The spreading of self-excited hot jets by side jets

Abstract

A transitional, heated, axisymmetric air jet is investigated in the regime in which it is self-excited and develops a regular sequence of intense vortex ring structures. Seeding of the jet fluid and laser illumination reveals a star-shaped jet cross section with between two and six radial fingers. Each finger thereby represents a cut through a strong quasisteady side jet that is directed away from the main jet axis and is approximately planar. It is suggested that these side jets contribute prominently to the entrainment of all jets with strong primary vortex ring structures.