A visual study of turbulent spots

Abstract

From the results of a flow visualization experiment, certain physical characteristics of a turbulent spot are suggested by the authors. The spot was artificially initiated at a point by a small intermittent wall jet. The authors also carried out experiments behind vibrating trip wires and observed the ‘signatures’ or ‘footprints’ of the A-shaped vortices seen by other workers. The fact that these ‘signatures’ are also observed in a turbulent spot leads one to suspect that these spots consist essentially of an array of A-shaped vortices. The formation of the spot is subsequently described in terms of three-dimensional disturbances of the cross-stream vortex filaments.The basic structure of the turbulent spot proposed here is similar to the suggested structure of fully developed turbulent boundary layers first put forward by Theodorsen (1955) and more recently by Bandyopadhyay & Head (1979).