The eduction of structures from flow imagery using wavelets Part I. The mixing layer

Using two-dimensional Mexican hat wavelets, digitized imagery from the flow visualization pictures of a mixing layer by Brown and Roshko have been analysed. The objective of the present study is to "calibrate" the proposed wavelet technique for educing structures in a flow whose large-scale organization is well established. It is found that, with appropriate thresholds on wavelet-transform coefficients, considerable insight into the structure of the flow at different scales can be obtained. In particular, the analysis reveals that the small-scale structure within the large-scale vortices is approximately homogeneous, and has characteristic scales that do not vary significantly with downstream distance.