S. I. Shtork

Coherent helical structures in swirl flows

A nonstationary flow with rotating helical filaments formed in the region of swirl flow breakdown has been studied using the method of phase averaging of the output signal of a laser Doppler velocimeter. Vortices in the measured flow field were separated using the λ2 technique based on an analysis of the velocity gradient tensor. It is shown for the first time that precession of the central monopolar vortex is accompanied by the formation of a pair of secondary vortices with the opposite directions of circulation, which form a helical dipole structure.

Vortex reconnection in a swirling flow

Processes of vortex reconnection on a helical vortex, which is formed in a swirling flow in a conical diffuser, have been studied experimentally. It has been shown that reconnection can result in the formation of both an isolated vortex ring and a vortex ring linked with the main helical vortex. A number of features of vortex reconnection, including the effects of asymmetry, generation of Kelvin waves, and formation of various bridges, have been described.

The effect of air injection on the parameters of swirling flow in a Turbine-99 draft tube model

Results of experimental modeling of a swirling flow in a Turbine-99 draft tube prototype are presented. The influence of gas phase injection into the flow has been studied. Experiments were performed on a closed hydrodynamic setup containing a working stage with the Turbine-99 draft tube geometry. It is established that the gas content affects the flow structure. Gas injection leads to a change in the frequency of precession of the vortex core formed in the draft tube cone, which is not related to an increase in the gas-liquid mixture flow rate.

The influence of the dispersed gaseous phase on characteristics of vortex precession in a swirling gas–liquid flow

Vortex precession in a swirling gas–liquid flow with a dispersed gaseous phase in an axisymmetric hydrodynamic chamber is studied experimentally. Based on a visualization of the flow, phase separation in the flow with the formation of a floor vortex with a gaseous core along the axis is revealed. The measured dependences of the precession frequency and typical pressure differences in a hydrodynamic chamber on the consumption gas content in the flow made it possible to reveal a jumplike change in these characteristics in the region of low gas contents.

The Effect of the Air-Delivery Method on Parameters of the Precessing Vortex Core in a Hydrodynamic Vortex Chamber

The effect of the method of gas-phase injection into a swirled fluid flow on parameters of a precessing vortex core is studied experimentally. Conditions of the appearance of the vortex-core precession effect were modeled in a hydrodynamic sudden expansion vortex chamber. The dependences of the vortexcore precession frequency, flow-pulsation level, and full pressure differential in the vortex chamber on the consumption gas content in the flow have been obtained. The results of measurements permit one to determine optimum conditions for the most effective control of vortex-core precession.

Kelvin waves on helical vortex tube in swirling flow

Kelvin waves formed on precessing helical vortex tube after vortex reconnection were experimentally visualized. The experiments were performed in a swirling flow of viscous fluid in optically transparent conical diffuser. Vortex visualization was facilitated by cavitation in the vortex core and carried out using high-speed video cameras. Kelvin waves of zero, first and second modes m = 0, 1, 2 were formed in packets as a result of reconnection due to vortex tube self-intersection. Kelvin waves were observed to form both on the helical vortex tube and the detached vortex ring and to propagate along the axis of the vortex tubes.

Traveling vortex breakdown

A new type of propagating perturbations on a vortex filament-traveling vortex breakdown-has been observed experimentally. A method of controlled external action on a vortex flow with known parameters is used. Data are obtained on the absolute propagation velocity of the perturbations as a function of the conditions in the vortex chamber, which determine the vortex characteristics.