Passive Control Of Vortex Shedding In The Wakes Of Bluff Bodies
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Passive Control Of Vortex Shedding In The Wakes Of Bluff Bodies
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Author : John Clifford Owen
language : en
Publisher:
Release Date : 2001
Passive Control Of Vortex Shedding In The Wakes Of Bluff Bodies written by John Clifford Owen and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
Control And Suppression Of Laminar Vortex Shedding Off Two Dimensional Bluff Bodies
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Author : Andre Sirilutporn Chan
language : en
Publisher:
Release Date : 2012
Control And Suppression Of Laminar Vortex Shedding Off Two Dimensional Bluff Bodies written by Andre Sirilutporn Chan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
The focus of this research is on the control and suppression of vortex shedding of flow past bluff bodies. The motivation of this research stems from the aerodynamic problems encountered in the design and development of hard disk drives (HDD's). Two different computational fluid dynamic methods have been used in this research-- the Semi-Implicit Method for Pressure Linked Equation (SIMPLE), that is widely employed in today's commercial incompressible flow solvers, and the high-order spectral difference (SD) method, recently developed for compressible flow solution. In addition to numerical simulation and verification, complementary experimental measurements have been performed to further validate the results. This research leads to two very different suppression techniques: 1) a passive control using a thin splitter plate positioned downstream of the bluff body; 2) an active control by way of counter rotating a cylinder pair. The passive suppression technique places a thin splitter plate downstream of the bluff body in order to interfere with the vortex wakes and thereby suppress the vortexinduced forces on the bluff body itself. The present investigation examines the suppression of wake instabilities in the laminar shedding regime. Both bounded and unbounded flow conditions are examined. It is found that in the bounded flow condition, the channel walls have an additional stabilizing effect on the shedding control. With proper positioning of the splitter plate, vortex shedding is completely suppressed in a bounded flow with moderate blockage factor. Wind tunnel empirical experiments have also confirmed the effectiveness of a splitter plate in a bounded flow. Active flow control by counter-rotating a pair of cylinders has been numerically investigated. It has also been investigated experimentally in partnership with the Gas Dynamics Laboratory at Princeton University. It is demonstrated that it is possible to suppress unsteady vortex shedding for gap sizes from one to five cylinder diameters, at Reynolds numbers from 100 to 200. The degree of unsteady wake suppression is proportional to the speed and the direction of rotation, and there is a critical rotation rate where a complete suppression of flow unsteadiness can be achieved. In the doublet-like configuration at higher rotational speeds, a virtual elliptic body that resembles a potential doublet is formed, and the drag is reduced to zero. The shape of the elliptic body primarily depends on the gap between the two cylinders and the speed of rotation. Prior to the formation of the elliptic body, a second instability region is observed, similar to that seen in studies of rotating single cylinders. It is also shown that the unsteady wake suppression can be achieved by rotating each cylinder in the opposite direction, that is, in a reverse doublet-like configuration. This tends to minimize the wake interaction of the cylinder pair and the second instability did not make an appearance over the range of speeds investigated here.
Wake Dynamics And Passive Flow Control Of A Blunt Trailing Edge Profiled Body
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Author : Lakshmana Sampat Doddipatla
language : en
Publisher:
Release Date : 2010
Wake Dynamics And Passive Flow Control Of A Blunt Trailing Edge Profiled Body written by Lakshmana Sampat Doddipatla and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Wake flows behind two-dimensional bodies are dominated mainly by two types of coherent structures, namely, the Karman Benard vortices and the streamwise vortices, also referred to as rolls and ribs respectively. The three-dimensional wake instabilities lead to distinct instability modes (mode-A, mode-B and mode-C or mode S) depending on the flow Reynolds number and geometric shape. The present investigation explores the mechanism by which the flow transitions take place to three-dimensionality in the near wake of a profiled leading edge and blunt trailing edge body. Experiments consisting of a combination of Planar Laser Induced Fluorescence visualizations and Particle Image Velocimetry measurements are conducted for Reynolds numbers ranging from 250 to 46000. The results indicate that three instability modes, denoted by mode-A, mode-B and mode-C, appear in the wake transition to three-dimensionality, but their order of appearance does not occur through the traditional route as observed in circular cylinder flows. It is found that mode-C instability with a spanwise spacing varying between 1.2 to 2.8D (D being the trailing edge thickness) dominates the near wake development. This result is explored further with the aim to devise a simple passive control method to mitigate vortex shedding for blunt trailing edge bodies. The effect of a trailing edge spanwise sinusoidal perturbation (SSP) is investigated for a range of Reynolds numbers (ReD) spanning the transition range from ReD = 550 up to 46000. PIV measurements at different vertical and horizontal locations are performed to study changes in the streamwise and spanwise vortices. The base drag and strength of vortex shedding decrease with wavy trailing edge compared to the straight trailing edge. Proper Orthogonal Decomposition (POD) of the obtained PIV data indicates that the spanwise sinusoidal perturbation redistributes the relative energy, enhancing the streamwise vortices and, as a result, suppressing the Karman Benard rolls.
