Turbulence structure in the axisymmetric free mixing layer

The turbulence structure of the mixing layer of a 12.7-cm axisymmetric air jet discharging into a large room has been studied experimentally at an exit speed of 30 m/s. Streamwise evolutions of the profiles of mean velocities, velocity fluctuation intensities, and Reynolds stress were investigated for two asymptotic initial conditions: laminar and fully developed turbulent boundary layers. It is found that the effects of the initial condition persist until the end of the layer (to a Reynolds number of about 1-million). Transverse separations between peaks of intensity fluctuations and the mixing layer center are discussed on the basis of their spatial distributions over the extent of the 'preferred mode' coherent structures induced in an axisymmetric mixing layer.