Helical vortices in swirl flow

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 str ucture - an infinitely thin filament; a solution for axisymmetrical vortice s accounting for the helical shape of vortex lines and different laws of vo rticity distribution; a formula for calculation of the self-induced velocit y of helical vortex rotation (precession) in a cylindrical tube; an explana tion of the zone with reverse flow (recirculation zone) arising in swirl fl ows; and the classification of vortex structures. The experimental study of helical vortices was carried out in a vertical hy drodynamical vortex chamber with a tangential supply of liquid through turn ing nozzles. Various vortex structures were formed owing to changing bounda ry conditions on the bottom and at the exit section of the chamber. The hyp othesis of helical symmetry is confirmed for various types of swirl flow. T he stationary helical vortex structures are described (most of them for the first time) the features of which agree with the results and predictions o f the theoretical model developed. They are the following: a rectilinear vo rtex; 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.