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  • 1
    Electronic Resource
    Electronic Resource
    Numerical and experimental study of the interaction between a vortex dipole and a circular cylinder (1995)
    Springer
    Experiments in fluids 18 (1995), S. 153-163 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper describes a study of the centred collision between a dipolar vortex and a solid circular cylinder. The flow was analysed experimentally by using dye visualizations and streak photography. Flow characteristics such as vorticity fields and the transport of passive tracers were compared with numerical simulations. Observations revealed that thin layers of vorticity, created at the cylinder wall are advected by the primary dipole halves, which, while rolling up into compact patches, give rise to the formation of two new asymmetric dipoles that move away along curved trajectories. The structure of the vorticity distribution inside the dipole, before and after the collision, has been investigated. Both the numerical and the experimental results indicate that the vorticity patches originating from the original primary dipole approximately preserve their original functional relationship ω=f(ψ), while the secondary vorticity patches show a tendency to organize into structures attaining a similar relationship.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230259
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetically induced radiofrequency absorption in copper-oxide superconductors
    Amsterdam : Elsevier
    Physica C: Superconductivity and its applications 178 (1991), S. 197-202 
    Details
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0921-4534(91)90177-Z
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  • 3
    Electronic Resource
    Electronic Resource
    Vortex dipoles impinging on circular cylinders (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2196-2206 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vortex pairs interacting with a circular cylinder have been simulated by the numerical simulation of the two-dimensional Navier–Stokes equation in the vorticity streamfunction formulation. The interaction with a cylinder with a diameter equal to the diameter of the dipole has been simulated in the inviscid case with free-slip boundaries. This case has been considered as a way to perturb the initial dipole, which splits into two vortices that rejoin at a different location on the cylinder depending on the initial displacement of the cylinder from the centerline of the primary vortex pair. By the scatter plots it was shown that the Lamb dipole after the perturbation relaxes to its initial k2ψ functional relationship. The case of no-slip interaction has been considered when the cylinder is two orders of magnitude smaller than the dipole. The same features observed in the experiment of Homa et al. [J. Fluid Mech. 197, 571 (1988)] are obtained by the numerical simulations, that is a thin vorticity layer is generated at the cylinder, it rolls up and forms dipolar and tripolar structures, depending on the initial displacement of the cylinder from the centerline of the incoming dipole. Scatter plots of the vortex pair formed by the primary and secondary vorticity show a linear distribution similar to that of the Lamb dipole. The dependence on the Reynolds number has been investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858557
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  • 4
    Electronic Resource
    Electronic Resource
    Mixedness in the formation of a vortex ring (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 1513-1515 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mixing process in the formation of an axisymmetric vortex ring is analyzed by direct numerical simulation. After the initial phase, when the impulse is imparted to the fluid, the mixing increases linearly in time with a slope that is directly proportional to the vortex circulation (Γ) and to reactants diffusivity to the power −1/3 (Pe−0.33). In addition, for reacting flows with equivalence ratio (s) different from 1, it has been found that as s decreases the mixing first decreases and then increases. An explanation for this behavior is given. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868538
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  • 5
    Electronic Resource
    Electronic Resource
    Vortex rings descending in a stratified fluid (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 2819-2827 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental and numerical results are presented of a laminar vortex ring descending in a linearly stratified fluid. It is observed that the ring shrinks in size as it penetrates the stratified environment and has nearly disappeared when it comes to a stop. This behavior is similar to what was observed by Maxworthy [J. Fluid Mech. 81, 465 (1977)] for a turbulent vortex ring in a stratified environment. The ring position and size collapse on a single curve when appropriately scaled. It is shown that baroclinic vorticity production of opposite sign and cross diffusion is the cause for the disappearance of the ring. The instantaneous ring Froude number is always ≥1 and, therefore, no internal waves are generated. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869804
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  • 6
    Electronic Resource
    Electronic Resource
