No abstract

The mean-velocity profiles and entrainment rates in the similarity region of a two-dimensional jet are generated by a simple superposition of Rankine vortices arranged to represent a vortex street. The spacings between the vortex centres, their two-dimensional offsets from the centreline, as well as the core radii and circulation strengths, are all governed by similarity relationships and based upon experimental data.Major details of the mean flow field such as the axial and lateral mean-velocity components and the magnitude of the Reynolds stress are properly determined by the model. The sign of the Reynolds stress is, however, not properly predicted.

The strongest indication of an ordered structure in the similarity region of plane jet flows is the well documented (but controversial) apparent “flapping” behavior. Previously, the negative correlation between probes placed on opposite sides of the jet centerline has been attributed to the periodic displacement of the mean velocity profile centerline about its average position, i.e., a flapping motion. The present investigation is directed at evaluating the premise of an essentially two-dimensional von Karman vortex street as being responsible for the apparent “flapping” behavior.

The variation of the maximum interface crossing frequency with respect to downstream position is shown to be consistent with the principles of similarity for the plane jet.