Unsteady Aerodynamics and Vortex Induced Aeroelastic Instability of a Structural Angle Section

1991 ◽  
Author(s):  
V. J. Modi ◽  
J. E. Slater
Keyword(s):  
Vortex Shedding ◽  
Degrees Of Freedom ◽  
Unsteady Aerodynamics ◽  
Two Dimensional ◽  
Vortex Control ◽  
Transmission Towers ◽  
Speed Range ◽  
Angle Section ◽  
Shedding Frequency ◽  
Vortex Capture

Abstract Wake-body interactions for a two-dimensional structural angle member during stationary and vortex induced oscillatory conditions are studied using a conventional low turbulence wind tunnel. The response of an angle section with combined plunging and torsion indicates that the oscillations occur essentially in one of the two degrees of freedom. The measurements of frequency and phase substantiated this observation. The plunging resonance exhibits the familiar vortex capture phenomenon where the shedding frequency is controlled by the cylinder motion over a finite wind speed range. On the other hand, the torsional vibration shows a vortex control phenomenon where the vortex shedding governs the frequency of oscillation. The vortex induced torsional resonance was found to be severe even at moderate damping levels. The results should prove useful in structural designs such as high voltage transmission towers, antenna masts, bridges, etc. where angle sections are often used as secondary members.

Unsteady Aerodynamics and Vortex-Induced Aeroelastic Response of a Structural Angle Section

1994 ◽  
Vol 116 (4) ◽  
pp. 449-456 ◽  
Author(s):  
V. J. Modi ◽  
J. E. Slater
Keyword(s):  
Vortex Shedding ◽  
Degrees Of Freedom ◽  
Unsteady Aerodynamics ◽  
Aeroelastic Response ◽  
Vortex Control ◽  
Transmission Towers ◽  
Speed Range ◽  
Angle Section ◽  
Shedding Frequency ◽  
Vortex Capture

Wake-body interactions for a two-dimensional structural angle member during stationary and vortex induced oscillatory conditions are studied using a conventional low turbulence wind tunnel. The response of an angle section with combined plunging and torsion indicates that the oscillations occur essentially in one of the two degrees-of-freedom. The measurements of frequency and phase substantiated this observation. The plunging resonance exhibits the familiar vortex capture phenomenon where the shedding frequency is controlled by the cylinder motion over a finite wind speed range. On the other hand, the torsional vibration shows a vortex control phenomenon where the vortex shedding governs the frequency of oscillation. The vortex-induced torsional resonance was found to be severe even at moderate damping levels. The results should prove useful in structural designs such as high-voltage transmission towers, antenna masts, bridges, etc., where angle sections are often used as secondary members.

Flow past a rotationally oscillating cylinder

2013 ◽  
Vol 735 ◽  
pp. 307-346 ◽  
Author(s):  
S. Kumar ◽  
C. Lopez ◽  
O. Probst ◽  
G. Francisco ◽  
D. Askari ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Far Field ◽  
Two Dimensional ◽  
Flow Past ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Flow Visualizations ◽  
Hydrogen Bubble Technique

