scholarly journals Control of vortex shedding around a circular cylinder using bubble tabs in the laminar flow regime

2021 ◽  
Vol 39 (4) ◽  
pp. 1108-1116
Author(s):  
E.O. Atofarati ◽  
A.O. Muritala ◽  
B.O. Malomo ◽  
S.A. Adio
Keyword(s):  
Circular Cylinder ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
Flow Analysis ◽  
Small Diameter ◽  
Ansys Fluent ◽  
Spacing Ratio ◽  
Flow Domain ◽  
Drag And Lift ◽  
Fatigue Failures

Vortex induced vibration (VIV) is the major cause of several catastrophic disasters due to fatigue failures induced by drag and lift forces in aerodynamic systems. This study investigates the control of VIV phenomenon through passive bubble tab(s) having a small diameter (d) relative to the main circular cylinder (D) in a two-dimensional (2-D) flow domain. Using ANSYS Fluent computational software, flow analysis was conducted at a Reynolds number (Re) of 80 for various bubble tab configurations at different spacing ratios (x/D) and diameter ratios (d/D). The drag coefficient, the velocity and pressure contours, along with the flow streamlines in eachcase were studied. The results indicated the optimized tab(s) positions for different spacing ratios, diameter ratios, and  configurations. The study effectively established that passive bubble tabs can potentially control VIV associated with flows around a circular cylinder. Keywords: Vortex Shedding; Drag Coefficient; Circular Cylinder; Bubble Tab(S); Spacing Ratio; Diameter Ratio.

scholarly journals Effect of Cylinder Gap Ratio on The Wake of a Circular Cylinder Enclosed by Various Perforated Shrouds

CFD letters ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 51-68
Author(s):  
Nurul Azihan Ramli ◽  
Azlin Mohd Azmi ◽  
Ahmad Hussein Abdul Hamid ◽  
Zainal Abidin Kamarul Baharin ◽  
Tongming Zhou
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Control Method ◽  
Lift Coefficient ◽  
Base Case ◽  
Bluff Bodies ◽  
Ansys Fluent ◽  
Gap Ratio ◽  
Spacing Ratio

Flow over bluff bodies produces vortex shedding in their wake regions, leading to structural failure from the flow-induced forces. In this study, a passive flow control method was explored to suppress the vortex shedding from a circular cylinder that causes many problems in engineering applications. Perforated shrouds were used to control the vortex shedding of a circular cylinder at Reynolds number, Re = 200. The shrouds were of non-uniform and uniform holes with 67% porosity. The spacing gap ratio between the shroud and the cylinder was set at 1.2, 1.5, 2, and 2.2. The analysis was conducted using ANSYS Fluent using a viscous laminar model. The outcomes of the simulation of the base case were validated with existing studies. The drag coefficient, Cd, lift coefficient, Cl and the Strouhal number, St, as well as vorticity contours, velocity contours, and pressure contours were examined. Vortex shedding behind the shrouded cylinders was observed to be suppressed and delayed farther downstream with increasing gap ratio. The effect was significant for spacing ratio greater than 2.0. The effect of hole types: uniform and non-uniform holes, was also effective at these spacing ratios for the chosen Reynolds number of 200. Specifically, a spacing ratio of 1.2 enhanced further the vortex intensity and should be avoided.

Laminar Forced Convection From a Circular Cylinder Placed in a Micropolar Fluid

2006 ◽  
Vol 129 (3) ◽  
pp. 256-264 ◽  
Author(s):  
F. M. Mahfouz
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Prandtl Number ◽  
Drag Coefficient ◽  
Forced Convection ◽  
Vortex Shedding ◽  
Micropolar Fluid ◽  
Clear Trend ◽  
Thermal Fields ◽  
Laminar Forced Convection

