Suppression of vortex shedding for flow around a circular cylinder using optimal control

2001 ◽  
Vol 38 (1) ◽  
pp. 43-69 ◽  
Author(s):  
C. Homescu ◽  
I. M. Navon ◽  
Z. Li
Keyword(s):  
Optimal Control ◽  
Circular Cylinder ◽  
Vortex Shedding

scholarly journals Nonlinear optimal suppression of vortex shedding from a circular cylinder

2015 ◽  
Vol 775 ◽  
pp. 241-265 ◽  
Author(s):  
X. Mao ◽  
H. M. Blackburn ◽  
S. J. Sherwin
Keyword(s):  
Optimal Control ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Nonlinear Optimal Control ◽  
Discrete Control ◽  
Small Magnitude ◽  
Recirculation Bubble ◽  
Flow Past ◽  
Linearized Stability

This study is focused on two- and three-dimensional incompressible flow past a circular cylinder for Reynolds number $\mathit{Re}\leqslant 1000$. To gain insight into the mechanisms underlying the suppression of unsteadiness for this flow we determine the nonlinear optimal open-loop control driven by surface-normal wall transpiration. The spanwise-constant wall transpiration is allowed to oscillate in time, although steady forcing is determined to be most effective. At low levels of control cost, defined as the square integration of the control, the sensitivity of unsteadiness with respect to wall transpiration is a good approximation of the optimal control. The distribution of this sensitivity suggests that the optimal control at small magnitude is achieved by applying suction upstream of the upper and lower separation points and blowing at the trailing edge. At high levels of wall transpiration, the assumptions underlying the linearized sensitivity calculation become invalid since the base flow is eventually altered by the size of the control forcing. The large-magnitude optimal control is observed to spread downstream of the separation point and draw the shear layer separation towards the rear of the cylinder through suction, while blowing along the centreline eliminates the recirculation bubble in the wake. We further demonstrate that it is possible to completely suppress vortex shedding in two- and three-dimensional flow past a circular cylinder up to $\mathit{Re}=1000$, accompanied by 70 % drag reduction when a nonlinear optimal control of moderate magnitude (with root-mean-square value 8 % of the free-stream velocity) is applied. This is confirmed through linearized stability analysis about the steady-state solution when the nonlinear optimal wall transpiration is applied. While continuously distributed wall transpiration is not physically realizable, the study highlights localized regions where discrete control strategies could be further developed. It also highlights the appropriate range of application of linear and nonlinear optimal control to this type of flow problem.

scholarly journals Vortex Shedding from a Circular Cylinder with Spiral Fin

2008 ◽  
Vol 3 (6) ◽  
pp. 787-795 ◽  
Author(s):  
Hiromitsu HAMAKAWA ◽  
Keisuke NAKASHIMA ◽  
Tomohiro KUDO ◽  
Eiichi NISHIDA ◽  
Tohru FUKANO
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding

Vortex shedding from a circular cylinder in moderate-Reynolds-number shear flow

1980 ◽  
Vol 101 (4) ◽  
pp. 721-735 ◽  
Author(s):  
Masaru Kiya ◽  
Hisataka Tamura ◽  
Mikio Arie
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Transverse Velocity ◽  
Number Range ◽  
Uniform Shear ◽  
Reynolds Number Range ◽  
Moderate Reynolds Number ◽  
Shear Parameter

The frequency of vortex shedding from a circular cylinder in a uniform shear flow and the flow patterns around it were experimentally investigated. The Reynolds number Re, which was defined in terms of the cylinder diameter and the approaching velocity at its centre, ranged from 35 to 1500. The shear parameter, which is the transverse velocity gradient of the shear flow non-dimensionalized by the above two quantities, was varied from 0 to 0·25. The critical Reynolds number beyond which vortex shedding from the cylinder occurred was found to be higher than that for a uniform stream and increased approximately linearly with increasing shear parameter when it was larger than about 0·06. In the Reynolds-number range 43 < Re < 220, the vortex shedding disappeared for sufficiently large shear parameters. Moreover, in the Reynolds-number range 100 < Re < 1000, the Strouhal number increased as the shear parameter increased beyond about 0·1.

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.

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