An Optimum Suppression of Fluid Forces by Controlling a Shear Layer Separated From a Square Prism

1991 ◽  
Vol 113 (2) ◽  
pp. 183-189 ◽  
Author(s):  
H. Sakamoto ◽  
K. Tan ◽  
H. Haniu
Keyword(s):  
Shear Layer ◽  
Vortex Shedding ◽  
Outer Boundary ◽  
Fluid Forces ◽  
Separated Shear Layer ◽  
Square Prism ◽  
Thin Region ◽  
Vortex Shedding Frequency ◽  
Lift And Drag ◽  
Control Cylinder

This paper deals with the suppression of the fluid forces by controlling a shear layer on one side separated from a square prism. The control of the separated shear layer was established by setting up a small circular cylinder (the control cylinder) in it on one side. Experimental data were collected to examine the effects on the fluid forces and vortex shedding frequency due to variation of the position and diameter of the control cylinder. The results show that (i) the maximum reduction of the time-mean drag and fluctuating lift and drag occurred when the control cylinder was located near what would ordinarily be considered the outer boundary of the shear layer; (ii) the control of the separated shear layer by means of a small cylinder appeared to be effective in suppressing the fluctuating lift and drag rather than the time-mean drag; (iii) in the case of the control cylinder of 6 mm in diameter, the time-mean drag was reduced to about 30 percent, and the fluctuating lift and drag were reduced to approximately 95 and 75 percent, respectively; (iv) the fluid forces and the frequency of vortex shedding of the square prism were mainly dependent on the characteristics of a very thin region near the outer boundary of the shear layer.

Suppression of Fluid Forces Acting on a Square Prism by Passive Control

1997 ◽  
Vol 119 (3) ◽  
pp. 506-511 ◽  
Author(s):  
H. Sakamoto ◽  
K. Tan ◽  
N. Takeuchi ◽  
H. Haniu
Keyword(s):  
Flat Plate ◽  
Vortex Shedding ◽  
Passive Control ◽  
Fluid Forces ◽  
Maximum Reduction ◽  
Square Prism ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Unsteady Fluid ◽  
Lift And Drag

Suppression of fluid forces acting on a square prism by passive control of the approaching flow was investigated in the present study. Flow was controlled using a small flat plate upstream of the prism. The position of the flat plate was varied within the range of S/W = 0 ~ 3.0 (S: distance between the flat plate and square prism, W: width of square prism) and the width h of the flat plate ranged from 2 mm to 8 mm (h/W = 0.05 ~ 0.19). Steady and unsteady fluid forces, vortex shedding frequency, and flow pattern were systematically investigated. The maximum reduction of time-averaged drag was 75 percent, and the maximum reduction in fluctuating lift and drag was 95 and 80 percent, respectively, using a flat plate 1/10 of the size of the square prism.

Optimum Suppression of Fluid Forces Acting on a Circular Cylinder

1994 ◽  
Vol 116 (2) ◽  
pp. 221-227 ◽  
Author(s):  
H. Sakamoto ◽  
H. Haniu
Keyword(s):  
Circular Cylinder ◽  
Flow Control ◽  
Flow Pattern ◽  
Vortex Shedding ◽  
Fluid Forces ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Unsteady Fluid ◽  
And Control ◽  
Control Cylinder

The objective of this paper is to investigate the suppression of the fluid forces acting on a circular cylinder (hereafter called the main cylinder) by controlling the flow around it. Flow control was established by introducing a fine circular cylinder (hereafter called the control cylinder) near the main cylinder. Measurements were carried out with variation of the position of the control cylinder in the ranges of G/d = 0.004 ~ 0.20 (G is the gap between main cylinder and control cylinder, d is diameter of main cylinder) and α = 0 ~ 180 deg (α is the angle along circumference from the front stagnation point of main cylinder) at a Reynolds number of 6.5 × 104. Subsequently, the steady and unsteady fluid forces, vortex shedding frequency and flow pattern were systematically examined. Furthermore, such matters as the mechanism of the flow control, the nature of the controlled wake, the relationship between the characteristics of the controlled fluid forces, and the behavior of the flow were discussed in detail on the basis of the obtained results regarding fluid forces, vortex shedding frequency and flow pattern.

scholarly journals On vortex shedding from an airfoil in low-Reynolds-number flows

2009 ◽  
Vol 632 ◽  
pp. 245-271 ◽  
Author(s):  
SERHIY YARUSEVYCH ◽  
PIERRE E. SULLIVAN ◽  
JOHN G. KAWALL
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Vortex Shedding ◽  
Coherent Structures ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Frequency Scaling ◽  
Separated Shear Layer ◽  
Low Reynolds Number Flows ◽  
Low Reynolds

