating Circular Cylinder

Flow around a high-speed rotating circular cylinder for $Re\leqslant 500$ is investigated numerically. The Reynolds number is defined as $UD/\unicode[STIX]{x1D708}$ with $U$, $D$ and $\unicode[STIX]{x1D708}$ being the free-stream flow velocity, the diameter of the cylinder and the kinematic viscosity of the fluid, respectively. The aim of this study is to investigate the effect of a high rotation rate on the wake flow for a range of Reynolds numbers. Simulations are performed for Reynolds numbers of 100, 150, 200, 250 and 500 and a wide range of rotation rates from 1.6 to 6 with an increment of 0.2. Rotation rate is the ratio of the rotational speed of the cylinder surface to the incoming fluid velocity. A systematic study is performed to investigate the effect of rotation rate on the flow transition to different flow regimes. It is found that there is a transition from a two-dimensional vortex shedding mode to no vortex shedding mode when the rotation rate is increased beyond a critical value for Reynolds numbers between 100 and 200. Further increase in rotation rate results in a transition to three-dimensional flow which is characterized by the presence of finger-shaped (FV) vortices that elongate in the wake of the cylinder and very weak ring-shaped vortices (RV) that wrap the surface of the cylinder. The no vortex shedding mode is not observed at Reynolds numbers greater than or equal to 250 since the flow remains three-dimensional. As the rotation rate is increased further, the occurrence frequency and size of the ring-shaped vortices increases and the flow is dominated by RVs. The RVs become bigger in size and the flow becomes chaotic with increasing rotation rate. A detailed analysis of the flow structures shows that the vortices always exist in pairs and the strength of separated shear layers increases with the increase of rotation rate. A map of flow regimes on a plane of Reynolds number and rotation rate is presented.

scholarly journals Stereo MicroPIV measurements in an irrigation nozzle

2019 ◽  
Vol 85 ◽  
pp. 05005
Author(s):  
F. Gökhan Ergin ◽  
Séverine Tomas ◽  
Claudiu Pătraşcu
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Flow Structures ◽  
Rotating Flow ◽  
3D Flow ◽  
Micro Scale ◽  
Micro Channels ◽  
3D Flows ◽  
The Impact ◽  
Sharp Corners

Irrigation nozzles often feature small serpentine-shaped channels to avoid clogging. Reduced clogging improves the lifetime of the irrigation nozzle, which reduces plastic waste and thereby reduces the impact on the environment. Clogging in micro channels is often suppressed in the presence of three- dimensional (3D) flow structures called vortices. In micro scales the initiation of such 3D microstructures is normally suppressed because of the low Reynolds number inherent to micro scale flows. Passive, zig-zag shaped irrigation nozzles have the potential to induce three- dimensional rotating flow structures around sharp corners, which enhance 3D flows in the channel and thereby reduce clogging. The aim of this study is to identify and characterize such vortices using a Stereoscopic MicroPIV system.

Low-Reynolds-number wakes of elliptical cylinders: from the circular cylinder to the normal flat plate

2014 ◽  
Vol 751 ◽  
pp. 570-600 ◽  
Author(s):  
Mark C. Thompson ◽  
Alexander Radi ◽  
Anirudh Rao ◽  
John Sheridan ◽  
Kerry Hourigan
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Flat Plate ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Near Wake ◽  
Aspect Ratios ◽  
Von Karman ◽  
Von Kármán ◽  
Mode A

AbstractWhile the wake of a circular cylinder and, to a lesser extent, the normal flat plate have been studied in considerable detail, the wakes of elliptic cylinders have not received similar attention. However, the wakes from the first two bodies have considerably different characteristics, in terms of three-dimensional transition modes, and near- and far-wake structure. This paper focuses on elliptic cylinders, which span these two disparate cases. The Strouhal number and drag coefficient variations with Reynolds number are documented for the two-dimensional shedding regime. There are considerable differences from the standard circular cylinder curve. The different three-dimensional transition modes are also examined using Floquet stability analysis based on computed two-dimensional periodic base flows. As the cylinder aspect ratio (major to minor axis) is decreased, mode A is no longer unstable for aspect ratios below 0.25, as the wake deviates further from the standard Bénard–von Kármán state. For still smaller aspect ratios, another three-dimensional quasi-periodic mode becomes unstable, leading to a different transition scenario. Interestingly, for the 0.25 aspect ratio case, mode A restabilises above a Reynolds number of approximately 125, allowing the wake to return to a two-dimensional state, at least in the near wake. For the flat plate, three-dimensional simulations show that the shift in the Strouhal number from the two-dimensional value is gradual with Reynolds number, unlike the situation for the circular cylinder wake once mode A shedding develops. Dynamic mode decomposition is used to characterise the spatially evolving character of the wake as it undergoes transition from the primary Bénard–von Kármán-like near wake into a two-layered wake, through to a secondary Bénard–von Kármán-like wake further downstream, which in turn develops an even longer wavelength unsteadiness. It is also used to examine the differences in the two- and three-dimensional near-wake state, showing the increasing distortion of the two-dimensional rollers as the Reynolds number is increased.

