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| Experimental
and numerical models of the flows in cranked duct : Application
to the model of aortic crook |
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(see A4,
A5, A7, A18, A19, A21, C7, C16, C17, C30, C31, C43, C44)
As a part of a thesis work and then of an internship, an experimental
study is conducted since 1996 on a simplified model of aortic
crook. The main objective of this work is to analyze the effect
of "starting" of the physiological flows. At the beginning of
the cycle, physiologic signals start from a resting position,
in opposition to the simple oscillating flows which have an
initial velocity different from zero. This starting phenomenon
gives peculiar structures to the flows. A study of the transition
to turbulence has also been lead for this type of flow. Thanks
to recordings of the velocity by warm-film anemometry, a new
transition law was established. It refers to a new frequency
parameter associated to the time of systolic acceleration
We have also studied the secondary movements generated by this
type of flows in a cranked duct. An original test bench was
realized in order to produce oscillating and physiological flows
without no external perturbation. The instrumentation currently
used has allowed to quantify various values in the straight
part of the duct (pressure, flow debt, instant speed). |
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| Displays
obtained by laser tomography allowed to show the complexity
of the evolution of unsteady three-dimensional swirling structures
in the cranked duct. A parametric analysis in function of the
number of Dean and of the frequency parameter was conducted
to establish a classification for the flows. It is important
to note the strong influence of the effect of motion-starting
for these "starting flow" types. |
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| Development
of the secondary structures in a plan orthogonal to the axial
flow, for an angle of 120°. De = 310, a =
10.4, n = 3.9cPo, r
= 1065Kg/m3. |
Following these first results, numerical simulations were realized
on identical geometric models. The results show a good qualitative
agreement between numerical and experimental values.
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Comparison
of the experimental and numerical views for an angle of 60°,
De = 464, a
= 10.4, n = 3.9cPo, r = 1065Kg/m3 |
In order to compare the numerical and experimental models, velocities
measures in the cranked part are being made. Once the comparison
is established, we will be able to evaluate the comportment
of the parietal friction on the inside and outside linings of
the cranked part using numerical simulations; the parietal friction
is, as one should know, a physical value correlated to the development
of the intimous hyperlasy. |
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