AbstractFlow past a circular cylinder executing sinusoidal rotary oscillations about its own axis is studied experimentally. The experiments are carried out at a Reynolds number of 185, oscillation amplitudes varying from $\mathrm{\pi} / 8$ to $\mathrm{\pi} $, and at non-dimensional forcing frequencies (ratio of the cylinder oscillation frequency to the vortex-shedding frequency from a stationary cylinder) varying from 0 to 5. The diagnostic is performed by extensive flow visualization using the hydrogen bubble technique, hot-wire anemometry and particle-image velocimetry. The wake structures are related to the velocity spectra at various forcing parameters and downstream distances. It is found that the phenomenon of lock-on occurs in a forcing frequency range which depends not only on the amplitude of oscillation but also the downstream location from the cylinder. The experimentally measured lock-on diagram in the forcing amplitude and frequency plane at various downstream locations ranging from 2 to 23 diameters is presented. The far-field wake decouples, after the lock-on at higher forcing frequencies and behaves more like a regular Bénard–von Kármán vortex street from a stationary cylinder with vortex-shedding frequency mostly lower than that from a stationary cylinder. The dependence of circulation values of the shed vortices on the forcing frequency reveals a decay character independent of forcing amplitude beyond forcing frequency of ${\sim }1. 0$ and a scaling behaviour with forcing amplitude at forcing frequencies ${\leq }1. 0$. The flow visualizations reveal that the far-field wake becomes two-dimensional (planar) near the forcing frequencies where the circulation of the shed vortices becomes maximum and strong three-dimensional flow is generated as mode shape changes in certain forcing parameter conditions. It is also found from flow visualizations that even at higher Reynolds number of 400, forcing the cylinder at forcing amplitudes of $\mathrm{\pi} / 4$ and $\mathrm{\pi} / 2$ can make the flow field two-dimensional at forcing frequencies greater than ${\sim }2. 5$.

scholarly journals Numerical Study of Flow Characteristics Around Confined Cylinder using OpenFOAM

2018 ◽  
Vol 7 (4.35) ◽  
pp. 617
Author(s):  
P. Mathupriya ◽  
L. Chan ◽  
H. Hasini ◽  
A. Ooi
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Vortex Formation ◽  
Plane Channel ◽  
Flow Characteristics ◽  
Strong Interactions ◽  
Two Dimensional ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency

The numerical study of the flow over a two-dimensional cylinder which is symmetrically confined in a plane channel is presented to study the characteristics of vortex shedding. The numerical model has been established using direct numerical simulation (DNS) based on the open source computational fluid dynamics (CFD) code named OpenFOAM. In the present study, the flow fields have been computed at blockage ratio, β of 0.5 and at Reynolds number, Re of 200 and 300. Two-dimensional simulations investigated on the effects of Reynolds number based on the vortex formation and shedding frequency. It was observed that the presence of two distinct shedding frequencies appear at higher Reynolds number due to the confinement effects where there is strong interactions between boundary layer, shear layer and the wake of the cylinder. The range of simulations conducted here has shown to produce results consistent with that available in the open literature. Therefore, OpenFOAM is found to be able to accurately capture the complex physics of the flow.

Computational Determination of the Modified Vortex Shedding Frequency for a Rigid, Truncated, Wall-Mounted Cylinder in Cross Flow

2014 ◽  
Author(s):  
Aimie Faucett ◽  
Todd Harman ◽  
Tim Ameel
Keyword(s):  
Vortex Shedding ◽  
Cross Flow ◽  
Classical Case ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
End Effects ◽  
Dimensional Solution ◽  
Horseshoe Vortices ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Flow around a rigid, truncated, wall-mounted cylinder with an aspect ratio of 5 is examined computationally at various Reynolds numbers Re to determine how the end effects impact the vortex shedding frequency. The existence of the wall and free end cause a dampening of the classical shedding frequency found for a semi-infinite, two-dimensional cylinder, as horseshoe vortices along the wall and flow over the tip entrain into the shedding region. This effect was observed for Reynolds numbers in the range of 50 to 2000, and quantified by comparing the modified Strouhal numbers to the classical (two-dimensional) solution for Strouhal number as a function of Reynolds number. The range of transition was found to be 220 < Re < 300, versus 150 < Re < 300 for the classical case. Vortex shedding started at Re ≈ 100, significantly above Re = 50, where shedding starts for the two-dimensional case.

scholarly journals Sudden and Gradual Alteration of Amplitude During the Computation for Flow Around a Cylinder Oscillating in Transverse or In-Line Direction

2009 ◽  
Author(s):  
La´szlo´ Baranyi
Keyword(s):  
Vortex Shedding ◽  
Oscillation Amplitude ◽  
Mean Square ◽  
Two Dimensional ◽  
Flow Around A Cylinder ◽  
Mean Values ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
State Curve ◽  
Line Direction