Vortex Shedding And Vortex Wakes Dynamics Instabilities And Modifications
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Author :
language : en
Publisher:
Release Date : 1994
Vortex Shedding And Vortex Wakes Dynamics Instabilities And Modifications written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1994 with categories.
RESEARCH OBJECTIVES: To study nonlinear and secondary instability properties of wake flows behind bluff bodies and their control and modification. (KAR) p. 2.
Control Of Two And Three Dimensional Wake Instabilities From Bluff Bodies
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Author :
language : en
Publisher:
Release Date : 1995
Control Of Two And Three Dimensional Wake Instabilities From Bluff Bodies written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1995 with categories.
The detailed, instantaneous flow structure of the near-wake of a cylinder subjected to various classes of active (open-loop) and passive control has been characterized using both qualitative flow visualization and high-image-density particle image velocimetry (piv) developed in our laboratories. The first cinema PIV system allows acquisition of images that are highly resolved in both space and time. Concepts of timing of vortex formation, period-doubled patterns of vortices, and modulated and phase-locked systems of vortices are addressed for controlled oscillations of the cylinder. Three-dimensional patterns of instantaneous vorticity allow classification of the modes of response of the near-wake, providing a basis for formulating concepts for attenuation of vortex formation.
Vortex Shedding From Elongated Bluff Bodies
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Author : Zachary John Taylor
language : en
Publisher:
Release Date : 2011
Vortex Shedding From Elongated Bluff Bodies written by Zachary John Taylor and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
As the spans of suspension bridges increase, the structures become inherently flexible. The flexibility of these structures, combined with the wind and particular aerodynamics, can lead to significant motions. From the collapse due to flutter of the Tacoma Narrows Bridge to the case of vortex-induced vibrations (VIV) of the Storebælt Bridge, it is evident that a better understanding of the aerodynamics of these geometries is necessary. The work herein is motivated by these two problems and is presented in two parts. In the first part, the focus is on the physical mechanisms of vortex shedding. It is shown that the wake formation for elongated bluff bodies is distinct from shorter bluff bodies due to the leading edge separating-reattaching flow. Pressure data are then used to propose a mechanism of competition between the flow at the leading and trailing edges rather than synchronization which occurs at low Reynolds numbers. Within the context of this framework, the wakes are orthogonally decomposed and it was discovered that new modes appear not previously observed for shorter bluff bodies. In Part II, a timeresolved Particle Image Velocimetry (PIV) system is developed. This system is used to capture both the high and low frequency dynamics of flutter due its uniquely long recording length. It is shown that, contrary to conventional understanding, the vortex shedding does not significantly change during flutter. Thus, the fact that these bodies shed vortices is only a secondary effect in relation to the flutter instability. There is a distinct contrast between flutter and VIV: the latter is known to be governed by the vortex shedding wake and it has been shown herein that the former is not. Regarding the problem of VIV, it is shown that the wakes of these bodies are formed due to interaction with the leading edge separating-reattaching flow. As the leading edge separation angle grows, it is shown to disturb the trailing edge vortex shedding altering many of the key parameters including fluctuating lift force and shedding frequency.
Twenty First Symposium On Naval Hydrodynamics
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Author : National Research Council
language : en
Publisher: National Academies Press
Release Date : 1997-09-11
Twenty First Symposium On Naval Hydrodynamics written by National Research Council and has been published by National Academies Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1997-09-11 with Science categories.
A Near Wake Study Of Vortex Shedding From Bluff Bodies At Low Reynolds Numbers
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Author : Anne Emily Corlett
language : en
Publisher:
Release Date : 1996
A Near Wake Study Of Vortex Shedding From Bluff Bodies At Low Reynolds Numbers written by Anne Emily Corlett and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1996 with categories.
Vortex Shedding From Stationary And Vibrating Bluff Bodies In A Shear Flow
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Author :
language : en
Publisher:
Release Date : 1980
Vortex Shedding From Stationary And Vibrating Bluff Bodies In A Shear Flow written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1980 with categories.
If a fluid is in relative motion past a stationary bluff, or unstreamlined, structure and the vortex shedding frequency approaches one of the natural frequencies of the structure, then resonant flow-induced oscillations of the structure can occur when the damping of the system is sufficiently low. These resonant oscillations are accompanied by a 'lock-on' or capture of the vortex shedding frequency by the vibration frequency over a range of flow speeds, and this lock-on effect causes the wake and the structure to oscillate in unison. The periodic lift and the mean drag forces are amplified as a result of the vibrations, and changes in these fluid forces are closely related to the changes that occur in the flow field in the near wake of the body. Many practical ocean and wind engineering situations involve lightly-damped structures that are located in flows of air or water that are nonuniform along the length of the structure. The primary difference between a uniform flow and a shear flow is the presence and added complexity, in a shear flow, of vorticity whose vector is normal to the plane of the flow. When the incident flow approaches the body this vorticity is turned into the flow direction and interacts with the vortices which are shed from the body into the wake.
Flow Control Techniques And Applications
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Author : Jinjun Wang
language : en
Publisher: Cambridge University Press
Release Date : 2018-12-13
Flow Control Techniques And Applications written by Jinjun Wang and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-12-13 with Science categories.
Master the theory, applications and control mechanisms of flow control techniques.
