Nkr. Kevlahan et al., A COMPARISON OF DIFFERENT ANALYTICAL TECHNIQUES FOR IDENTIFYING STRUCTURES IN TURBULENCE, Applied scientific research, 53(3-4), 1994, pp. 339-355
Vortical structures play an important role in the kinematics and dynam
ics of turbulence, but in order to understand this role we require tec
hniques to identify and classify them. Proper Orthogonal Decomposition
(POD), conditional sampling with ensemble statistics, and conditional
sampling with conditional statistics are applied to a simple test fun
ction and the results are compared to determine the strengths and weak
ness of each approach. The second method gives the closest approximati
on to the test signal and is the easiest to use, although it is sensit
ive to the choice of conditions. None of these techniques can give muc
h insight into the dynamics of turbulence, or into the organisation of
eddies with complex, fine-scale structure. New methods for investigat
ing complex (self-similar) structures based on fractal and wavelet ana
lyses are presented. Methods of distinguishing between locally (accumu
lating) and globally (fractal) self-similar structures are suggested.