    Direct simulations of the transitional regime of a circular jet (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 751-759 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Accurate numerical simulations of temporal evolving round jets at a low Reynolds number have revealed the same features observed in experiments and vortex filament simulations. The initial layer of azimuthal vorticity, by the Kelvin–Helmholtz instability, produces vortex rings undergoing successive pairings leading to larger rings. Axisymmetric simulations have shown that the initial roll-up is not affected by the Reynolds number, consequently insights of practical importance on the transitional regime, can be obtained from low Reynolds number simulations affordable by numerics. The 3-D simulations displayed the formation of longitudinal structures, and their role in the spreading of the jet is described. Streamwise rib vortices develop in the braid region and these vortices are responsible for the creation of small scales, premonitory of turbulence. In analogy to the plane mixing layer, the pairing reduces the growth of longitudinal and radial vorticity components and triggers the transition to turbulence. Finally comparisons between azimuthal vorticity and passive scalar surfaces have revealed that the latter collects in fat structures while the vorticity is found in thin regions where it is augmented by stretching.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868313
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  • 7
    Electronic Resource
    Electronic Resource
    An explanation for anomalous vortex merger in rotating-tank experiments (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1411-1415 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theory and simulations based on the two-dimensional Euler equation predict a critical distance of separation for the merger of two like-signed vortices. By the symmetry of the equation, this separation must be the same for both cyclone and anticyclone pairs. In rotating-tank experiments, the observed critical separation distance for anticyclone merger is in accord with predictions; however, pairs of cyclones have been found to merge in all cases examined, even with separations substantially greater than the predicted critical separation. The hypothesis that this discrepancy is due to the presence of Ekman volume fluxes, which are not incorporated in the two-dimensional theory, is examined and found not quantitatively supportable. A second hypothesis is that the parabolic curvature of the free upper surface of the fluid in the rotating tank induces motion of the cyclones toward the center of the tank and hence promotes the cyclone pair merger. Quasigeostrophic simulations which capture this "topography effect'' show good agreement with the rotating-tank experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858019
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  • 8
    Electronic Resource
    Electronic Resource
    Helicity fluctuations and turbulent energy production in rotating and non-rotating pipes (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 2045-2056 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper finite-difference second-order accurate direct simulations have been used to investigate how the helicity density fluctuations change when a turbulent pipe rotates about its axis. In this case the rotation axis is parallel to the near wall vortical structures which play a fundamental role on the wall friction and turbulence production. The helicity density is the trace of the tensor γij′=〈vi′ωj′〉 whose elements form the components of v′×ω′. When the momentum equations are written in rotational form the turbulence energy production term splits into two parts, one related to the convection of the large scales and the other related to the energy cascade to the small scales. From data of direct simulations the changes of the turbulent production term profile with the rotation have been explained by the pdf of the v′×ω′ components. The links between the changes on the pdf of the v′×ω′ and the modifications of the vortical structures have been also investigated. The joint pdf of the dissipation with the helicity density has shown that the dissipation is highly correlated with regions of very low helicity density in the non-rotating pipe. When the pipe rotates the helicity density increases and the dissipation decreases. Since a drag reduction is one of the results of the background rotation, in this paper, it has been speculated that the alignment between velocity and vorticity could be a common feature in drag reducing flows. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869324
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  • 9
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    Unknown
    "COL1A2" Gene (alpha2 Gene of Type I Collagen) at the Haplotype Level As a New Valuable Anthropogenetic Marker: A Study on Sardinians (1994)
    Baltimore : Periodicals Archive Online (PAO)
    Human Biology. 66:4 (1994:Aug.) 613 
    Details
    ISSN: 0018-7143
    Topics: Biology
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:5243-1994-066-04-000007
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  • 10
    Electronic Resource
    Electronic Resource
    Numerical simulation of tripolar vortices in 2D flow
    Amsterdam : Elsevier
    Fluid Dynamics Research 9 (1992), S. 179-206 
    Details
    ISSN: 0169-5983
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0169-5983(92)90004-G
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