Experimental data obtained in various turbulent flows are
analysed by means of
orthogonal wavelet transforms. Several configurations are analysed: homogeneous
grid turbulence at low and very low Reλ,
and fully developed jet turbulence at moderate
and high Reλ. It is shown by means of the
wavelet decomposition in combination
with the form of scaling named extended self-similarity that some
statistical properties
of fully developed turbulence may be extended to low-Reλ
flows. Indeed, universal properties related to intermittency are
observed down to Reλ≃10.
Furthermore, the
use of a new conditional averaging technique of velocity signals, based
on the wavelet
transform, permits the identification of the time signatures of coherent
structures
which may or may not be responsible for intermittency depending on the
scale of
the structure itself. It is shown that in grid turbulence,
intermittency at the smallest
scales is related to structures with small characteristic size and with
a shape that may
be related to the passage of vortex tubes. In jet turbulence, the
longitudinal velocity
component reveals that intermittency may be induced by structures with
a size of
the order of the integral length. This effect is interpreted as
the signature of the
characteristic jet mixing layer structures. The structures identified
on the transverse
velocity component of the jet case turn out on the other hand not to be
affected by
the mixing layer and the corresponding shape is again correlated with the
signature
of vortex tubes.
Scalar structures around the mixing interface of a thermal mixing layer in multiscale-generated decaying turbulent flows visualized using DNS database