This study investigates the effect of altering oscillation amplitude on time-mean and root-mean-square values of force coefficients when plotted against amplitude of oscillation. The cylinder is placed in a uniform flow and is oscillated mechanically in transverse or in-line direction. The two-dimensional numerical computations are carried out at Re = 140 and 160, at 90% of the natural vortex shedding frequency. For in-line oscillation, jumps were found in the time-mean values of lift and torque. Both abrupt and gradual alteration of amplitude in the course of a computation had the effect of keeping the solution in one state curve, i.e., of conserving state, or inhibiting changes in vortex structure. Transverse oscillation displayed no jumps, and alteration of amplitude had no effect on the solution.

Measurements of Bluff Body Wake Flow Around a Conformable Flow Control Surface

2003 ◽  
Author(s):  
David A. Ericson ◽  
Michael Jonson ◽  
Gary Koopmann
Keyword(s):  
Flow Control ◽  
Vortex Shedding ◽  
Flow Separation ◽  
Bluff Body ◽  
The Body ◽  
Control Surface ◽  
Periodic Flow ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Shedding Frequency

The vortex street is a unique type of unsteady flow separation seen commonly in flow over a bluff body with a characteristic periodic wake. A consequence of the periodic flow is that the drag and lift forces acting on the body also oscillate periodically. When the wake shedding frequency is near a structural frequency, flow induced resonance will occur. The continuing interest in the study of vortex street generation is propelled by the ever-present nature of these flows in a variety of applications including aerodynamics, hydrodynamics and underwater acoustics. Recent advances in material science and the development of high power density actuators have led to the study of adaptive structure technology wherein the vorticity of periodic flows can be actively controlled by changing the ‘bluffness’ or shape of the body. In this paper, the development and experimental testing of a two-dimensional shape-variable flow control surface are discussed in relation to the generation and manipulation of periodic flow separation. Two series of wind tunnel tests were designed to evaluate the potential of the morphing structure that replaced a section of the trailing edge of a symmetric airfoil. The test section successfully demonstrated a smooth transition between three prescribed trailing edge profiles ranging from sharp to blunt. Unsteady pressure spectra were measured near the trailing edge for three different shape profiles over a range of speeds between 50 and 110 ft/s. The measured pressure spectra amplitudes were compared to previously-published surface pressure spectra of a similar, two-dimensional, blunt edge foil. A second set of tests was performed to measure the resulting flow field in the direction transverse to the flow and downstream from the airfoil. Velocity measurements were made using a traversing hot-wire probe at three trailing edge configurations and speeds of 50, 70 and 90 ft/s. The corresponding Reynolds number based on wake thickness ranged from 3.9–9.8 × 104. Measured vortex shedding frequencies varied between approximately 50 to 130 Hz at the different trailing edge profiles. This type of change in the vortex shedding frequency can be used to reduce flow-induced vibration and its associated noise generation by avoiding shedding frequencies at operating speeds that coincide with airfoil resonances.

Study on Wind-Induced Vibration of a Super-High Tower

2013 ◽  
Author(s):  
Zhiwei Chen ◽  
Caifu Qian ◽  
Guoyi Yang ◽  
Xiang Li ◽  
Lijun Yin
Keyword(s):  
Natural Frequency ◽  
Vortex Shedding ◽  
Natural Frequencies ◽  
Force Amplitude ◽  
Speed Range ◽  
Wind Actions ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Wind Induced Vibration ◽  
Karman’S Vortex

In this paper, wind-induced vibration of a super-high tower is numerically studied. The natural frequencies of the tower are calculated. Karman’s Vortex Street is simulated and the alternate lateral forces across the wind are obtained. It is found that with the wind speed range of 0–52.3m/s acting on the tower, the maximum vortex shedding frequency is lower than the second natural frequency of the tower. Resonance of the tower could occur at the first natural frequency with the horizontal force amplitude 241.5N/m. For high towers, it is suggested that the wind actions in across the wind and fatigue strength checks should also be considered in the design approach.

