Probability Density Measurements in a Curved Mixing Layer

Probability density measurements of the turbulent velocities were made at several positions in a curved mixing layer. The probability densities reveal the intermittent nature of the flow, which is fully turbulent in the center of the mixing layer but nonturbulent far away from the mixing layer. By using an ``intermittency analyzer'' in combination with a pulse height analyser, the statistical properties of the ``fully turbulent'' flow were obtained. An important result of this study is that the ``apparent'' transfer of energy, which appeared to be up the energy gradient, is actually due to a difference in mean velocity between the fully turbulent and nonturbulent fluid. The nonturbulent fluid contained within the convex bulges of turbulent fluid fluctuates wildly in velocity, but is almost free of vorticity.