scholarly journals Three-dimensional Floquet stability analysis of the wake of a circular cylinder

1996 ◽  
Vol 322 ◽  
pp. 215-241 ◽  
Author(s):  
Dwight Barkley ◽  
Ronald D. Henderson
Keyword(s):  
Reynolds Number ◽  
Stability Analysis ◽  
Circular Cylinder ◽  
Critical Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Neutral Stability ◽  
Two Dimensional ◽  
Numerical Stability Analysis ◽  
Mode A

Results are reported from a highly accurate, global numerical stability analysis of the periodic wake of a circular cylinder for Reynolds numbers between 140 and 300. The analysis shows that the two-dimensional wake becomes (absolutely) linearly unstable to three-dimensional perturbations at a critical Reynolds number of 188.5±1.0. The critical spanwise wavelength is 3.96 ± 0.02 diameters and the critical Floquet mode corresponds to a ‘Mode A’ instability. At Reynolds number 259 the two-dimensional wake becomes linearly unstable to a second branch of modes with wavelength 0.822 diameters at onset. Stability spectra and corresponding neutral stability curves are presented for Reynolds numbers up to 300.

Flow Past a Circular Cylinder: A Comparison Between RANS and Hybrid Turbulence Models for a Low Reynolds Number

2015 ◽  
Author(s):  
Filipe S. Pereira ◽  
Guilherme Vaz ◽  
Luís Eça
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Substantial Improvement ◽  
Computational Domain ◽  
Numerical Predictions ◽  
Flow Past ◽  
Rans Models ◽  
Domain Width

Several offshore applications deal with highly unsteady and detached flows, dominated by three dimensional effects. On such conditions, the usage of scale-resolving simulation (SRS) turbulence models has increased due to the well-known limitations of common RANS models. However, some of these offshore applications, such as flows past cylinders or raisers, present highly complex non-turbulent phenomena which, if not properly resolved, may pollute the outcome of any turbulence model. Therefore, it is crucial to mimic the flow conditions of the problem, the physical settings, and fulfil the numerical requirements of such problems to obtain reliable and accurate predictions. This paper assesses RANS and hybrid turbulence models, focusing on the dependence of the numerical predictions on the physical settings. To this end, the flow past a circular cylinder at a Reynolds number of 3900 is simulated using RANS, DDES and XLES models. The obtained results reveal a large dependence on the grid spatial resolution and physical settings, in particular on the computational domain width and boundary conditions. A substantial improvement of RANS predictions is found when a 3D computational domain is used. As expected, the hybrid models, DDES and XLES, lead to a better agreement with the experiments.

scholarly journals Three-dimensional direct numerical simulation of wake transitions of a circular cylinder

2016 ◽  
Vol 801 ◽  
pp. 353-391 ◽  
Author(s):  
Hongyi Jiang ◽  
Liang Cheng ◽  
Scott Draper ◽  
Hongwei An ◽  
Feifei Tong
Keyword(s):  
Circular Cylinder ◽  
Large Scale ◽  
Three Dimensional ◽  
Transition Process ◽  
Pure Mode ◽  
Transition Range ◽  
Continuous Increase ◽  
Probability Of Occurrence ◽  
Layer Region ◽  
Mode A

This paper presents three-dimensional (3D) direct numerical simulations (DNS) of flow past a circular cylinder over a range of Reynolds number ($Re$) up to 300. The gradual wake transition process from mode A* (i.e. mode A with large-scale vortex dislocations) to mode B is well captured over a range of $Re$ from 230 to 260. The mode swapping process is investigated in detail with the aid of numerical flow visualization. It is found that the mode B structures in the transition process are developed based on the streamwise vortices of mode A or A* which destabilize the braid shear layer region. For each case within the transition range, the transient mode swapping process consists of dislocation and non-dislocation cycles. With the increase of $Re$, it becomes more difficult to trigger dislocations from the pure mode A structure and form a dislocation cycle, and each dislocation stage becomes shorter in duration, resulting in a continuous decrease in the probability of occurrence of mode A* and a continuous increase in the probability of occurrence of mode B. The occurrence of mode A* results in a relatively strong flow three-dimensionality. A critical condition is confirmed at approximately $Re=265{-}270$, where the weakest flow three-dimensionality is observed, marking a transition from the disappearance of mode A* to the emergence of increasingly disordered mode B structures.

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.

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