In this paper laminar forced convection associated with the cross-flow of micropolar fluid over a horizontal heated circular cylinder is investigated. The conservation equations of mass, linear momentum, angular momentum and energy are solved to give the details of flow and thermal fields. The flow and thermal fields are mainly influenced by Reynolds number, Prandtl number and material parameters of micropolar fluid. The Reynolds number is considered up to 200 while the Prandtl number is fixed at 0.7. The dimensionless vortex viscosity is the only material parameter considered in this study and is selected in the range from 0 to 5. The study has shown that generally the mean heat transfer decreases as the vortex viscosity increases. The results have also shown that both the natural frequency of vortex shedding and the amplitude of oscillating lift force experience clear reduction as the vortex viscosity increases. Moreover, the study showed that there is a threshold value for vortex viscosity above which the flow over the cylinder never responds to perturbation and stays symmetric without vortex shedding. Regarding drag coefficient, the results have revealed that within the selected range of controlling parameters the drag coefficient does not show a clear trend as the vortex viscosity increases.

scholarly journals Numerical Simulation of Flow Control around a Circular Cylinder by Installing a Wedge-Shaped Device Upstream

2019 ◽  
Vol 7 (12) ◽  
pp. 422 ◽  
Author(s):  
Xiaoshuang Han ◽  
Jie Wang ◽  
Bo Zhou ◽  
Guiyong Zhang ◽  
Soon-Keat Tan
Keyword(s):  
Circular Cylinder ◽  
Cavity Mode ◽  
Wake Flow ◽  
Side Length ◽  
Length Ratio ◽  
Drag And Lift Coefficients ◽  
Spacing Ratio ◽  
Wake Patterns ◽  
Drag And Lift ◽  
Sudden Jump

The effect of a triangular wedge upstream of a circular cylinder has been investigated, and the findings are presented herein. The triangular wedge is equilateral in plan form, and the Reynolds number based on the diameter of the main cylinder is approximately 200. Contours of vorticity clearly show that two entirely different wake patterns exist between the wedge and the main cylinder. There also exists a critical spacing ratio and side length ratio at which the wake flow pattern shifts from one within the cavity mode to one within the wake impingement mode. For a relatively small side length ratio of l w / D = 0.20 and 0.27, where the side length refers to the length of one side of the triangular wedge, the drag and lift coefficients decrease monotonically with the spacing ratio. There is a sudden jump of the drag and lift coefficients at larger side length ratios of l w / D = 0.33 and 0.40. This study shows that at a spacing ratio of L/D = 2.8 (where L is the distance between the vertex of the wedge and the center of the cylinder) and a wedge side length of l w / D = 0.40, the reduction of the amplitude of lift and mean drag coefficient on the main cylinder are 71.9% and 60.1%, respectively.

The effect of buoyancy on vortex shedding in the near wake of a circular cylinder

1990 ◽  
Vol 220 ◽  
pp. 253-266 ◽  
Author(s):  
Keun-Shik Chang ◽  
Jong-Youb Sa
Keyword(s):  
Nusselt Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Transport Equation ◽  
Fourth Order ◽  
Vortex Shedding ◽  
Near Wake ◽  
Periodic Flows ◽  
Vortex Pattern ◽  
Vorticity Transport

The phenomenon of vortex shedding from a heated/cooled circular cylinder has been investigated numerically in the mixed natural and forced convection regimes. Accuracy of the computation was achieved by the fourth-order Hermitian relation applied to the contravariant velocity components in the convection terms of the vorticity transport equation, and by the far-boundary stream-function condition of an integral-series form developed by the authors. Purely periodic flows at Re = 100, efficiently established through the use of a direct elliptic solver called the SEVP, was found to degenerate into a steady twin-vortex pattern at the critical Grashof number 1500, confirming an earlier experimental observation identified as ‘breakdown of the Kármán vortex street’. Various other buoyancy effects about the heated/cooled cylinder are discussed by means of the flow patterns, the Nusselt number and the drag coefficient curves.

Viscous Flow Past a Circular Cylinder Below a Free Surface

2014 ◽  
Author(s):  
Benjamin Bouscasse ◽  
Andrea Colagrossi ◽  
Salvatore Marrone ◽  
Antonio Souto-Iglesias
Keyword(s):  
Free Surface ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Mixing Processes ◽  
Surface Evolution ◽  
Flow Past ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Karman Vortex ◽  
Drag And Lift

