| By A. Cantagalli and R. Rossi, Laboratorio di Termofluidodinamica Computazionale Seconda Facoltà di
Ingegneria di Forlì, Forlì, Italy; S. Di Piazza and A. Ferraresi, Ducati Motor Holding S.p.A., Bologna, Italy
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Pathlines around
the vehicle
The Computational Thermo-Fluid-
Dynamics Laboratory of the Forlì
School of Engineering and Ducati
Motor Holding have developed an innovative
approach to the analysis of motorcycle
heat exchanger performance.
Called the “numerical multiscale method”,
the approach makes use of different orders
of spatial discretization to analyze two heat
exchangers embedded in the complex
geometry of a motorcycle. The approach,
which has been carried out on the cooling
system of the Ducati 999 motorcycle,
couples FLUENT with an in-house
“distributed parameters” code.
Air-water (top) and air-oil
(bottom) heat exchangers
Heat exchangers represent the main
component of a motorcycle’s cooling system.
Two types are commonly used: air to oil, and air to water. Through these heat exchangers,
the major part of energy produced by the engine’s internal
combustion is released to the environment. The auxiliary
weight and size of these components are considered
drawbacks in terms of performance and efficiency loss.
Thus, there is a need to design heat exchangers that guarantee
maximal heat rejection with reduced overall dimensions.
Usually, the designs are based on the experience
acquired from previous projects and from experimental
data obtained from costly prototyping. Approximate formulae
and correlations for heat exchanger design can
also be used, but they do not help designers achieve a
proper balance between cost and performance.
For the coupled analysis, a FLUENT simulation was first
performed for the entire motorcycle, starting from the
CAD surfaces of the vehicle provided by Ducati. The external
flow analysis provided velocity distributions on the
surfaces of the two heat exchangers. In the FLUENT simulations,
the heat exchangers were modeled by a porous
media in order to simulate the pressure drop across the
components and the deviation experienced by the air when
crossing them. The surface velocities predicted by the CFD
analysis were then used as boundary conditions for the
distributed parameters calculation for the heat exchangers.
This approach uses a formulation that is based on
the discretization of a system with n elements or entities,
each of which represents a part of the system analyzed.
In each of these entities, an integral form of balance equations
is solved. For the heat exchangers, the distributed
parameters calculation provides a detailed temperature
distribution throughout the heat exchanger.
The CFD results illustrated some interesting features
of the flow in the vicinity of the heat exchangers. The
velocity distributions on the heat exchanger surfaces clearly
show the influence of the front fork and front wheel.
The upstream components also give rise to a non-uniform
turbulence intensity on the surfaces of the heat
exchangers, which may influence their operating efficiency.
The full vehicle model solved in FLUENT
The distributed parameter predictions for outlet oil
temperature are in good agreement with experimental
data. The success of the coupled calculations suggests
that the numerical multiscale method is a valuable tool
for quantifying the effects of surface velocity distribution
on heat exchanger performance. It is cost-effective, too,
since the analysis time is considerably less than that of a
full CFD analysis of the motorcycle and heat exchanger
detail for each proposed design change.
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