VORTEX PAIRING IN A CIRCULAR JET UNDER CONTROLLED EXCITATION - 2. COHERENT STRUCTURE DYNAMICS.

The coherent structure dynamics in the near field of a circular jet has been experimentally explored by inducing ″stable″ vortex pairing through controlled excitation and applying phase-averaging techniques. At a particular phase during the pairing process, spatial distributions of the phase-average longitudinal and lateral velocity perturbations, vorticity, streamlines, the coherent and background Reynolds stresses and turbulence intensities have been educed. Spatial distributions of these measures at four successive phases during the pairing process are also educed. The flow physics is discussed on the basis of measurements over the physical extent of the vortical structures, phase-locked to specific phases of the pairing event and thus do not involve use of the Taylor hypothesis. Refs.