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 experimentally investigated at an exit speed of 30 m/s. Streamwise evolutions of the profiles of mean velocities U and V; the fluctuation intensities u′, v′, and w′; and the Reynolds stress uv have been documented for the two asymptotic initial conditions: laminar and fully developed turbulent boundary layers. Even though these profiles achieve similarity well before the end of the potential core, the evolutions of the mixing layer width and peak values of u′, v′, w′, and uv show that the effects of the initial condition continue to persist until the end of the layer (Re_x ≈ 10⁶). The transverse separations between the peaks of w′, v′, uv and the mixing layer center have been discussed on the basis of their spatial distributions over the extent of the 'preferred mode' coherent structures educed in an axisymmetric mixing layer.