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Starting vortex
About: Starting vortex is a research topic. Over the lifetime, 4785 publications have been published within this topic receiving 100419 citations.
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TL;DR: In this paper, the authors studied the dynamics of a vortex ring impacting a wall at normal incidence and showed that the secondary ring can develop azimuthal instabilities which grow rapidly owing to vortex stretching and tilting in the presence of the mean strain field generated by the primary vortex ring.
Abstract: Direct numerical simulations were used to study the dynamics of a vortex ring impacting a wall at normal incidence. The boundary layer formed as the ring approaches the wall undergoes separation and roll-up to form a secondary vortex ring. The secondary ring can develop azimuthal instabilities which grow rapidly owing to vortex stretching and tilting in the presence of the mean strain field generated by the primary vortex ring. The stability of the secondary ring was investigated through complementary numerical experiments and stability analysis. Both perturbed and unperturbed evolutions of the secondary ring were simulated at a Reynolds number of about 645, based on the initial primary-ring propagation velocity and ring diameter. The linear evolution of the secondary vortex-ring instability was modelled analytically by making use of a quasi-steady approximation. This allowed a localized stability analysis following Widnall & Sullivan's (1973) earlier treatment of an isolated vortex ring. Amplitude evolution and growth-rate predictions from this analysis are in good agreement with the simulation results. The analysis shows that the secondary vortex ring is unstable to long-wavelength perturbations, even though an isolated ring having similar characteristics would be stable.
70 citations
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TL;DR: In this paper, the dissipative dynamics of a vortex state in a trapped Bose-condensed gas at finite temperature were discussed and a scenario of decay of this state in static trap was drawn.
Abstract: We discuss dissipative dynamics of a vortex state in a trapped Bose-condensed gas at finite temperature and draw a scenario of decay of this state in a static trap. The interaction of the vortex with the thermal cloud transfers energy from the vortex to the cloud and induces the motion of the vortex core to the border of the condensate. Once the vortex reaches the border, it immediately decays through the creation of excitations. We calculate the characteristic lifetime of a vortex state and address the question of how the dissipative dynamics of vortices can be studied experimentally.
70 citations
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TL;DR: In this article, the effects of pulsation on the development of vortex rings and their penetration in a crossflow were investigated using flow visualization techniques including laser-induced fluorescence and hot-film anemometry.
Abstract: The spread and mixing of a fluid jet into an ambient stream occurs at a rate which deserves further study to improve efficient mixing. Mixing enhancement techniques, such as introduction of periodic disturbances into the jet flow, are used to increase mixing between a jet and the surrounding fluid. Pulsations were generated by the periodic closing and opening of a jet flow. The dynamics and trajectories of vortex rings, formed by the pulsation of the jet in a uniform crossflow, are studied. In particular, the effects of pulsation on the development of vortex rings and their penetration in a crossflow were investigated. Detailed measurements were made using flow visualization techniques including laser‐induced fluorescence and hot‐film anemometry. Vortex rings generated in a crossflow at one specific frequency (1 Hz) were measured using a hot‐film probe. Measurements indicated that vortex rings were fully‐formed at a distance of three times the jet exit diameter. To simulate the dynamics of vortex rings in...
70 citations
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TL;DR: In this paper, the propagation and interaction mechanisms demonstrated by compressible vortex rings are explored with spark shadowgraph and schlieren photography, and the vortical flow regimes produced by the impulse of a shock wave emerging from the open end of a tube are examined.
69 citations
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TL;DR: In this paper, the trajectories and circulations of vortices generated at sharp edges do not follow classical similarity-theory predictions for at least an initial short time, due to the effect of particular flow geometry (e.g., duct with wedge, nozzle) distant from the salient edge, axisymmetry, end effects, viscous diffusion, finite thickness of the detaching shear layer, and secondary vorticity caused by the interaction of the primary vortex with the edge at which it was generated.
Abstract: Various reasons have been given as to why the trajectories and circulations of vortices generated at sharp edges do not follow classical similarity-theory predictions for at least an initial short time. Amongst these are the effect of the particular flow geometry (e.g. duct with wedge, nozzle) distant from the salient edge (for rectilinear vortices); axisymmetry (for ring vortices); end effects (for rectilinear vortices); viscous diffusion; finite thickness of the detaching shear layer, as well as secondary vorticity caused by the interaction of the primary vortex with the edge at which it was generated. A further process that may be active is that of viscous entrainment. Experiments, in which essentially straight-line vortices were generated, indicate that of the seven possibilities mentioned, the first five do not play a significant part. All models consist of a basic flow onto which the modelled vortex is superposed. Thus either the basic flow or the vortex model are at fault. The basic flow onto which the vortex is superposed may well not be a pure edge flow, but one that is already taking on the character of an entraining jet flow. On the other hand, the vortex model fails to incorporate secondary vorticity which, particularly when rolled up, might be expected to be dynamically important.
69 citations