Review—Vortex Shedding Lock-on and Flow Control in Bluff Body Wakes

1991 ◽  
Vol 113 (4) ◽  
pp. 526-537 ◽  
Author(s):  
O. M. Griffin ◽  
M. S. Hall
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
The Body ◽  
Periodic Flow ◽  
Cylinder Wake ◽  
Mean Flow ◽  
Near Wake ◽  
Strong Resonance ◽  
And Control ◽  
Rotational Oscillations

The results of recent experiments demonstrate that the phenomenon of vortex shedding resonance or lock-on is observed also when a bluff body is placed in an incident mean flow with a periodic component superimposed upon it. This form of vortex shedding and lock-on exhibits a particularly strong resonance between the flow perturbations and the vortices, and provides one of several promising means for modification and control of the basic formation and stability mechanisms in the near-wake of a bluff body. Examples are given of recent direct numerical simulations of the vortex lock-on in the periodic flow. These agree well with the results of experiments. A discussion also is given of vortex lock-on due to body oscillations both normal to and in-line with the incident mean flow, rotational oscillations of the body, and of the effect of sound on lock-on. The lock-on phenomenon is discussed in the overall context of active and passive wake control, on the basis of these and other recent and related results, with particular emphasis placed on active control of the circular cylinder wake.

Vortex Shedding and Lock-On in a Perturbed Flow

1993 ◽  
Vol 115 (2) ◽  
pp. 283-291 ◽  
Author(s):  
Mary S. Hall ◽  
Owen M. Griffin
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Reynolds Numbers ◽  
Vortex Street ◽  
Mean Flow ◽  
Strong Resonance ◽  
Resonance Flow ◽  
The Mean ◽  
Rotational Oscillations ◽  
Good Agreement

Vortex shedding resonance or lock-on is observed when a bluff body is placed in an incident mean flow with a superimposed periodic component. Direct numerical simulations of this flow at a Reynolds number of 200 are compared here with experiments that have been conducted by several investigators. The bounds of the lock-on or resonance flow regimes for the computations and experiments are in good agreement. The computed and measured vortex street wavelengths also are in good agreement with experiments at Reynolds numbers from 100 to 2000. Comparison of these computations with experiments shows that both natural, or unforced, and forced vortex street wakes are nondispersive in their wave-like behavior. Recent active control experiments with rotational oscillations of a circular cylinder find this same nondispersive behavior over a three-fold range of frequencies at Reynolds numbers up to 15,000. The vortex shedding and lock-on resulting from the introduction of a periodic inflow component upon the mean flow exhibit a particularly strong resonance between the imposed perturbations and the vortices.

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.

scholarly journals Spin-up in a tank induced by a rotating bluff body

1999 ◽  
Vol 388 ◽  
pp. 49-68 ◽  
Author(s):  
D. MAYNES ◽  
J. KLEWICKI ◽  
P. McMURTRY
Keyword(s):  
Steady State ◽  
Turbulent Diffusion ◽  
Bluff Body ◽  
Fluid Velocity ◽  
Tangential Velocity ◽  
The Body ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
Acceleration Rate ◽  
Time Required

Spin-up of a turbulent flow in a cylindrical tank caused by a rotating bluff body has been investigated using flow visualization, fluid velocity measurements, and hydrodynamic torque measurements. During the spin-up process three distinct temporal regimes exist. These regimes are: (i) a build-up regime where the torque and the tangential velocity fluctuations in the close proximity of the body remain constant; (ii) a decay regime where these quantities decay with power-law relations; and (iii) a mean flow steady state where these values remain relatively constant. Experiments were conducted in two tanks differing in volume by a factor of 80 and with a large range of bluff body sizes. A non-dimensional time scale, τ, based upon turbulent diffusion is determined and the tangential velocity fluctuations and torque coefficient start to decay at a fixed value of τ. Likewise, steady state is attained at a larger fixed value of τ. This time scaling is physically based upon the time required for momentum to be transferred over the entire tank volume due to turbulent diffusion, and is general for any body size, tank size, rotation rate, and acceleration rate.

