Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session HI: Vortex Dynamics and 3D Vortex Flows V |
Hide Abstracts |
Chair: Charles R. Doering, University of Michigan Room: Tampa Marriott Waterside Hotel and Marina Meeting Room 5 |
Monday, November 20, 2006 2:00PM - 2:13PM |
HI.00001: The influence of pressure gradients on the development of spiral-type breakdown of a Batchelor vortex Spencer Sherwin, Michael Broadhurst Starting from a BiGlobal linear stability analysis, the development of helical instabilities on a jet-like Batchelor vortex are analysed using Direct Numerical Simulation (DNS). Initially, an axial periodicity is assumed in the streamwise flow direction, and the vortex is perturbed by the most unstable eigenmode. As this mode develops, there is a lateral expansion of the vortex into a helical structure, accompanied by a drop in axial velocity on the vortex core. The imposed axial periodicity limits the extent of this axial deceleration, and prevents a stagnation point -- indicative of vortex breakdown -- from developing. If the assumption of periodicity is relaxed, however, an abrupt and rapid deceleration of the vortex core is identified. The extent of this deceleration, and the time in which it develops, is very sensitive to external pressure gradients. For example, DNS indicates that breakdown develops more rapidly in an adverse pressure gradient. This cannot be analysed with a BiGlobal stability analysis, as there is an underlying assumption of axial homogeneity. Consequently, the Parabolised Stability Equations (PSE) for three-dimensional flows have been developed: The results of a PSE analysis agree with the DNS, confirming that an adverse pressure gradient is destabilising. [Preview Abstract] |
Monday, November 20, 2006 2:13PM - 2:26PM |
HI.00002: Flow Field Expression with Superposition of Dipole Kazuyuki Ueno, Yuko Matsumoto, Tsunenari Saitou Classical dipole in fluid mechanics has a singular point and the flow field around it is irrotational. In this study, extended dipole with rotational core region is introduced. It is a compact vortex pair in two-dimensional flow or a compact vortex ring in three-dimensional flow without singular points. Dipole moment of the extended dipole is related to rotation of vorticity, namely, Laplacian of velocity field. This relation gives general expression of induced velocity described with dipole moment and a compact kernel function of the core. This induced velocity has no singularity, automatically satisfies divergence-free condition for incompressible fluid, and is equal to classical dipole flow in far filed. Expression of an arbitrary flow field with superposition of the extended dipole is proposed. In case of continuous distribution of dipole moment, it results in a convolution integral. This convolution is discussed in association with the continuous wavelet transform. [Preview Abstract] |
Monday, November 20, 2006 2:26PM - 2:39PM |
HI.00003: Dipole method for incompressible flows and its test calculation of time evolution of a dipolar vortex Yuko Matsumoto, Kazuyuki Ueno A new numerical method to calculate an incompressible flow, a dipole method, is proposed. In the dipole method, a flow field is represented by superposition of many dipolar vortices, and these dipolar vortices are replaced ``dipole elements.'' The dipole elements move in fluid. Each dipole element is characterized by two variables, dipole moment and core radius. The dipole moment is a vector quantity whose direction is the same as the axis of the dipolar vortex. The core radius is an effective radius of rotational flow region of the dipolar vortex. These variables, changed with time, are determined by the momentum conservation law where the flow around the dipolar vortex is assumed to be irrotational. This dipole element has a self-induced velocity. Time evolutions of a dipolar vortex in two cases of background flows are simulated, the first case is a strain flow, and the second one is a rotational flow of the Rankin's vortex. The results of the dipole method are compared to numerical simulations using the vortex method with the same initial condition. [Preview Abstract] |
Monday, November 20, 2006 2:39PM - 2:52PM |
HI.00004: Maxial Enstrophy Generation in the 3D Navier-Stokes Equations Charles R. Doering, Lu Lu We address the following question for the 3D incompressible Navier-Stokes equations in a periodic domain: given an enstrophy budget, what incompressible flow field with that amount of enstrophy instantaneously maximizes the enstrophy generation rate? By solving the associated variational problem we have found flows that saturate the functional-analytic estimates (bounds) for the maximal rate of enstrophy production. We discuss implications of these results for the open question of existence and uniqueness of smoooth solutions of the 3D Navier-Stokes equations. [Preview Abstract] |
Monday, November 20, 2006 2:52PM - 3:05PM |
HI.00005: Experimental Characterization of Starting Jet Dynamics Carolina Marugan-Cruz, Geno Pawlak, Carlos Martinez-Bazan, Marcos Vera The dynamics of a laminar starting jet are explored in a series of laboratory experiments and numerical simulations. We identify new, objective methods for characterizing the leading vortex ring, enabling robust comparisons with results from a numerical model. Observations of circulation in the initial vortex ring and for the total jet are reported along with strain rate at the leading stagnation point. Growth and pairing of shear instabilities trailing the leading vortex ring is observed. Development of these secondary vortices and their subsequent interactions with the leading vortex has significant effects on the characteristics of the primary vortex ring. Strong fluctuations in strain rate at the leading edge are associated with the pairing of the initial vortex ring with a trailing secondary ring. [Preview Abstract] |
Monday, November 20, 2006 3:05PM - 3:18PM |
HI.00006: Three-dimensional structures in quasi-two-dimensional shallow flows R.A.D. Akkermans, A.R. Cieslik, L.P.J. Kamp, H.J.H. Clercx, G.J.F. van Heijst The extent to which an evolving dipole in a non-rotating shallow fluid layer can be considered as (quasi-) two-dimensional is addressed.~We present Stereo-PIV measurements at several horizontal fluid levels as well as 3D numerical simulations of this dipole evolution.~The experimental setup consists of a 52x52cm$^{2}$ square tank with a magnet below the bottom and two electrodes on opposite sides of the tank. A salt solution serves as the conducting fluid enabling electromagnetic forcing. The fluid layer is thin (up to 10 mm), thus 3D motions are suppressed by geometrical confinement. Due to the no-slip condition the flow is subjected to a vertical shear resulting in secondary circulations. Experimental results reveal significant vertical velocity in the frontal region of the dipole, as well as vertical motion inside the vortex cores. The dipole-wall collision shows the influence of the lateral side-wall on the flow, viz. vorticity production at the no-slip boundaries and subsequent advection of these vorticity filaments into the interior. The numerical simulations show good quantitative agreement with the experiments, and provide the full 3D velocity and vorticity field over the entire flow domain. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700