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The
Harley-Davidson Motor Company manufactures heavyweight
motorcycles and offers a complete line of motorcycle
parts, accessories, apparel and general merchandise.
These products exemplify a distinct look, sound
and feel which is closely tied to the company°s
heritage. Harley-Davidson is firmly committed to
preserving and enhancing its unique heritage. To
achieve this goal, remain competitive in the market
place, and meet future customer and regulatory
requirements, Harley-Davidson powertrain engineers
incorporate computer aided engineering (CAE) tools
into the product development process. CAE tools
are the key to shorter development time, reduced
development cost, and improved product quality.
Computational fluid dynamics (CFD) is one of the
CAE tools Harley-Davidson powertrain engineers
use to meet these challenges. This article provides
an overview of CFD usage by Harley-Davidson engineers.
The air-cooled V-Twin engine
is the traditional soul of a Harley-Davidson motorcycle.
The use of air-cooling is an integral part of the
vehicle°s character ¬ "the look". With ever increasing
power density, powertrain thermal management is
a challenging task. It is also a very important
part of the product development process. Traditional
empirical methods require testing entire vehicles
either in a wind tunnel or on a test track. Whole
vehicle testing requires considerable expenditures
to prepare and run the experiments. The quality
and quantity of information generated by these
tests is typically limited by instrumentation constraints.
In addition, test track ambient conditions rarely
seem to cooperate with product development schedules.
To reduce costs and improve the final product,
Harley-Davidson engineers use CFD models to address
powertrain thermal management.
Recent publications indicate
that the automotive industry is regularly using
CFD for powertrain (under hood) thermal management.
An air-cooled motorcycle yields unique challenges
not seen by the automotive industry. Consequently,
the first step for Harley-Davidson engineers was
to identify the modeling strategies required to
properly solve these challenges. Figure 1 illustrates
the results of an early investigation into the
meshing and solver parameters required. The particular
example shown is an extruded fin array similar
to those used as heat sinks in the electronic industry.
Figure 2 shows an excellent correlation between
measured and predicted metal temperatures. Comparing
the predicted results to test data provided feedback
regarding the suitability of different modeling
strategies. Lessons learned from such simple exercises
were carried forward into the analysis of more
complicated real world problems. As a result of
this methodical approach, Harley-Davidson engineers
can now analyze engine designs before costly prototypes
are produced.
Thermal management activities
are not limited to air-cooling. The V-Rod motorcycle
represents the fusion of traditional Harley-Davidson
styling with liquid-cooled, contemporary performance
to create a new family of power infused custom
motorcycles. The Revolution engine powering the
V-Rod is Harley-Davidson’s first mass production
water-cooled powertrain. During the development
program, CFD was used to analyze water flow rates
and heat transfer coefficients in the Revolution
engine’s water jackets. Figure 3 illustrates
an example of the results generated during this
project.
The lubricating oil is another
liquid flow system Harley-Davidson engineers use
CFD to evaluate. The pipe flow portion of the lubrication
supply system is modeled using a one-dimensional
(1-D) "network" analysis program. The
1-D program is an efficient tool for evaluating
system operating pressures and flow distributions.
Not all lubrication system components meet the
assumptions made by the 1D program. The flow characteristics
of these components are evaluated using three-dimensional
(3-D) CFD. The results are parameterized for use
by the 1-D code. Although it is possible to couple
the two codes together, Harley-Davidson engineers
have not found a need to use that capability. The
present approach allows rapid evaluation of proposed
designs concepts and changes.
The multi-phase nature of oil
splashing in the crankcase is treated using three-dimensional
CFD. Spray and droplet breakup sub-models are used
to track oil particle generation. The Lagrangian/Eulerian
framework predicts the motion of a dispersed phase
(oil particles) within a continuous phase (air).
Simultaneous solution of the energy equation allows
for heat transfer between the oil and the metal
parts to be evaluated. Moving grid capability (cell
addition and deletion with vertex motion) allows
the motion of the pistons to drive the flow within
the crankcase. Incorporating CFD gives Harley-Davidson
engineer’s the capability to separate and
independently study different aspects of the problem.
This capability was not possible with the traditional
empirical techniques.
Harley-Davidson uses CFD in
the develop-ment of the power cylinder components.
Evaluation of intake and exhaust port flow coefficients
is accomplished without the need to manufacture
costly flow boxes and run time consuming tests.
An automated mesh generator and existing solid
models make the computation of port flow curves
a nearly automated process. Final engine performance
predictions are made by incorporating the port
flow curves into a cycle simulation code. Using
the same techniques, the flow characteristics of
induction and exhaust system components are evaluated.
After static flow comparisons of several designs,
the best areevaluated for engine performance by
coupling the three-dimensional CFD model with a
cycle simulation code. Complete three-dimensional
CFD calculations of the entire power cylinder are
used to evaluate engine performance. These models
combine advanced capabilities such as moving mesh
with fuel spray and combustion sub-models. This
type of analysis provides information regarding
mixture preparation, combustion efficiency, heat
transfer, and emissions formation. Figure 4 presents
a power cylinder model sample result.
Incorporating
CFD into the product development process allows
Harley-Davidson Motor Company engineers to improve
product quality while simultaneously reducing
development time and cost. The resulting products
incorporate advanced technologies while maintaining
the corporate heritage.
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fig 1: Predicted
metal temperatures
for an extruded fin array
fig 2: Comparison of predicted and
measured extruded fin array metal temperatures
fig 3: Predicted
water cooling system flow velocity
fig 4: Predicted
Combustion
Gas Temperature
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