ASA 125th Meeting Ottawa 1993 May

1pNS3. The multiscale structure of the passive scalar field in turbulent water jets.

R. M. Everson

Ctr. for Fluid Mech., Brown Univ., Box 1966, Providence, RI 02912

K. R. Sreenivasan

Mason Lab., Yale Univ., New Haven, CT

The wavelet transform is applied to two-dimensional dye concentration data in axisymmetric turbulent jets at moderate Reynolds numbers. The transform permits an examination, at different scales, of the geometry of turbulent structures. Information about the number of structures at a given scale, their area and aspect ratio is obtained; long, stringy structures are observed at small scales in contrast to the short, rounded structures at large scales. The wavelet transform is also applied to temporally resolved sequences of laser-induced fluorescence images, which allows analysis of the evolution of structures at different scales, their interactions, and speeds. It is found that a significant part of the dynamics involves the merging of scales besides the usual splitting traditionally associated with cascading. Furthermore little coupling between structures at different scales is observed. A comparison with the vorticity field is made.