Formation of Helical Structures in a Round Free Jet

Abstract

The paper deals with the formation of the coherent structures in the initial region of the axysymmetric free jet. Among the three forms of organized vorticity existing simultaneously in this kind of flow [1] an axisymmetric mode known as the dominant or preferred one which reaches the highest amplitude and therefore plays a dominant role in the “coherent” transport processes was taken under consideration. It is commonly assumed [2] that the development of vortex structures in the round jet takes place via the monotonic growth of radial oscillations of the mixing layer leading eventually to the rolling up of the vortex rings. The present measurment were concerned with the formation process of the vortex structures and that is why the whole mixing layer has been considered.