Turbulent Heat Transport in a Boundary Layer Behind a Junction of a Streamlined Cylinder and a Wall

1992 ◽  
Vol 114 (4) ◽  
pp. 840-849 ◽  
Author(s):  
D. E. Wroblewski ◽  
P. A. Eibeck
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Vortex Shedding ◽  
Turbulent Heat Flux ◽  
Temperature Fields ◽  
Turbulent Heat ◽  
Two Dimensional ◽  
Wake Region ◽  
Dimensional Boundary ◽  
Shedding Frequency

Measurements of the turbulent velocity and temperature fields were made in a heated boundary layer 14 diameters downstream of a junction of a tapered cylinder and a wall (ReD = 24,700). The boundary layer is strongly affected by the presence of large-scale unsteadiness arising from vortex shedding, which appears in the measurements as “turbulence” with a strong spectral component at the shedding frequency. The boundary layer exhibits three distinct spanwise regions: (1) the innerwake region, z/D<0.8, where vortex shedding effects are observed only in the spanwise component of the fluctuations; (2) the middle-wake region, 0.8<z/D<1.6, where strong vortex shedding is seen in all three components of the fluctuations; and (3) the outer-wake region, z/D>1.6, where the flow is approaching a two-dimensional boundary-layer flow. Cross-spectra of νθ indicate that vortex shedding increases the turbulent heat flux in the middle-wake region. However, peak values of the Stanton number and the eddy diffusivity are observed in the inner-wake region, where the cross-spectra of turbulent heat flux do not exhibit a peak near the shedding frequency, but do show an increase compared to a two-dimensional boundary layer over a much broader frequency range.

scholarly journals Base Pressure on a Blunt Base in Transonic Flow: Some Effects of Base Geometry and Bleed Air

1982 ◽  
Author(s):  
F. Motallebi ◽  
S. J. Edwards ◽  
J. F. Norbury
Keyword(s):  
Experimental Investigation ◽  
Vortex Shedding ◽  
Transonic Flow ◽  
Base Pressure ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Maximum Value ◽  
Narrow Slot ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

An experimental investigation has been carried out on an aerofoil-like body having a thick square-cut trailing edge. Measurements of base pressure have been made for a range of mainstream Mach numbers from 0.6 to 1.3. The results also include measurements of vortex shedding frequency and schlieren photographs. Bleed air was discharged through the blunt base using three different configurations: (i) A wide two-dimensional slot; (ii) A narrow two-dimensional slot; (iii) A series of accurately bored discrete holes, equal in total area to the narrow slot. As the rate of discharge of bleed air was increased from zero the base pressure was found to rise to a maximum value before falling again at higher rates of discharge. At zero incidence the three configurations gave similar results but when incidence was applied the results were markedly different for the wide and narrow slots.

The Influence of Boundary Layer Velocity Gradients and Bed Proximity on Vortex Shedding From Free Spanning Pipelines

1984 ◽  
Vol 106 (1) ◽  
pp. 70-78 ◽  
Author(s):  
A. J. Grass ◽  
P. W. J. Raven ◽  
R. J. Stuart ◽  
J. A. Bray
Keyword(s):  
Boundary Layer ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Combined Effects ◽  
Maximum Increase ◽  
Velocity Gradients ◽  
Large Velocity ◽  
Layer Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The paper summarizes the results of a laboratory study of the separate and combined effects of bed proximity and large velocity gradients on the frequency of vortex shedding from pipeline spans immersed in the thick boundary layers of tidal currents. This investigation forms part of a wider project concerned with the assessment of span stability. The measurements show that in the case of both sheared and uniform approach flows, with and without velocity gradients, respectively, the Strouhal number defining the vortex shedding frequency progressively increases as the gap between the pipe base and the bed is reduced below two pipe diameters. The maximum increase in vortex shedding Strouhal number, recorded close to the bed in an approach flow with large velocity gradients, was of the order of 25 percent.

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