Flow past a circular cylinder close to a free surface at low Reynolds and large Froude numbers is investigated numerically using the Smoothed Particle Hydrodynamics model. This meshless method allows for a non-diffusive computation of the free surface evolution, even while breaking and fragmentation may occur. The distance of the cylinder to the free surface, submergence, is varied in order to investigate the detached flow patterns dependence with this factor. Vorticity shed by the cylinder, vortex generation due to free surface breaking, mixing processes, and drag and lift coefficients behavior are discussed. It has been found that, for small submergences, the classical Von Karman vortex shedding from the cylinder does not take place. In turn, moderate vortex shedding occurs, departing not from the cylinder but from vorticity generated at the free surface. This shedding takes places simultaneously with the transport of free surface fluid elements into the bulk of the fluid. It has been also found that for even smaller depth ratios, a vorticity layer remains spatially localized between the cylinder and the free surface, and a stagnation recirculating area develops behind the cylinder. Results are compared with literature finding reasonable qualitatively agreement with experimental works conducted with similar geometrical configuration but larger Reynolds number.

Interaction of a Steady Approach Flow and a Circular Cylinder Undergoing Forced Oscillation

1997 ◽  
Vol 119 (4) ◽  
pp. 808-813 ◽  
Author(s):  
Jianfeng Zhang ◽  
Charles Dalton
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Numerical Study ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Large Eddy Simulation Model ◽  
Drag And Lift Coefficients ◽  
Eddy Simulation ◽  
Drag And Lift

This paper presents a numerical study on the interaction of a steady approach flow and the forced transverse oscillation of a circular cylinder. The two-dimensional stream-function/vorticity formulation of the Navier-Stokes equations is solved by a semi-implicit finite-difference scheme. Calculations for flows with different amplitude (a) and frequency (fc) of the oscillation of the cylinder show a strong effect of the oscillation when fc is close to fso, the vortex shedding frequency, of the stationary cylinder. Lock-on of vortex shedding, distinct flow patterns, and increase in both drag and lift coefficients from those of a stationary cylinder are observed for Reynolds number Re = 200, a/R (R is the radius of the cylinder) from 1.0 to 2.0, fc/fso from 0.85 to 1.7. For Re = 855, a/R = 0.26, a large eddy simulation model for turbulent flow is used. The results at Re = 855 and a/R = 0.26 show that lock-on has occurred for fc/fso ≥ 0.85. The behavior of the drag and lift coefficients is seen to be influenced by the lock-on phenomenon.

A Numerical Investigation of the Effects of Flow Pulsations on the Drag Force Over a Cylinder

2011 ◽  
Author(s):  
Eric D’herde ◽  
Laila Guessous
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Free Stream ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

Flow over a cylinder is a fundamental fluid mechanics problem that involves a simple geometry, yet increasingly complex flow patterns as the Reynolds number is increased, most notably the development of a Karman vortex with a natural vortex shedding frequency fs when the Reynolds number exceeds a value of about 40. The goal of this ongoing study is to numerically investigate the effect of an incoming free-stream velocity pulsation with a mean Reynolds number of 100 on the drag force over and vorticity dynamics behind a circular cylinder. This paper reports on initial results involving unsteady, laminar and incompressible flows over a circular cylinder. Sinusoidal free-stream pulsations with amplitudes Av varying between 25% and 75% of the mean free-stream velocity and frequencies f varying between 0.25 and 5 times the natural shedding frequency were considered. Of particular interest to us is the interaction between the pulsating frequency and natural vortex shedding frequency and the resulting effects on drag. Interestingly, at frequencies close to the natural frequency, and to twice the natural frequency, a sudden drop in the mean value of the drag coefficient is observed. This drop in the drag coefficient is also accompanied by a change in the flow and vortex shedding patterns observed behind the cylinder.

