Wake Structure Behind Circular Cylinder by Plasma Actuators

2011 ◽  
Author(s):  
Shunsuke Yamada ◽  
Koui Shibata ◽  
Hikaru Yanagihara ◽  
Takahiro Doi ◽  
Hitoshi Ishikawa ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Bluff Body ◽  
Three Dimensional ◽  
Plasma Actuators ◽  
Dimensional Structure ◽  
Separation Flow ◽  
Driving Frequency ◽  
Dbd Plasma ◽  
Wake Structure ◽  
Body Boundary

The separation flow causes the decrease of the driving efficiency of the fluid machines. It is important to control the separation on the bluff body, boundary layer and so on. The purpose of the present study is to control the separation on a circular cylinder and investigate the wake structure using the induced by dielectric barrier discharge (DBD) plasma. The electrode of the DBD plasma was mounted. In previous study, it is reported that the three dimensional wake structures are effective for the drag reduction. We investigate the three dimensional structure of the wake due to three dimensional jets of plasma actuators. The plasma actuators have pulse driving frequency of 0, 0.22, 1.0 and 2.0. A voltage of 4 kVpp and a frequency of 10 kHz are applied to the electrode. The velocity profiles behind the circular cylinder were measured by X type hot-wire anemometer at a Reynolds number of 1.0 × 103. The wake structure changes because the roll up of vortex is suppressed using pulse driving of the plasma actuators. The effect of plasma actuators is evaluated based on the half width and Reynolds stress in the wake.

scholarly journals Direct Numerical Simulation of Flow around a Circular Cylinder Controlled Using Plasma Actuators

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
Taichi Igarashi ◽  
Hiroshi Naito ◽  
Koji Fukagata
Keyword(s):  
Numerical Simulation ◽  
Circular Cylinder ◽  
Direct Numerical Simulation ◽  
Drag Reduction ◽  
Three Dimensional ◽  
Reduction Rate ◽  
Plasma Actuators ◽  
Two Dimensional ◽  
Freestream Velocity ◽  
The Mean

Flow around a circular cylinder controlled using plasma actuators is investigated by means of direct numerical simulation (DNS). The Reynolds number based on the freestream velocity and the cylinder diameter is set atReD=1000. The plasma actuators are placed at±90° from the front stagnation point. Two types of forcing, that is, two-dimensional forcing and three-dimensional forcing, are examined and the effects of the forcing amplitude and the arrangement of plasma actuators are studied. The simulation results suggest that the two-dimensional forcing is primarily effective in drag reduction. When the forcing amplitude is higher, the mean drag and the lift fluctuations are suppressed more significantly. In contrast, the three-dimensional forcing is found to be quite effective in reduction of the lift fluctuations too. This is mainly due to a desynchronization of vortex shedding. Although the drag reduction rate of the three-dimensional forcing is slightly lower than that of the two-dimensional forcing, considering the power required for the forcing, the three-dimensional forcing is about twice more efficient.

scholarly journals The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel

2008 ◽  
Vol 603 ◽  
pp. 331-365 ◽  
Author(s):  
JAMES H. J. BUCHHOLZ ◽  
ALEXANDER J. SMITS
Keyword(s):  
Aspect Ratio ◽  
Strouhal Number ◽  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Dimensional Structure ◽  
Peak Efficiency ◽  
Thrust Coefficient ◽  
Wake Structure ◽  
Thrust Performance

Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. For ReC = O(104), thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel AR. Propulsive efficiency was sensitive to aspect ratio only for AR less than 0.83; however, the magnitude of the peak efficiency of a given panel with variation in Strouhal number varied inversely with the amplitude to span ratio A/S, while the Strouhal number of optimum efficiency increased with increasing A/S. Peak efficiencies between 9% and 21% were measured. Wake structures corresponding to a subset of the thrust measurements were investigated using dye visualization and digital particle image velocimetry. In general, the wakes divided into two oblique jets; however, when operating at or near peak efficiency, the near wake in many cases represented a Kármán vortex street with the signs of the vortices reversed. The three-dimensional structure of the wakes was investigated in detail for AR = 0.54, A/S = 0.31 and ReC = 640. Three distinct wake structures were observed with variation in Strouhal number. For approximately 0.20 < St < 0.25, the main constituent of the wake was a horseshoe vortex shed by the tips and trailing edge of the panel. Streamwise variation in the circulation of the streamwise horseshoe legs was consistent with a spanwise shear layer bridging them. For St > 0.25, a reorganization of some of the spanwise vorticity yielded a bifurcating wake formed by trains of vortex rings connected to the tips of the horseshoes. For St > 0.5, an additional structure formed from a perturbation of the streamwise leg which caused a spanwise expansion. The wake model paradigm established here is robust with variation in Reynolds number and is consistent with structures observed for a wide variety of unsteady flows. Movies are available with the online version of the paper.

