Vortex Wall Research Articles

Ozone profile measurements within, at the edge of, and outside the Antarctic polar vortex in the spring of 1988

Ozone and temperature were measured during 38 balloon soundings at McMurdo Station, Antarctica (78° S), in the spring of 1988. Because of the motion of the Antarctic polar vortex, measurements were obtained within, at the edge of, and outside the vortex. Although the polar vortex did not remain over McMurdo as it did in 1986 and 1987, it was overhead long enough to establish that ozone depletion was less extensive and ended earlier than in either 1986 or 1987. In the vortex the ozone mixing ratio at 18 km decayed with an exponential half‐life of 29 days compared to 25 and 12 days in 1986 and 1987. While ozone partial pressure in the 16–18 km layer decayed to values as low as 10 nbar in 1986 and 3 nbar in 1987, ozone partial pressure dropped to only 60–70 nbar in 1988 in the depleted region, a reduction of 30 to 50%. Even with these differences in degree of ozone depletion there were similarities to previous measurements. Ozone depletion was caused by a sink between 12 and 20 km, and primary depletion was episodic, occurring in periods of <10 days. Measurements at the edge of the vortex displayed the ozone layering observed in 1986 and 1987 and suggest the exchange of ozone rich and poor air across the vortex wall in the 12–20 km layer. Outside the vortex, vertical profiles displayed a region of high ozone and constant temperature above 20 km.

Numerical micromagnetics: rectangular parallelopipeds

Results of simulations of magnetization reversal in rectangular Permalloy particles with aspect ratios 10*5*1 are given. Magnetization patterns during nucleation of reversal in the remanent state and after the applied field is reversed are shown in detail for the case of an applied field along the long axis of the particle. The nucleation and remanent state behaviors are also illustrated in lesser detail for other applied field directions. The remanent state is the classical four-domain pattern, although the seven-domain pattern also appears. The longest wall in the four-domain pattern is a vortex wall.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Wall vortex induced by and moving with a confined vortex pair

A wall vortex was found, which was induced by, and moved together with, a confined vortex pair, near the parallel plates between which the confined vortex pair was traveling. The generation of the wall vortex can be attributed to the boundary layer separation that was caused by the characteristic flow field of the vortex pair itself.

Quasimolecular channel and vortex street modeling on a supercomputer

A quasimolecular model is developed for the simulation of vortex development in prototype fluid flow problems. The approach is formulated mathematically as an n-body problem which incorporates classical molecular type forces. Large systems of ordinary differential equations are generated and solved numerically on a Cray X-MP/24. A variety of examples in E 2 are described, including the development of Karman type vortices, wall vortices, and paired vortices.

Flow field calculation and its experimental verification for inertia stage of marine gas turbine air intake filter

A numerical method is presented in this paper for the solution of flow field in marine gas turbine air intake filtration channel. The flow field was successfully calculated by this method, and aerodynamic characteristics were obtained for various types of filtration channels. This work is expected to be of practical importance for the design of such filters. Upstream difference was adopted to discretize the non-conservative type N-S equation for two-dimensional, time-dependnet, viscous and incompressible flow, and the stability, convergence, accuracy and artificial viscosity of the resulting difference equation were examined. This equation can be used to calculate viscous flows with Reynolds number up to tens of thousands. Also presented in this paper is a calculation method for treating wall vortex at boundary inflection points. Careful studies show that calculation based on the difference equational and wall vortex treatment proposed here are in good agreement with experimental results.

Sensing-area distribution functions for one- and three-loop superconductive magnetic-monopole detectors.

We have calculated the response of the existing one- and three-loop superconductive magnetic-monopole detectors to an isotropic distribution of monopole trajectories passing through the detectors. The effective sensing area of the three-loop detector is shown to be 476 ${\mathrm{cm}}^{2}$ for events greater than 0.1${\ensuremath{\Phi}}_{0}$ (${\ensuremath{\Phi}}_{0}$=hc/2e) in at least two of the three loops. These calculations include the effects of the cylindrical superconducting shields surrounding the loops. First the interior magnetic-field distribution within the cylindrical shield is found for a doubly quantized vortex located in the shield wall. Next the coupling of this field to each superconducting loop is computed as a function of the position of the vortex relative to the loop. Then the current change induced in the loops is found for each monopole trajectory by combining the direct coupling to the entering and exiting cylinder wall vortices. The one- and three-loop sensing-area distribution functions are then found using a Monte Carlo technique on a large number of isotropically distributed trajectories.

