Behavior Of Vortex Rings Research Articles

Behavior of Vortex Rings

Behavior of Vortex Rings

Jet Noise Containing Discrete Frequency. 2nd Report. Effect of Structure and Behavior of Vortex Ring.

The effect of the structure and behavior of vortex rings on jet noise containing discrete frequency has been studied by digital image processing. In particular, the behavior of a series of vortex rings released from a nozzle with divergent exit angle was clarified by a high-speed video camera including Schlieren systems. The structures of vortex rings were classified into the following phenomena : chasing phenomenon in which a leading vortex ring was chased by a released vortex ring, merging phenomenon in which a released vortex ring merged after passing-through to a leading vortex ring, and rolling up phenomenon in which the main flow was rapidly rolled up after contraction. It was found that the discrete frequency was affected considerably by the vortex structure and behavior, and the characteristic frequency distributions for the above phenomena were presented. Furthermore, in spite of considerably lower pressure, violent discrete frequency and screech noise such as that generated by a supersonic jet were generated.

119 渦輪構造のジェット騒音に及ぼす影響

In this report, it was discussed by the digital image processing that the characteristics of the discrete frequency noise for subsonic jets were closely related to the structure and behavior of vortex rings. The vortex rings released from nozzle with exit divergent angle, were visualized by Schlieren method or a high-speed video camera included its system. It was clarified that the interaction of vortex rings were classified into phenomena of chasing, merging and rolling up and so on, and those phenomena had characteristic frequency distributions of noise respectively.

A modeling of vortex rings in an axisymmetric pulsed jet.

The behavior of vortex rings in the initial region of an axisymmetric pulsed jet was simulated by replacing an annular shear layer with a particular vorticity distribution by an array of discrete vortex ring filaments. This modeling was restricted to an inviscid and axisymmetric condition. Consequently, the detailed structure in a real jet cannot be explained by this model. Nonetheless, it provided a good representation of the rolling-up of the shear layer, the vortex ring formation and the transport velocity of the vortex ring. The experimental result, that the pattern of vortex ring formation was roughly classified into three types by Strouhal number, was also explained by this model. The behavior of the vortex ring after formation (for example, vortex ring coalescence) was successfully simulated by replacing a vortex ring by a single vortex ring filament. It was found that vortex ring motion in the initial region of a jet was essentially inviscid.

Effect of controlled pulsation on axisymmetric jet behavior.

Axisymmetric jets have been observed to investigate the effect of controlled pulsation on the behavior of vortex rings by using the hydrogen bubble technique and hot-film measurement. Pulsed jets had similar velocity profiles in the initial region and in the fully developed region. This similar velocity profile was coincident with that in natural jets. The differences between the two kinds of jets in volume rate, in decay of centerline velocity and in distribution of turbulent intensity, were observed to be remarkable in the initial region. Such differences were caused by the different behavior of vortex rings in the initial region. Behavior of vortex rings in the initial region of pulsed jets was roughly classified into three types by Strouhal number, Sr0 (Sr0 〈 0.9, 0.9 ≤ Sr0 〈 2.6, Sr0 ≥ 2.6). It was found that the pulsation for Sr0 = 0.3 was the most dispersive wave in a jet column.

Turbulent Vortices in Stratified Fluids

In the present paper, calculations, made with the finite difference axisymmetric WAKE computer code, of the influence of turbulence and stratification on the behavior of vortex rings are compared with experimental data. Calculations, made with the two-dimensional version of the code, are used to study the behavior of vortex pairs in stably stratified atmospheres for a range of Froude numbers. Stratification is shown to have a profound effect on the radius of a vortex ring descending into a stably stratified fluid. The separation of the vortices of a vortex pair remains nearly constant or decreases monotonically with increasing penetration of a stably stratified fluid, depending on whether the stratification is discontinuous or linear. An analysis based on an energy balance is used to assess the maximum descent of a vortex pair in a stably stratified fluid.

Behavior of vortex rings in the vicinity of a wall

An experiment is described which shows that a vortex ring traveling toward a wall situated normal to its axis may undergo momentary inversions of its forward velocity. A qualitative analysis of the physics involved is given.