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| Titel |
Scaling properties of the velocity turbulent field from micro-structure profiles in the ocean |
| VerfasserIn |
X. Sanchez, E. Roget, J. Planella |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063546
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| Zusammenfassung |
| The statistical properties of the velocity field in the ocean, measured with an airfoil
mounted on a free falling micro-structure profiler, are characterized by studying
the scaling of the transverse structure functions in the inertial range, which are
determined by the intermittent nature of the turbulence. This is the first time, to our
knowledge, that the structure functions come from space series. Previous results in
air and in water were obtained from a static sensor in the atmosphere, the ocean
or in a laboratory setup. Furthermore, previous works are mainly focused on the
longitudinal structure functions, and the results we present here have to do with the
transverse structure functions. The p-order structure function S(p)(r), where r is the
two-point relative distance, exhibits in the inertial range for very high Reynolds number
homogeneous and isotropic turbulence a r-scaling S(p)(r) - rζ(p), or equivalently
a self-scaling S(p) -[S(3)]β(p) where β(p) = ζ(p)-ζ(3). For the longitudinal
structure functions, the Kolmogorov exact relation ζL(3) = 1 gives ζL(p) = βL(p),
but there isn’t any theoretical relation for the transverse scaling ζT(3), where we
refer to longitudinal and transverse functions with the subscripts L and T. The β(p)
self-scaling receives the name of extended self-similarity (ESS), because it presents an
extended scaling range in relation to the r-scaling. The ESS scaling has been even
measured in cases where the r-scaling doesn’t exist (low Reynolds number, for
instance). Furthermore, as has been reported by different experimental works, the
r-scaling is generally non universal, and depends on the degree of homogeneity,
isotropy or on the conditions of turbulence creation (Bolgiano scaling for thermal
convection, for instance). But the ESS scaling β(p) seems to follow a universal
behavior in a broad range of Reynolds numbers, degree of isotropy and conditions of
turbulence creation. First theoretical predictions on ζ(p) for 3D homogenous and
isotropic turbulence with very high Reynolds number were developed by Kolmogorov
(K41a), with the scaling ζ(p) = p-3, but posterior theoretical and experimental
refinements found a deviation or anomalous scaling from this linear trend with
origin in the intermittent nature of turbulence. The first open question we want
to study is if the longitudinal and transverse structure functions follow the same
kind of scaling, that is if ζT(p) = ζL(p), as is required by some theoretical results
for isotropic turbulence. To do this we compare our measured oceanic transverse
structure functions with previous works with longitudinal and transverse measures in
different mediums (water, air) and from different experimental approaches (ADV and
anemometers time series, -¦). The second question we study is if the ESS scaling
presents a universal behavior independent of the Reynolds number or the degree of
isotropy.
Acknowledgments: This research was developed under the Spanish Government Project
FIS2008-03608. |
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