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Y Zhou - One of the best experts on this subject based on the ideXlab platform.
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Flow induced vibrations of two circular cylinders in tandem arrangement part 1 characteristics of vibration
Journal of Wind Engineering and Industrial Aerodynamics, 2009Co-Authors: Sangil Kim, Md Mahbub Alam, Hiroshi Sakamoto, Y ZhouAbstract:Abstract This paper presents the results of an investigation on the Flow-induced vibration characteristics of two circular cylinders in tandem arrangement, with L/D=0.1–3.2 and reduced velocity Ur=1.5–26, where L is the gap spacing between the cylinders and D is the cylinder diameter. The cylinder vibration was restricted to a plane normal to the Incident Flow. Three different experimental conditions were examined: (i) both cylinders were allowed to vibrate; (ii) the downstream cylinder only was allowed to vibrate with the upstream cylinder fixed; and (iii) the upstream cylinder only was allowed to vibrate with the downstream cylinder fixed. Five Regimes I–V were identified, depending on L/D, fluctuating lift forces and vibration characteristics of the cylinders. In Regimes I (0.1≤L/D 6, including a divergent vibration of the upstream cylinder. In this regime, the vibration amplitude of the downstream cylinder is strongly dependent on whether the upstream cylinder is vibrating or fixed, whereas that of the upstream cylinder is weakly dependent on the downstream cylinder. In Regime III (0.6≤L/D
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Flow structure behind two staggered circular cylinders part 1 downstream evolution and classification
Journal of Fluid Mechanics, 2008Co-Authors: J C Hu, Y ZhouAbstract:Flow structures, Strouhal numbers and their downstream evolutions in the wake of two-staggered circular cylinders are investigated at Re=7000 using hot-wire, Flow-visualization and particle-image velocimetry techniques. The cylinder centre-to-centre pitch, P, ranges from 1.2d to 4.0d (d is the cylinder diameter) and the angle (α) between the Incident Flow and the line through the cylinder centres is 0° ∼ 90°. Four distinct Flow structures are identified at x/d ≥ 10 (x is the downstream distance from the mid-point between the cylinders), i.e. two single-street modes (S-I and S-II) and two twin-street modes (T-I and T-II), based on Strouhal numbers, Flow topology and their downstream evolution. Mode S-I is further divided into two different types, i.e. S-Ia and S-Ib, in view of their distinct vortex strengths. Mode S-Ia occurs at P/d ≤ 1.2. The pair of cylinders behaves like one single body, and shear layers separated from the free-stream sides of the cylinders roll up, forming one street of alternately arranged vortices. The street is comparable to that behind an isolated cylinder in terms of the topology and strength of vortices. Mode S-Ib occurs at α ≤ 10° and P/d > 1.5. Shear layers separated from the upstream cylinder reattach on or roll up to form vortices before reaching the downstream cylinder, resulting in postponed Flow separation from the downstream cylinder. A single vortex street thus formed is characterized by significantly weakened vortices, compared with Mode S-Ia. Mode S-II is identified at P /d = 1.2 ∼ 2.5 and α > 20° or 1.5 ≤ P/d ≤ 4.0 and 10°<α≤20°, where both cylinders generate vortices, with vortex shedding from the upstream cylinder at a much higher frequency than from the downstream, producing two streets of different widths and vortex strengths at x/d ≤ 5.0. The two streets interact vigorously, resulting in a single street of the lower-frequency vortices at x/d ≥ 10. The vortices generated by the downstream cylinder are significantly stronger than those, originating from the upstream cylinder, in the other row. Mode T-I occurs at P/d ≥ 2.5 and a = 20° ∼ 88°; the two cylinders produce two streets of different vortex strengths and frequencies, both persisting beyond x/d = 10. At P/d ≥ 2.5 and α ≥ 88°, the two cylinders generate two coupled streets, mostly anti-phased, of the same vortex strength and frequency (St≈0.21), which is referred to as Mode T-II. The connection of the four modes with their distinct initial conditions, i.e. interactions between shear layers around the two cylinders, is discussed.
T W Hartquist - One of the best experts on this subject based on the ideXlab platform.
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dynamical and pressure structures in winds with multiple embedded evaporating clumps i two dimensional numerical simulations
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: J M Pittard, J E Dyson, S A E G Falle, T W HartquistAbstract:Because of its key role in feedback in star formation and galaxy formation, we examine the nature of the interaction of a Flow with discrete sources of mass injection. We show the results of two-dimensional numerical simulations in which we explore a range of configurations for the mass sources and study the effects of their proximity on the downstream Flow. The mass sources act effectively as a single source of mass injection if they are so close together that the ratio of their combined mass injection rate is comparable to or exceeds the mass flux of the Incident Flow into the volume that they occupy. The simulations are relevant to many diffuse sources, such as planetary nebulae and starburst superwinds, in which a global Flow interacts with material evaporating or being ablated from the surface of globules of cool, dense gas.