Flowfield analysis of low bypass ratio test cells

THE operation of an engine test cell at low bypass ratios tends to amplify many adverse flow effects. This synoptic presents the results of a technique for test cell analysis called the combination technique which is a derivative of a threedimensional panel methods code. The results are compared to experimental data and when coupled with experimental data show that flow separation from the test-cell walls occurs at all cell bypass ratios. The results also indicate a relationship between this wall flow separation and vortex formation and ingestion. This technique represents a simple method to obtain an accurate aerodynamic analysis of a complex threedimensional flowfield in an engine test cell. Nomenclature Cp = pressure coefficient based on front cell pressure DF - fan diameter KBF = bypass flow velocity at highlight j/FC = front cell velocity X = station XUL = highlight station is composed of the test-cell walls, the engine with a bellmouth, and the engine thrust frame. The test-cell walls are square in cross section and impervious to the flow. The thrust frame is modeled by a solid enclosure. The bellmouth is modeled both internally and externally. To induce the engine flow, a nonzero normal velocity is imposed on the fan face. The core

Observations of magnetic domain structures in thick foils of Ni-Fe-Co-Ti alloy

The domain structure of thick foils of a 33.8Ni-51.0Fe-14.0Co-1.2Ti (wt%) alloy has been studied by high voltage transmission Lorentz microscopy. Complex domain structures and wall images have been observed. Periodic domain structures have been interpreted as sets of two-dimensional vortex walls.

Effect of wall friction and vortex generation on the radial distribution of different phases

Arguments are presented to prove the existence of rolling vortices in single-phase and two-phase flow. In the liquid phase, they appear in a boundary layer near a wall while in the continuous vapor phase they occur near the interface with a liquid film. The intensity and size of these vortices depend on the local velocity gradients normal to the wall. The interaction between the rotational field associated with such vortices and bubbles in liquid flow or droplets in vapor flow is discussed. This interaction may be called the wall-vortex effect. It appears that several, apparently unrelated, phenomena observed in two-phase flow systems may be interpreted in terms of this mechanism. Among these are: (i) radial void peaking near the walls (ii) vapor velocities less than liquid velocity observed also in vertical upward flow (iii) reduced droplet diffusion near the liquid film and (iv) reduced vapor mixing between subchannels at low steam qualities. The cause of secondary flows in non-circular channels may also be explained in terms of rolling vortices near the walls. Finally, a comparison is made with the well known Magnus effect.

Unsteady Flow Past a Circular Cylinder Started Impulsively

The growth of the vortex-pair developed behind a circular cylinder was investigated experimentally, when the cylinder was moved impulsively in a water tank. The experimental conditions were Re = Ud/ν = 1022×103, d/h =0.040.67 where U is the cylinder speed, d the cylinder diameter and h the distance between side walls of the tank. The detailed patterns of the vortex sheets and path lines around the cylinder were visualized by means of electrolysis and Al-dust methods. When the ratio d/h is decreased to 0.1, the effects of the tank walls on the flow are substantially negligible. The vortex sheets roll up near the separation points when Re> 520 and a secondary small vortex-pair is formed on the upstream side of the main vortices. The pattern of the vortex sheets shedding from the secondary vortices changes as Re is increased. This phenomenon is closely related to the manner of growth and collapse of the main vortices. The wall effects were examined within the range of d/h = 0.10.67. When d/h>0.5, the separation of flow occurs also at the side walls and "wall vortices" are formed. These vortices deform the pattern of main vortices behind the cylinder.

Unsteady Flow Past a Circular Cylinder Started Impulsively

The growth of the vortex-pair developed behind a circular cylinder was investigated experimentally, when the cylinder was moved impulsively in a water tank. The experimental conditions were Re = Ud/ν = 1022×103, d/h =0.040.67 where U is the cylinder speed, d the cylinder diameter and h the distance between side walls of the tank. The detailed patterns of the vortex sheets and path lines around the cylinder were visualized by means of electrolysis and Al-dust methods. When the ratio d/h is decreased to 0.1, the effects of the tank walls on the flow are substantially negligible. The vortex sheets roll up near the separation points when Re> 520 and a secondary small vortex-pair is formed on the upstream side of the main vortices. The pattern of the vortex sheets shedding from the secondary changes as Re is increased. This phenomenon is closely related to the manner of growth and collapse of the main vortices. The effects were examined within the range of d/h = 0.10.67. When d/h>0.5, the separation of flow occurs also at the side walls and wall vortices are formed. These deform the pattern of main behind the cylinder.

Scale-Interaction Implications for the Waterspout Life Cycle. II

Abstract The high formation frequency and previously documented life cycle of Florida Keys' waterspouts result from energy and angular momentum cascades through five scales of atmospheric motion, namely the funnel, spiral, cumulus, cloud-line and synoptic scales. The funnel scale appears to be the most complicated in that pronounced horizontal and vertical flow asymmetries in the spray vortex and funnel-cloud walls have been quantitatively analyzed. Waterspouts are apparently a two-cell type of radial vertical circulation. The spiral scale of motion is first defined by sea surface spiral patterns during stage 2 of the waterspout life cycle. The spiral scale is important because it marks the primary waterspout growth phase and gives the first visual evidence of boundary layer rotation and inflow. The single-cumulus scale is important in providing updrafts and shower outflow for concentrating larger-scale vorticity. Motions on the cloud-line scale are perhaps most crucial for waterspout formation. Less than...