A Numerical Investigation of the Effects of Flow Pulsations on the Vortex Shedding, Drag and Lift Forces Over a Cylinder

2011 ◽  
Author(s):  
Eric D’herde ◽  
Laila Guessous
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Free Stream ◽  
Lift Coefficient ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency ◽  
Drag And Lift

Flow over a cylinder is a fundamental fluid mechanics problem that involves a simple geometry, yet increasingly complex flow patterns as the Reynolds number is increased, most notably the development of a Karman vortex with a natural vortex shedding frequency when the Reynolds number exceeds a value of about 40. The goal of this ongoing study is to numerically investigate the effect of an incoming free-stream velocity pulsation with a mean Reynolds number of 100 on the drag and lift forces over and vorticity dynamics behind a circular cylinder. This paper reports on initial results involving unsteady, laminar and incompressible flows over a circular cylinder. Sinusoidal free-stream pulsations with amplitudes Av varying between 25% and 75% of the mean free-stream velocity and frequencies varying between 0.25 and 5 times the natural shedding frequency fs were considered. Of particular interest to us is the interaction between the pulsating frequency and natural vortex shedding frequency and the resulting effects on drag. Interestingly, at frequencies close to the natural frequency, and to twice the natural frequency, a sudden drop in the mean value of the drag coefficient is observed. The first drop in the drag coefficient, i.e. near f = fs, is also accompanied by a change in the flow and vortex shedding patterns observed behind the cylinder. This change in vortex shedding pattern manifests itself as a departure from symmetrical shedding, and in a non-zero mean lift coefficient value. The second drop, i.e. near f = 2 fs, has similar characteristics, except that the mean lift coefficient remains at zero.

scholarly journals Numerical Simulation of Drag Reduction on a Square Rod Detached with Two Control Rods at Various Gap Spacing via Lattice Boltzmann Method

Symmetry ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 475 ◽  
Author(s):  
Raheela Manzoor ◽  
Asma Khalid ◽  
Ilyas Khan ◽  
Shams-Ul-Islam ◽  
Dumitru Baleanu ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Lattice Boltzmann Method ◽  
Vortex Shedding ◽  
Lattice Boltzmann ◽  
Flow Mode ◽  
Percentage Reduction ◽  
Spacing Ratio ◽  
Boltzmann Method ◽  
Gap Spacing ◽  
Control Rods

Numerical simulations are performed to examine the effect of size of control rods (d1) and spacing ratio (g) on flow around a square rod with upstream and downstream control rods aligned in-line using the lattice Boltzmann method (LBM). The Reynolds number (Re) is fixed at Re = 160, while the spacing between the main rod and control rods is taken in the range 1 ≤ g ≤ 5 and the size of the control rod is varied between 4 and 20. Seven different types of flow mods are observed in this study at different values of g and d1. Variation in force statistics, like mean drag coefficient (Cdmean), Strouhal number (St), root mean square values of drag (Cdrms) and lift coefficients (Clrms), and percentage reduction in mean drag coefficient is discussed in detail. It was examined that vortex shedding completely suppressed at (g, d1) = (1, 12), (2, 12), and (2, 16) where steady flow mode exists. Moreover, it was found that at large gap spacing, where g = 5, the effect of control rods on the main rod vanishes. Due to this strong vortex shedding produced and as a result, maximum value of Cdmean is found at (g, d1) = (5, 8). The negative values of mean drag force are also observed at some gap spacing and size of control rods are due to the effect of thrust. Furthermore, the maximum percentage reduction in Cdmean is 121%, found at (g, d1) = (2, 20).

A PID Control of Flow Over a Circular Cylinder

2011 ◽  
Author(s):  
Donggun Son ◽  
Seung Jeon ◽  
Haecheon Choi
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Pid Control ◽  
Transverse Velocity ◽  
Cylinder Surface ◽  
Control Performance ◽  
Feedback Controls ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Drag And Lift

In the present study, we apply proportional-integral-differential (PID) feedback controls to flow over a circular cylinder for suppression of vortex shedding in the wake. The transverse velocity at a centerline location in the wake is measured and used for the feedback control. The actuation (blowing/suction) is provided to the flow at the upper and lower slots on the cylinder surface near the separation point based on the P, PI or PD control. The sensing location is varied from 1d to 4d from the center of the cylinder. Given each sensing location, the optimal proportional gain in the sense of minimizing the sensing velocity fluctuations is obtained for the P control. The P control significantly reduces the fluctuations of the sensing velocity at certain sensing positions that is called the effective sensing region. The additions of I and D controls to the P control increase the control performance and broaden the effective sensing location. The P, PI and PD controls significantly reduce the velocity fluctuations and attenuate vortex shedding in the wake, resulting in the reductions in the mean drag and lift fluctuations.

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