Effects of initial spanwise perturbations and three-dimensionality in a plane mixing layer

An experimental study concerning the influence of small changaes in initial conditions on the near- and far-field evolution of the th ree-dimensional structure in a plane mixing layer has been conducted. A two-stream mixing layer with a velocity ratio of 0.6 was generated with the initial boundary layers laminar and nominally two-dimensional. The initial conditions were changed slightly by interchanging the high- and low-speed sides of the wind tunnel, while maintaining the same velocity ratio. The results indicate that, even with this minor change in initial conditions, the near-field regions of the two cases differ significantly, with the peak Reynolds stress levels varying by up to 100 percent. In addition, the distribution of the individual streamwise vortical structures differs in intensity and position for the two cases, although the overall qualitative description is comparable.