Simulations of three-dimensional viscoelastic flows past a circular cylinder at moderate Reynolds numbers

2010 ◽  
Vol 651 ◽  
pp. 415-442 ◽  
Author(s):  
DAVID RICHTER ◽  
GIANLUCA IACCARINO ◽  
ERIC S. G. SHAQFEH
Keyword(s):  
Circular Cylinder ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Viscoelastic Flow ◽  
Dimensional Structure ◽  
Recirculation Region ◽  
Viscoelastic Flows ◽  
Cylinder Wake ◽  
Complex Flows

The results from a numerical investigation of inertial viscoelastic flow past a circular cylinder are presented which illustrate the significant effect that dilute concentrations of polymer additives have on complex flows. In particular, effects of polymer extensibility are studied as well as the role of viscoelasticity during three-dimensional cylinder wake transition. Simulations at two distinct Reynolds numbers (Re = 100 and Re = 300) revealed dramatic differences based on the choice of the polymer extensibility (L2 in the FENE-P model), as well as a stabilizing tendency of viscoelasticity. For the Re = 100 case, attention was focused on the effects of increasing polymer extensibility, which included a lengthening of the recirculation region immediately behind the cylinder and a sharp increase in average drag when compared to both the low extensibility and Newtonian cases. For Re = 300, a suppression of the three-dimensional Newtonian mode B instability was observed. This effect is more pronounced for higher polymer extensibilities where all three-dimensional structure is eliminated, and mechanisms for this stabilization are described in the context of roll-up instability inhibition in a viscoelastic shear layer.

The three-dimensional structure of the wake of a circular cylinder

1966 ◽  
Vol 25 (1) ◽  
pp. 143-164 ◽  
Author(s):  
J. H. Gerrard
Keyword(s):  
Circular Cylinder ◽  
Growth And Development ◽  
Free Stream ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
The Body ◽  
Dimensional Structure ◽  
Vortex Wake ◽  
Vortex Lines ◽  
Critical Scrutiny

A critical scrutiny of the nature of the three-dimensional characteristics of the vortex wake of a circular cylinder serves to suggest lines for further investigation and furnishes some ideas on the nature of the growth and development of these non-uniformities. It is suggested that the basic occurrence in the growth of three-dimensionality is the continuation of vortex lines, oriented more or less parallel to the body, into the direction of the free stream. The causes of this vary, as do the details of the development with the particular situation considered.Experiments were performed in a wind tunnel at Reynolds numbers based on cylinder diameter of 85, 235 and 2 × 104, at which stable, transitional and turbulent vortices were investigated.

Uniform Flow Past a Rotary Oscillating Circular Cylinder

2011 ◽  
Author(s):  
Lue Derek Du ◽  
Charles Dalton
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Uniform Flow ◽  
Resonance Phenomenon ◽  
Curvilinear Coordinates ◽  
Wake Structure ◽  
Flow Past ◽  
Wide Range

In this paper, we study uniform flow past a rotary oscillating circular cylinder computationally. The objective is to determine the effect the oscillating rotation has on the lift and drag forces acting on the cylinder, on the wake structure, and on vortex shedding. A combination of finite-difference and spectral methods is used to calculate the three-dimensional incompressible unsteady Navier-Stokes equations in primitive variable form in nonorthogonal curvilinear coordinates. Wake turbulence is modeled by an LES technique. The Reynolds number considered is Re = 1.5×104, which is the same as that in the experimental study of Tokumaru & Dimotakis (1991), who suggested this technique as a means of reducing drag. We fix the forcing amplitude at the moderate value of Ω = 2 and vary the forcing frequency in a wide range to study its effect on the flow. The resonance phenomenon and drag reduction effect are carefully examined. The wake structure and vortex shedding process is visualized by means of computational streaklines. These results have a practical application in offshore engineering.

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