Stability properties of forced wakes

2007 ◽  
Vol 579 ◽  
pp. 137-161 ◽  
Author(s):  
B. THIRIA ◽  
J. E. WESFREID
Keyword(s):  
Vortex Shedding ◽  
Mean Flow ◽  
Near Wake ◽  
Global Mode ◽  
Spatial Properties ◽  
Moderate Reynolds Number ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
The Stability ◽  
Selection Of

Thiria, Goujon-Durand & Wesfreid (J. Fluid Mech. vol. 560, 2006, p. 123), it was shown that vortex shedding from a rotationally oscillating cylinder at moderate Reynolds number can be characterized by the spatial coexistence of two distinct patterns, one of which is related to the forcing frequency in the near wake and the other to a frequency close to the natural one for the unforced case downstream of this locked region. The existence and the modification of these wake characteristics were found to be strongly affected by the frequency and the amplitude of the cylinder oscillation. In this paper, a linear stability analysis of these forced regimes is performed, and shows that the stability characteristics of such flows are governed by a strong mean flow correction which is a function of the oscillation parameters. We also present experiments on the spatial properties of the global mode and on the selection of the vortex shedding frequency as a function of the forcing conditions for Re = 150. Finally, we elucidate a diagram of locked and non-locked states, for a large range of frequencies and amplitudes of the oscillation.

Study of Buoyancy Induced Suppression of Cylinder Wake Instability Using Schlieren-Interferometry

2007 ◽  
Author(s):  
S. K. Singh ◽  
P. K. Panigrahi
Keyword(s):  
Vortex Shedding ◽  
Heat Input ◽  
Richardson Number ◽  
Shear Layers ◽  
Vortex Structures ◽  
Schlieren Image ◽  
Cylinder Wake ◽  
Mean Flow ◽  
Experimental Conditions ◽  
Thermal Buoyancy

The control of horizontal square cylinder wake using thermal buoyancy has been experimentally investigated at low Reynolds numbers. The cylinder with an aspect ratio of 60 is mounted in a vertical test cell. The cylinder is electrically heated such that the buoyancy aids to the inertia of the mean flow. The operating parameters i.e. Reynolds number (87–118) and Richardson number (0.065–0.171) are varied to examine the flow behaviour over a range of experimental conditions. Laser schlieren-interferometry has been used for visualization and analysis of flow structures. The complete vortex shedding sequence has been recorded using a highspeed camera. The suppression of vortex shedding by heat input has been demonstrated by schlieren image visualization, time traces of light intensity, corresponding power spectra and Strouhal number. The study provides new experimental information on processes and mechanisms involved in the heat-induced changes of the vortex structures under the influence of buoyancy. The formation length of the vortex structures increases with increase in Richardson number i.e. heating level. The sequence of instantaneous schlieren images show that shape of vortex structures becomes slender at a sufficiently high Richardson number and the vortices from opposite shear layers rub with each other without increasing the circulation level and the two shear layers combine to form a single plume. The plume becomes steady at critical value of heat input leading to suppression of vortex shedding. The corresponding spectra evolve from having a clear peak at the vortex shedding frequency to broadband spectra when vortex shedding is suppressed.

Part I: Chordwise Distribution of Fluctuating Pressure

1981 ◽  
Vol 32 (2) ◽  
pp. 97-110 ◽  
Author(s):  
R.H. Wilkinson
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Lift Coefficient ◽  
Relative Magnitude ◽  
The Body ◽  
Front Face ◽  
Two Dimensional ◽  
Fluctuating Pressure ◽  
Pressure Distributions ◽  
Dimensional Section

SummaryThe fluctuating loading on a cylindrical bluff body due to vortex shedding increases if the body is capable of vibration. This is a result of amplification of the fluctuating pressures around a two-dimensional section of the body together with an improvement of the spanwise correlation of the vortex shedding. Measurement of the fluctuating forces on the cylinder during this process gives no guide as to the relative magnitude of these effects. In this paper, root mean square fluctuating pressure distributions and pressure correlations across a chord are presented for a square cylinder with front face normal to the approach flow whilst stationary and during forced vibration. The fluctuating lift coefficient for a two-dimensional section of the cylinder and its maximum amplification during vibration are calculated.

scholarly journals Flow-Induced Vibrations of Single and Multiple Heated Circular Cylinders: A Review

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8496
Author(s):  
Ussama Ali ◽  
Md. Islam ◽  
Isam Janajreh ◽  
Yap Fatt ◽  
Md. Mahbub Alam
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Heat Exchangers ◽  
Power Plants ◽  
Bluff Body ◽  
The Body ◽  
Circular Cylinders ◽  
Fluid Forces ◽  
Spacing Ratio ◽  
Flow Induced Vibrations

