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By Ron Gadoth and Sadek Rahman, DaimlerChrysler, Auburn Hills, MI; Neil Slyva, Flowmaster, Livonia, MI; and Pepi Maksimovic, Fluent Inc.
View the pdf of this article
FLUENTLink is an interface between FLUENT and Flowmaster that
enables engineers to perform co-simulations with these two software
products. Developed by Flowmaster Group, the FLUENTLink
coupling makes it possible to couple a quick 1D simulation in
Flowmaster with a detailed 3D analysis in FLUENT. One popular automotive
application area for co-simulation is engine cooling.
The geometry of the turbo engine, showing the
cooling jacket and water pump (to be simulated
using FLUENT) and remaining components
The FLUENTLink GUI (top),
Flowmaster schematic (left),
engine geometry (right), and
FLUENT boundary condition
panel (bottom) show how the
software codes are coupled
Contours of static pressure and velocity vectors
on selected planes from the FLUENT simulation
Flowmaster is a 1D analysis code used to evaluate the overall performance
of a system of components. Its focus is on system effects
rather than detailed geometric effects. Flowmaster calculates pressures,
flow rate and temperature across the whole system but it cannot
explore the flow and heat transfer inside the component in full, threedimensional
detail. FLUENT, on the other hand, can provide this kind of
detailed information, which is often required to make component level
design modifications. The compute time for a full 3D analysis is substantially
longer than that for 1D codes such as Flowmaster. Thus, while a
1D system analysis may not provide enough information for component
level design decisions, a full 3D analysis on a system level would be
computationally expensive and impractical.
Co-simulation is a concept that combines the strengths of the 1D and
3D approaches. An analysis of the whole system is performed along with
a detailed 3D analysis of an individual component. By automating the
process, the time required for manual data exchange back and forth
between the 1D and 3D calculations can be reduced, and the associated
user input errors can be avoided. The FLUENTLink installation package
consists of three components: a front-end graphical user interface (GUI)
for setting up the problem, pre-compiled user-defined functions (UDFs)
for communication between the FLUENTLink GUI and FLUENT, and an
RPC license for data communication over a network when FLUENT runs
on Unix platforms (since Flowmaster runs on Windows only).
One example where co-simulation has been applied is a turbo
engine cooling system from DaimlerChrysler. The system consists of a
turbo engine, heater core, thermostat, oil cooler, radiator, water pump,
cooling jacket, and connecting hoses (among other components).
These components are represented as parts of a circuit in Flowmaster.
The cooling jacket and water pump, however, both of which involve 3D
flow that is influenced by heat transfer, are modeled using FLUENT. To
set up the coupled simulation, a stand-alone Flowmaster circuit is first
created and then modified by inserting controllers and gauges at the
locations where data sharing is to occur. Boundary configurations are
prescribed in the FLUENTLink GUI by identifying the appropriate zone
ID numbers for data transfer. In FLUENT, UDFs are chosen for the corresponding
inlet and outlet boundary condition variables. The calculation
begins, and stops in FLUENT when the convergence criteria are met.
The results of the coupled simulation for the turbo engine show an
increased flow and/or pressure drop through certain components compared
to an analysis using Flowmaster alone. By providing better
boundary condition information for the FLUENT calculation, more accurate
thermal and flow conditions can be passed back to the Flowmaster
calculation, leading to a quick and economic way of generating better
system performance predictions.
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