Direction Of Vortex Motion Research Articles

Duct sound produced by vortex flow over a splitter plate

This paper examines the sound generated by an inviscid low Mach number vortex filament as it moves near a semi-infinite splitter in a two-dimensional duct with and without vortex shedding at the splitter edge. A strong one-dimensional sound is produced when the vortex is close to the edge. Without vortex shedding, the sound is shown to consist of predominantly compressive pulses which propagate in the split duct section and a rarefaction pulse downstream of the splitter edge, regardless of the position of the half plate and the direction of vortex motion. The vortex shedding results in no horizontal force at and no sound going downstream of the edge. Results also suggest that the vortex shedding does not always result in noise reduction. In all cases with and without vortex shedding, the narrower section of the split duct experiences the most sound in general. The surprising result is found that the confinement of the edge-scattering flow within a duct does not much affect the high acoustic efficiency of the scattering process.

HYDRODYNAMIC CHARACTERISTICS OF VORTEX MOTION INSIDE THE HEMISPHERICAL DIMPLE

Experimental researches of the features of the generation and evolution mechanism of coherent vortex structures, which are formed inside the hemispherical cavity, and space-time characteristics of the fields of velocity and pressure fluctuations that they create, both within the cavity, and in its wake, were conducted. Experiments were carried out in hydrodynamic flume on the hydraulically smooth plate with hemispherical dimple. The symmetric and asymmetric large-scale vortical systems inside a dimple are found out depending on the flow regime, and location and periodicity of their ejections are shown. The evolution of tornado-like vortices subjected to a switch mechanism that is result in appearance of low-frequency modulating transversal oscillations of vortex motion inside the hemispherical dimple. The fields of velocity, dynamic and wall pressure fluctuations by a group of hot-films, miniature piezoelectric sensors of pressure fluctuations are studied. Space-time correlations of velocity and pressure fluctuations, which generate the coherent large-scale vortex structures, the circulation flow and the vortex structure of the shear layer, which are formed inside the hemispherical dimple and ejected out into the boundary layer, are obtained. It was determined that the largest values of the coefficient of the space-time correlations of the wall pressure fluctuations observed on the aft and side walls of the hemispherical dimple, and the lowest – in its forward bottom part. It was established that the cross-correlations of the longitudinal velocity fluctuations are higher than the cross-correlations of the velocity and wall pressure fluctuations, and the cross-correlations of the dynamic and wall pressure fluctuations. On the basis of short-time spectrum and correlation analyses, the non-stationary in tame and non-uniform in space characteristics of the coherent vortical systems inside and past the open dimple have been found. Temporal periodicity of cross-correlation characteristics of the wall pressure fluctuations between two sensors, located on the fixed distance corresponds to frequencies of the shear and wake modes of resonance oscillations in the dimple. Registration of the time lag, at which the cross-correlation or anticorrelation has maximum, enables to determine the group convective velocity of the coherent vortical structures during their formation and evolution, as well as the phase of development and direction of vortex motion inside the dimple.

Vortex motion in high- Tc films and a micropattern-induced phase transition

A micropattern-induced transition in the mechanism of vortex motion and vortex mobility is observed in high- T c thin films. The competition between the anomalous Hall effect and the guidance of vortices by rows of microholes (antidots) lead to a sudden change in the direction of vortex motion that is accompanied by a change in the critical current density and microwave losses. The latter effect demonstrates the difference in vortex mobility in different phases of vortex motion in between and within the rows of antidots.

Control of the vortex flow in microchannel arrays produced in YBCO films by heavy-ion lithography

High-energy heavy-ion lithography is a powerful tool for tuning both structural and electromagnetic properties of high temperature superconductors by inducing nanometer scale defects confined in micron scale patterns. We show how the vortex dynamics in YBCO thin films patterned by heavy-ion lithography can be controlled and potentially exploited for device applications. Both local critical temperature and local critical currents are effectively tailored by the imposed irradiation geometry. The direct visualization of the real-time dynamics of the magnetic pattern is achieved by the magneto-optical imaging technique, while confined vortex flow is revealed by the simultaneous measurement of the electrical resistance both along and perpendicular (Hall resistance) to the direction of the applied current. It is shown that, for microchannel arrays inclined with respect to the transport current flow, the direction of vortex motion is solely determined by the imposed irradiation pattern geometry, in a well-defined temperature range, for a given applied current.

Pattern induced phase transition of vortex motion in high-Tc films

A micropattern induced transition in the mechanism of vortex motion and vortex mobility is demonstrated for high-Tc films. The competition between the anomalous Hall effect and the guidance of vortices by rows of microholes (antidots) leads to a sudden change in the direction of vortex motion that is accompanied by a change of the critical current density and microwave losses. The latter demonstrates the difference in vortex mobility in the different phases of vortex motion in between and within the rows of antidots.

Experimental evidence for anisotropic response of a driven vortex lattice

We present kinetic inductance measurements in current driven Josephson junction arrays. Measurements performed with circular coils indicate that this technique is very sensitive to the vortex mobility. Results obtained with anisotropic detection coils provide experimental evidence for the anisotropic response of a driven vortex lattice. Anisotropic behavior is obtained when rising the temperature or the mean vortex velocity as indicated by the loss of the superconducting shielding capability, first in the direction of vortex motion and then in the perpendicular direction.

Dip effect in the hall angle of a type II superconductor

Measurements of the magnetic field dependence of voltages arising from vertex motion in a cold-rolled ribbon of Nb-1% Zr display a dip in the voltage longitudinal to the impressed electric current accompanied by a more pronounced dip in the Hall voltage. The direction of vortex motion in two dimensions as a function of applied field, as deduced from the observed voltages, is in qualitative agreement with existing theories of vortex pinning.