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.

The swirling flow in a lean premixed prevaporized (LPP) combustor model (LPP chamber) is studied, making use of high-speed photography, Laser Doppler Velocimetry (LDV), sound probes, fine-wire thermocouples, and suction probes for chemical gas analysis. The experimental study, which involved parametric changes of Re , S , and { , extends from the combustor primary zone to the premixing chamber and was conducted with and without reaction, burning either gaseous propane or liquid fuel assisted with preheated air at 300 °C. Measurements show that the swirling flow mixture that enters the primary zone of the combustor chamber shows evidence of a PVC structure, for S > 0.5, that embraces the central recirculation zone (CRZ). Furthermore, reaction test results show that increasing the swirl number decreases CO and NO x concentrations at the combustor exit and reduces flame stability limits to levels close to the lean limit because of flashback. In addition, a detailed study of the reacting condition ( S =1.05, { =0.5) was performed; the results indicate that the PVC is still present, embracing the base of the CRZ and staying in the inner shear layer, where the flame should also be stabilized, and contributing particularly to an abnormal radial distribution of W rms . Large gradients of mean temperature andUnburnedHydrocarbons(UHC) concentration were found to be limited to the base of the CRZ.