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dynamical and pressure structures in winds with multiple embedded evaporating clumps i 2d numerical simulations
arXiv: Astrophysics, 2005Co-Authors: J M Pittard, J E Dyson, S A E G Falle, T W HartquistAbstract:Because of its key role in feedback in star formation and galaxy formation, we examine the nature of the interaction of a Flow with discrete sources of mass injection. We show the results of two-dimensional numerical simulations in which we explore a range of configurations for the mass sources and study the effects of their proximity on the downstream Flow. The mass sources act effectively as a single source of mass injection if they are so close together that the ratio of their combined mass injection rate is comparable to or exceeds the mass flux of the Incident Flow into the volume that they occupy. The simulations are relevant to many diffuse sources, such as planetary nebulae and starburst superwinds, in which a global Flow interacts with material evaporating or being ablated from the surface of globules of cool, dense gas.
J M Pittard - One of the best experts on this subject based on the ideXlab platform.
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dynamical and pressure structures in winds with multiple embedded evaporating clumps i two dimensional numerical simulations
Monthly Notices of the Royal Astronomical Society, 2005Co-Authors: J M Pittard, J E Dyson, S A E G Falle, T W HartquistAbstract:Because of its key role in feedback in star formation and galaxy formation, we examine the nature of the interaction of a Flow with discrete sources of mass injection. We show the results of two-dimensional numerical simulations in which we explore a range of configurations for the mass sources and study the effects of their proximity on the downstream Flow. The mass sources act effectively as a single source of mass injection if they are so close together that the ratio of their combined mass injection rate is comparable to or exceeds the mass flux of the Incident Flow into the volume that they occupy. The simulations are relevant to many diffuse sources, such as planetary nebulae and starburst superwinds, in which a global Flow interacts with material evaporating or being ablated from the surface of globules of cool, dense gas.
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dynamical and pressure structures in winds with multiple embedded evaporating clumps i 2d numerical simulations
arXiv: Astrophysics, 2005Co-Authors: J M Pittard, J E Dyson, S A E G Falle, T W HartquistAbstract:Because of its key role in feedback in star formation and galaxy formation, we examine the nature of the interaction of a Flow with discrete sources of mass injection. We show the results of two-dimensional numerical simulations in which we explore a range of configurations for the mass sources and study the effects of their proximity on the downstream Flow. The mass sources act effectively as a single source of mass injection if they are so close together that the ratio of their combined mass injection rate is comparable to or exceeds the mass flux of the Incident Flow into the volume that they occupy. The simulations are relevant to many diffuse sources, such as planetary nebulae and starburst superwinds, in which a global Flow interacts with material evaporating or being ablated from the surface of globules of cool, dense gas.
Pierre Ferrant - One of the best experts on this subject based on the ideXlab platform.
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simulation of wave body interaction using a single phase level set function in the swense method
ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013Co-Authors: G Reliquet, Aurelien Drouet, Pierreemmanuel Guillerm, E Jacquin, L Gentaz, Pierre FerrantAbstract:The purpose of this paper is to present combination of the SWENSE (Spectral Wave Explicit Navier-Stokes Equations – [1]) method — an original method to treat fully nonlinear wave-body interactions — and a free surface RANSE (Reynolds Averaged Navier-Stokes Equations) solver using a single-phase Level Set method to capture the interface. The idea is to be able to simulate wave-body interactions under viscous Flow theory with strong deformations of the interface (wave breaking in the vicinity of the body, green water on ship decks…), while keeping the advantages of the SWENSE scheme.The SWENSE approach is based on a physical decomposition by combining Incident waves described by a nonlinear spectral scheme based on potential Flow theory and an adapted Navier-Stokes solver where only the diffracted part of the Flow is solved, Incident Flow parameters seen as forcing terms.In the single-phase Level Set method [2, 3], the air phase is neglected. Thus, only the liquid phase is solved considering a fluid with uniform properties. The location of the free surface is determined by a Level Set function initialised as the signed distance. The accuracy of simulation depends essentially on the pressure scheme used to impose free surface dynamic boundary condition.Comparisons of numerical results with experimental and numerical data for US navy combatant DTMB 5415 in calm water and in head waves are presented.Copyright © 2013 by ASME
Dale R Durran - One of the best experts on this subject based on the ideXlab platform.
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vortex formation and vortex shedding in continuously stratified Flows past isolated topography
Journal of the Atmospheric Sciences, 1997Co-Authors: Christoph Schar, Dale R DurranAbstract:Abstract The Flow of a nonrotating atmosphere with uniform stratification and wind speed past an isolated three-dimensional topographic obstacle is investigated with a nonhydrostatic numerical model having a free-slip lower boundary. When the mountain is sufficiently high, the transient development of a quasi-steady Flow occurs in two phases. During the first phase, which occurs over a dimensionless time of O(1), the Flow is essentially inviscid and adiabatic, and potential vorticity (PV) is conserved. The transient evolution of the Flow during the second phase, which occurs over a dimensionless time of O(10) to O(100), is controlled by dissipation and is accompanied by the generation of PV anomalies. Two cases are examined in which the Flow is forced to remain left–right symmetric with respect to the axis of the Incident Flow. In the first, the dimensionless mountain height NH/U is 1.5, and gravity waves break over the mountain. In the second, NH/U = 3, and a quasi-steady recirculating wake containing a ...
