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fluidyn MP CHT
fluidyn MP CHT :
For all conjugate heat transfer problems.
Thermo-Hydro-Mechanical coupled
modeling
Modeling of heat exchange between fluids and
structures is challenging to obtain adequate accuracy in both. The
underlying constraint is that most of the numerical methods used,
can optimally model either fluids or structures but not both
simultaneously.
I n general the heat exchange
coefficient through the boundary layer is calculated with the help
of a computational fluid dynamics code, very often in Finite
Volumes. This coefficient is then used by a Finite Element code to
calculate the thermal conduction. The main problems in this practice
are:
- Thermal deformations in the structural surfaces, which are in
contact with fluid, may modify the boundary layer and
substantially change the heat exchange coefficient as well.
Accurate calculation of the thermal exchange is the most important
aspect as it influences the mechanical deformation. But, the
changes in the boundary layer due to the same thermal deformation
of the surfaces also modify it.
- Any transient phenomenon is difficult to simulate accurately
as the changes in boundary conditions and heat exchange
coefficients require several information exchanges between the CFD
code in Finite Volume and the structural mechanics code in Finite
Element.
A new approach to the simulation of
conjugate heat exchange has been used in the software fluidyn-MP CHT by
Strong coupling of the solvers:
Finite Elements (FE) for solids
& Finite volumes (FV) for
fluids
CONDUCTION, CONVECTION, AND
RADIATION
This new technology of strong
coupling manages simultaneously heat transfer and structural
deformations (coupled thermos-mechanical calculation).
The structure is meshed in Finite
Elements either with shell type elements (2D elements) or with brick
elements (3D elements: tetrahedral, prisms, hexahedral). The usage
of these elements allows considering conduction in and displacements
of structures due to pressure and temperature of fluid even for very
complex geometries.
As far as fluid is concerned,
convection and radiation are treated with one of the Finite Volume
schemes chosen according to the flow type: compressible,
incompressible, reactive, etc…
The Finite Volume mesh in contact
with the structures is also auto-adaptive to follow the structural
displacement (strong coupling) and therefore gives a very accurate
calculation of convective exchange coefficient in the boundary
layers at any time.
The radiation is modeled for:
- Transparent media: 3D view factors are automatically
calculated while considering the shadow effect of all intermediate
obstacles.
- Semi-transparent media: Fast and simple models as six
flux model are more complex and accurate as discrete ordinate
Model.
TRANSIENT
SIMULATIONS
The coupled simulation uses two methods,
Finite Elements and Finite Volumes in parallel. Therefore, the user
does not have to worry about transferring of boundary conditions
from a Finite Elements software to a software of fluid flow in
Finite Volumes. This gives accurate answers instead of
approximations in addition to the consumption of time. The time
steps for advancing simulation are chosen automatically for both
fluids and structures by the software.
MODELING WITH fluidyn MP CHT
The architecture of the software and
its CFD mesh generator (fluidyn
CADGEN) is organized in such a way that, they not only
allow the creation of geometries and 3D grids but also to accept
IGES files or input data files coming from other softwares.
An easy-to-use graphical user
interface allows the user to choose the appropriate numerical scheme
and mathematical algorithm among various available CFD solvers. The
code also allows the user to introduce his own equations of state or
boundary conditions through externally compiled software modules.
Thus a user-developed software in FE or FV can also be coupled if
necessary.
As every simulation exercise carries
many assumptions, the user can verify their validity by following
the calculation graphically while it is running. As many as 30
windows can be opened on the monitor screen and various physical
values can be followed simultaneously either as contours, vectors or
graphics.
The user can also interrupt the
calculation for further analysis of the results. He can also modify
the mesh, the equations of state, the boundary conditions and the
solver (in some cases) before letting the calculation to proceed
further.
ANALYZING RESULTS:
The
results can also be saved while the calculation is running either at
regular, pre-specified intervals of simulation time or whenever the
user wishes. These results can be visualized graphically using the
independent Graphical User Interface of fluidyn MP CHT
even while the calculation is proceeding. The
graphical results may also be presented as slide show with user
comments. While working on transient phenomena, the software can
also directly produce animation files. It is also possible to work
on these result files further by applying mathematical
functions.
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