Helical vortices in swirl flow

Abstract

Helical vortices in swirl flow are studied theoretically and experimentally.A theory of helical vortices has been developed. It includes the following results: an analytical solution describing an elementary helical vortex structure – an infinitely thin filament; a solution for axisymmetrical vortices accounting for the helical shape of vortex lines and different laws of vorticity distribution; a formula for calculation of the self-induced velocity of helical vortex rotation (precession) in a cylindrical tube; an explanation of the zone with reverse flow (recirculation zone) arising in swirl flows; and the classification of vortex structures.The experimental study of helical vortices was carried out in a vertical hydrodynamical vortex chamber with a tangential supply of liquid through turning nozzles. Various vortex structures were formed owing to changing boundary conditions on the bottom and at the exit section of the chamber. The hypothesis of helical symmetry is confirmed for various types of swirl flow. The stationary helical vortex structures are described (most of them for the first time) the features of which agree with the results and predictions of the theoretical model developed. They are the following: a rectilinear vortex; a composite columnar vortex; helical vortices screwed on the right or on the left; a vortex with changing helical symmetry; a double helix – two entangled vortex filaments of the same sign.

Multiple helical modes of vortex breakdown

“…As the local circumferential velocity increases at the cavity centre the pressure decreases and, due to cavitation, forms thin air-filled continuous filaments (see figure 9, top row). From the air bubble visualizations of the helical vortices it is possible to estimate the dimensionless helical pitch τ (Alekseenko et al 1999) which is found to have the same value of approximately τ = 0.8, independent of the type of multiplet. By using the difference between the measured tangential velocity profiles and the analytical expression (2.3), it is possible to determine circulation ratios γ as well as δ, the ratio between the radius of the assigned flow and the radius of the multiplet.…”

“…Note that the same vortex model (2.3), in the sense of Batchelor's vortex (Batchelor 1964) or the q-vortex, is commonly used to describe experimental swirl flows (Faler & Leibovich 1978;Escudier 1988;Alekseenko et al 1999) and in instability studies of swirling flows (see Heaton & Peake 2007 and references therein).…”

Simulations of confined turbulent vortex flow

“…an influence of the downstream conditions on the entire flow), and vortex breakdown. Theoretical work on swirling flow [4,5] is often based on the Euler equations, leaving out turbulence. Industrial flows are, however, in many cases turbulent due to the large scale of the equipment, and high throughput.…”

Investigation a single-spiral vortex in a swirl flow

“…To carry out the experiments, a hydrodynamic stand created earlier in the IT SB RAS [2] to study turbulent swirling flow has been modernized. The hydrodynamic stand (Fig.…”

“…Longitudinal concentrated vortices increase the efficiency of devices and hardware systems. Stationary helical vortex structures were first observed at the Institute of Thermophysics of the SB RAS [2]. Until now, there is no quantitative information on such vortices that hinders understanding the physics of formation of vortices and developing approaches for mathematical description of the vortex dynamics.…”