| Abstract: | The experimental technique of high-image-density particle image velocimetry makes it possible to resolve quantitatively instantaneous, two-dimensional sections of complex fluid flows. Detailed distributions of velocity in the plane of the section and instantaneous out-of-plane vorticity field can be calculated. The key features of complex flows, such as the onset of vortex breakdown, correspond to distinct topological structures of the vorticity field. It is often desirable to determine the location, size, and orientation of these topological structures in large sets of vorticity data. A mother wavelet function that imitates the topology of the vorticity field in the vicinity of breakdown has been constructed. The wavelet transform based on this mother wavelet is applied to the vorticity data. When the scale and orientation of the wavelet closely match those of the breakdown zone in the data sets, local signal maxima at the location of the breakdown can be observed in the corresponding transform planes. When the scale or orientation do not match, the peaks are not observed. With this approach, information on the location, size and orientation of the breakdown zone can be derived using the wavelet transform. The wavelet transform therefore serves as an effective means of pattern recognition, and has potential application to a broad range of problems in fluid mechanics. © 1996 John Wiley & Sons, Inc. |