Development of coherent structures in the separated shear layer and wake of an airfoil in low-Reynolds-number flows was studied experimentally for a range of airfoil chord Reynolds numbers, 55 × 103 ≤ Rec ≤ 210 × 103, and three angles of attack, α = 0°, 5° and 10°. To illustrate the effect of separated shear layer development on the characteristics of coherent structures, experiments were conducted for two flow regimes common to airfoil operation at low Reynolds numbers: (i) boundary layer separation without reattachment and (ii) separation bubble formation. The results demonstrate that roll-up vortices form in the separated shear layer due to the amplification of natural disturbances, and these structures play a key role in flow transition to turbulence. The final stage of transition in the separated shear layer, associated with the growth of a sub-harmonic component of fundamental disturbances, is linked to the merging of the roll-up vortices. Turbulent wake vortex shedding is shown to occur for both flow regimes investigated. Each of the two flow regimes produces distinctly different characteristics of the roll-up and wake vortices. The study focuses on frequency scaling of the investigated coherent structures and the effect of flow regime on the frequency scaling. Analysis of the results and available data from previous experiments shows that the fundamental frequency of the shear layer vortices exhibits a power law dependency on the Reynolds number for both flow regimes. In contrast, the wake vortex shedding frequency is shown to vary linearly with the Reynolds number. An alternative frequency scaling is proposed, which results in a good collapse of experimental data across the investigated range of Reynolds numbers.

Manipulation of the Flow Around a Circular Cylinder by Utilizing the Flow Receptivity

2007 ◽  
Author(s):  
Yasuaki Kozato ◽  
Satoshi Kikuchi ◽  
Shigeki Imao
Keyword(s):  
Circular Cylinder ◽  
Shear Layer ◽  
Vortex Shedding ◽  
Velocity Fields ◽  
Shear Layer Instability ◽  
Hot Wire ◽  
Acoustic Disturbance ◽  
Wire Probe ◽  
Separated Shear Layer ◽  
Karman Vortex

An attempt to control the flow around a circular cylinder by utilizing the receptivity to the external acoustic disturbance was carried out and its mechanism was also studied. The velocity fields around the cylinder vicinity are carefully investigated with an X-type hot-wire probe. When the disturbance of a higher frequency related to the separated shear layer instability is added, the development of turbulence and the spreading of the shear layer are restrained. And, the amplification of the fluctuating velocity component of the Karman vortex shedding is delayed and its degree is reduced. Furthermore, the process of the gradual scale modification of the shear layer instability that appears prior to the transition of the flow is suppressed.

scholarly journals Numerical Simulation on Vortex Shedding from a Hydrofoil in Steady Flow

2020 ◽  
Vol 8 (3) ◽  
pp. 195
Author(s):  
Jian Hu ◽  
Zibin Wang ◽  
Wang Zhao ◽  
Shili Sun ◽  
Cong Sun ◽  
...  
Keyword(s):  
Strouhal Number ◽  
Vortex Shedding ◽  
Angle Of Attack ◽  
Wake Flow ◽  
Trailing Edge ◽  
Inflow Velocity ◽  
Lift Curve ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Lift And Drag

This paper presents a numerical modeling procedure for the idealization of vortex shedding effects in the wake flow field of a NACA0009 hydrofoil. During the simulation, the lift and drag acting on the hydrofoil were monitored, and the vortex-shedding frequency of the hydrofoil was analyzed. The effects of inflow velocity, trailing-edge thickness, angle of attack, and maximum hydrofoil thickness on vortex shedding were investigated. The results indicate that an increase in the inflow velocity led to an increase in the vortex-shedding frequency and a negligible change in the Strouhal number. Furthermore, as the thickness of the trailing edge increased, the vortex-shedding frequency decreased gradually, whereas the Strouhal number first increased and then decreased. Vortex shedding and lift curve oscillations ceased altogether after the angle of attack of the hydrofoil increased beyond a certain threshold. When the maximum hydrofoil thickness was increased while keeping the thickness and chord length of the trailing edge constant, the vortex-shedding frequency decreased.

Suppression of Vortex Shedding of Circular Cylinder by a Small Control Rod

2013 ◽  
Vol 477-478 ◽  
pp. 265-270 ◽  
Author(s):  
Li-Chieh Hsu ◽  
De-Chang Lai ◽  
Jian-Zhi Ye
Keyword(s):  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Near Wake ◽  
Control Rod ◽  
Low Reynolds Numbers ◽  
Numerical Studies ◽  
Vortex Shedding Frequency ◽  
Physical Phenomena ◽  
Control Cylinder

The physical phenomena of vortex suppression and flow patterns by deploying a very mall control cylinder in the near wake region of a main cylinder in low Reynolds numbers is studied numerically. The control diameter effect on vortex suppression and three flow patterns has been studied. The results shows the control cylinder can reduce vortex shedding frequency and suppress shedding partially or completely dependent on the diameter of control cylinder and Reynolds number. The results of a cylinder with control and without control agree with experimental and numerical studies.

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