This study is an effort to encapsulate the fundamentals and major findings in the area of fluid-solid interaction, particularly the flow-induced vibrations (FIV). Periodic flow separation and vortex shedding stretching downstream induce dynamic fluid forces on the bluff body and results in oscillatory motion of the body. The motion is generally referred to as flow-induced vibrations. FIV is a dynamic phenomenon as the motion, or the vibration of the body is subjected to the continuously changing fluid forces. Sometimes FIV is modeled as forced vibrations to mimic the vibration response due to the fluid forces. FIV is a deep concern of engineers for the design of modern heat exchangers, particularly the shell-and-tube type, as it is the major cause for the tube failures. Effect of important parameters such as Reynolds number, spacing ratio, damping coefficient, mass ratio and reduced velocity on the vibration characteristics (such as Strouhal number, vortex shedding, vibration frequency and amplitude, etc.) is summarized. Flow over a bluff body with wakes developed has been studied widely in the past decades. Several review articles are available in the literature on the area of vortex shedding and FIV. None of them, however, discusses the cases of FIV with heat transfer. In particular systems, FIV is often coupled to heat transfer, e.g., in nuclear power plants, FIV causes wear and tear to heat exchangers, which can eventually lead to catastrophic failure. As the circular shape is the most common shape for tubes and pipes encountered in practice, this review will only focus on the FIV of circular cylinders. In this attempt, FIV of single and multiple cylinders in staggered arrangement, including tandem and side-by-side arrangement is summarized for heated and unheated cylinder(s) in the one- and two-degree of freedom. The review also synthesizes the effect of fouling on heat transfer and flow characteristics. Finally, research prospects for heated circular cylinders are also stated.

An Experimental Study of the Flow Above the Free Ends of Surface-Mounted Bluff Bodies

2012 ◽  
Author(s):  
Noorallah Rostamy ◽  
David Sumner ◽  
Donald J. Bergstrom ◽  
James D. Bugg
Keyword(s):  
Boundary Layer ◽  
Flow Pattern ◽  
Vortex Shedding ◽  
Ground Plane ◽  
Separated Flow ◽  
The Body ◽  
Bluff Bodies ◽  
Near Wake ◽  
Square Prism ◽  
Karman Vortex

The flow around surface-mounted finite-height bluff bodies is more complex than the flow around a two-dimensional or “infinite” cylinder. The flow over the free end and the boundary layer flow around the body-wall junction strongly influence the near-wake flow pattern. Streamwise tip vortex structures interact in a complex manner with Kármán vortex shedding from the sides of the body, and are responsible for a downward-directed local velocity field in the upper part of the wake known as “downwash.” A second pair of streamwise vortex structures, known as the base vortices, is found close to the ground plane. Upstream of the body the familiar horseshoe vortex is found. The interactions between the tip vortices, base vortices, and Kármán vortex shedding are strongly influenced by the aspect ratio, AR = H/D (for height, H, and width, D), the Reynolds number, Re, and the relative thickness of the boundary layer, δ/D. The flow above the free ends of surface-mounted finite-height circular cylinders and square prisms was studied in a low-speed wind tunnel using particle image velocimetry (PIV). Cylinders and prisms of AR = 9, 7, 5, and 3 were tested at Re = 4.2 × 104. The bodies were mounted normal to a ground plane and were partially immersed in a turbulent flat-plate boundary layer with δ/D = 1.7. PIV measurements were made above the free ends in three vertical planes at different cross-stream locations (y/D = 0, 0.25, and 0.375). The ensemble-averaged streamlines, turbulence intensity and Reynolds shear stress fields were obtained in these planes. The PIV results provide insight into the separated flow above the free ends, including the effects of AR and body shape. For the finite square prism, the large, separated, recirculating flow region extends into the near-wake. For the finite circular cylinder, this region is smaller and the separated flow reattaches onto the free-end surface. For the square prism of AR = 3, considerable difference is seen in the free-end flow pattern compared to the more slender prisms of AR = 9, 7 and 5. In particular, a cross-stream vortex is formed due to interaction between the separated flow from the leading edge of the prism and the reverse flow over the free end. This vortex is seen in all three planes for AR = 3 but only in the symmetry plane for AR = 9, while for the finite circular cylinder the flow pattern above the free end seems to be the same in all three planes for all aspect ratios, consisting of a cross-stream vortex at approximately x/D = 0.

Vorticity measurements in the near wake of a circular cylinder at low Reynolds numbers

1993 ◽  
Vol 246 ◽  
pp. 675-691 ◽  
Author(s):  
R. B. Green ◽  
J. H. Gerrard
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Near Wake ◽  
Low Reynolds Numbers ◽  
Region Length ◽  
Low Reynolds ◽  
Definition Of

The technique of the particle streak method has been applied to the study of bluff-body wakes at low Reynolds number. Vorticity and shear stress were measured to an accuracy of 15–20%. The vortex shedding cycles at Reynolds number of 73 and 226 are shown and the differences between the two are highlighted. Quantitative descriptions of the previously described vortex splitting phenomenon in the near wake are made, which leads to a description of the vortex shedding mechanism at low Reynolds number. The definition of low-Reynolds-number formation region length is examined. The strength of shed vortices obtained from integration of the vorticity is compared with directly measured vortex strengths and with the results of two-dimensional numerical analysis.

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