Visualization Of Vortex Structures Research Articles

Computational study on aeroacoustic fields of a transitional supersonic jet.

Aeroacoustic fields of a supersonic free jet at the Mach and Reynolds numbers of 2.1 and 70 000, respectively, of the transitional conditions are computationally investigated by large-eddy simulations. The supersonic transitional jets of different shear layer thicknesses without disturbances and those of the fixed shear layer thickness with disturbances are computationally investigated, and the effects of the shear layer thickness and the disturbance are discussed. The position of the transition and the turbulence intensity in the vicinity of the transition are clearly affected by those parameters. The turbulent fluctuation along the shear layer and the resulting intensity of the generated Mach waves are substantially attenuated by decreasing the shear layer thickness or adding the disturbance. A 5 dB increase in the sound pressure level is observed. This relatively lower increment in the sound pressure level compared with the 10-20 dB increase in the subsonic jet case is discussed as being due to the transition process promoted by the spiral mode in the supersonic jet case, unlike the axisymmetric case in the subsonic jet case. This point is confirmed by the linear stability analysis, the proper orthogonal decomposition analysis, and the visualization of vortex structures in the transition region.

Visualization of vortex structures and analysis of frequency of PVC

The paper presents the results of the study of large-scale vortex structures in a model chamber. Methods of forming quasi-stationary vortices of various shapes by changing the geometric parameters of the chamber have been proposed. In the model chamber with a tangential swirl of the flow, a rectilinear vortex, single helical and double helical vortices were obtained. The double helical structure of the vortex is unique due to its immovability around the axis of the chamber. The resulting structures slowly oscillate around their own axes, which is called the vortex core precession; while the oscillation frequency depends linearly on the liquid flow rate. The use of stationary vortex structures in power plants will increase the efficiency of combustion chambers and reduce slagging.

Visualization Of Vortex Structures In The Near Field Of The Round Jet Formed In Curved Channel By Piv-Method

The results of experimental investigation of the round jet with Dean vortices (Red = 4 000, De = 1 673) using Particle Image Velocimetry are presented. The measurements were performed with synchronization the phase of acoustic signal and a laser pulse. Instant picture of vorticity field ωz and vector velocity field for the U- and V-components of the jet cross-actions show Dean vortices near the output of the channel in the low velocity gradient field and Kelvin – Helmholtz vortices in the high-velocity gradient field. The presence of Dean vortices distorts two-dimensional vortex ring, which gets an Ω-shaped form, at that the « head» of Ω-vortex outpaces its «legs», as it is in a higher velocity area.

The Study by Visualization of Vortex Structures on a Warhead Wing,Apex Angle (?)=68.6?

This study has been given prominence and confirmed by extensive documentation while recent visualizations observed in a wind tunnel have revealed that rectilinear vortex flows from different angles interacting with one another above warheads. My experimental research has indicated the many and very specific series, by visualizations of wisps of smoke trails, of vortex structures of a preferential nature above a warhead where β=68.6°. The positioning of those structures has thus been determined with regard to the application of very general criteria governing the stability of vortex flows. What have also been exposed are the specific aspects of vortex flows together with some comments concerning the bursting of vortices above the warhead. The purpose of this study is to optimize the connection between marine, air and land forms such as sails, the wings of aircraft, cars and trains – and the stability of fluid flows around such forms.

Surface instability and primary atomization characteristics of straight liquid jet sprays

Using the detailed numerical simulation data of primary atomization, the liquid surface instability development that leads to atomization is characterized. The numerical results are compared with a theoretical analysis of liquid–gas layer for a parameter range close to high-speed Diesel jet fuel injection. For intermittent and short-duration Diesel injection, the aerodynamic surface interaction and transient head formation play an important role. The present numerical setting excludes nozzle disturbances to primarily investigate this interfacial instability mechanism and the role of jet head. The first disturbed area is the jet head region, and the generated disturbances are fed into the upstream region through the gas phase. This leads to the viscous boundary layer instability development on the liquid jet core. By temporal tracking of surface pattern development including the phase velocity and stability regime and by the visualization of vortex structures near the boundary layer region, it is suggested that the instability mode is the Tollmien–Schlichting (TS) mode similar to the turbulent transition of solid-wall boundary layer. It is also demonstrated that the jet head and the liquid core play an interacting role, thus the jet head cannot be neglected in Diesel injection. In this study, this type of boundary layer instability has been demonstrated as a possible mechanism of primary atomization, especially for high-speed straight liquid jets. The effect of nozzle turbulence is a challenging but important issue, and it should be examined in the future.