Effects
of strain-rate and SGS dissipation rate on alignment trends
between large and small scales in turbulent duct flow
Bo Tao, Joseph Katz and Charles Meneveau
Department of Mechanical Engineering
The Johns Hopkins University
Baltimore, MD 21218
ABSTRACT: HPIV measurements of a turbulent flow in
a square duct are used for studying the 3-D geometric relations
between SGS stresses, filtered strain-rates and vorticity.
Conditional sampling is performed based on the strain magnitude
and SGS dissipation, including negative values. In regions
of high dissipation, the flow is more likely to be in axisymmetric
expansion with vorticity strongly aligned with the intermediate
strain-rate eigendirection. The alignment between the most
extensive SGS stress and the most compressive strain-rate
(Tao et al 2000) vary with both the dissipation and strain-rate
magnitude, with increased values of pdf peak in regions of
high dissipation and strain-rate magnitude. The relative
orientation pdfs of the other eigendirections exhibit
a more distinguishable bimodal behavior in regions of high
dissipation and strain-rate magnitude. However the alignments
still differ from eddy viscosity models. The paper also presents
the alignment pdfs between the measured stresses and
model stresses by similarity SGS models. It is shown that
the non-linear model (linearized similarity model) provides
much better predictions of the alignment, a trend that persists
in conditionally sampled data as well.
in:
Proceedings of ASME FEDSM00
ASME 2000 Fluids Engineering Division Summer Meeting
paper: FEDSM00-11164 (2000)
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see http://www.aps.org).