A CFD Investigation of Potential Aerodynamic Enhancements to a
Microcar Class Vehicle
by
Jason H. Batchelder
A Thesis Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
in Partial Fulfillment of the
Requirements for the degree of
MASTER OF ENGINEERING IN MECHANICAL ENGINEERING
Approved:
_________________________________________
David Tew, Thesis Adviser
Rensselaer Polytechnic Institute
Troy, New York
May, 2009
1. Proposal
With gas prices on the rise, drivers are personally modifying their cars to improve their
fuel efficiency. Such “ecomodding” of vehicles was also practiced during the gas crisis
of the 1970’s—where Car and Driver modified a Ford Pinto to increase its fuel
efficiency [Sherman].
Furthermore, in the 1930’s, vehicle aerodynamics were
occasionally modified to maximize vehicle speed for low powered race cars such as the
Ford Model T [“Aero Mods”].
In the last few years the ecomodding trend has been accelerating, probably due to a
combination of the increase in gas prices, Global Warming concerns, and the ability to
quickly spread information across the internet. Most of the modifications performed are
done based on the ecomodder’s “common sense”, as well as ideas they pick up from
various sources. Few, if any, of these are based on an analysis of the vehicle, although
many modifications have been verified by drivers monitoring their fuel use over time.
The starting point for many ecomodders are efficient cars, and some of the most
efficient vehicles fall into the Microcar classification.
Currently, the Microcar
classification isn’t strictly defined and varies by country or state, they are typically
around 3m or less in length and only have seating for a driver and a single passenger.
An example available in the United States is the Smart Fortwo.
Although modern vehicles are often designed for efficient aerodynamics, the
popularity of ecomodding means that most, if not all, fuel efficient vehicles will be
modified. With the popularity of Microcars increasing, the question becomes what
efficiency increases are possible for this small and efficient vehicle? It is proposed that
in this project an example of a Microcar is analyzed and various modifications are
investigated to assess their impact on the Aerodynamic drag of the vehicle.
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2. Methodology
A three dimensional model of a vehicle based on a Smart Fortwo was found online<ref>.
The model is a simplified version of a vehicle in that it doesn’t allow any flow in the
engine compartment or passenger compartment, and has a smooth undercarriage which
doesn’t capture the effects of cavities and complex geometry under the vehicle. The
focus of this project will therefore focus on large turbulence generating regions and
separations, such as the back of the vehicle, wheel wells, and protruding features. The
model is meshed using TGrid by Fluent and analyzed at highway speeds using Fluent.
Common modifications performed by ecomodders will then be modeled and analyzed.
This includes, but may not be limited to: smooth wheel covers, covered wheel wells,
side mirror removal, and a modified spoiler.
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3. Timeline
The timeline for the project, including milestone and deadlines is shown below.
January 28
-
Proposal Due
February 2
-
Base Vehicle Analyzed
February 9
-
Mesh Sensitivity Completed
February 16
-
Modification Analyzed (Smooth Wheels)
February 18
-
First Progress Report Due
February 23
-
Modification Analyzed (Closed Wheel wells)
March 2
-
Modification Analyzed (Mirrors and Antenna Removed)
March 9
-
Completion of Analysis of Vehicle Modifications
March 11
-
Second Progress Report Due
April 1
-
Final Draft Due
April 15
-
Final Report Due
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4. References
“Aero mods - 1930's style”, http://www.metrompg.com/posts/model-t-stevinson.htm,
Last checked January 22, 2009
Hoerner, S. F., Fluid-dynamic Drag, Published by the author, 1985
Hucho, W. H., Aerodynamics of Road Vehicles, Fourth Edition, SAE International 1998
Hucho, W.H., Janssen, L.J., and Emmelmann, H.J., “The Optimization of Body Details –
A Method for Reducing the Aerodynamic Drag of Road Vehicles”, SAE Paper
No.760185, p.865-882
Janssen, L.J. and Emmelmann, H.J., “Aerodynamic Improvements – A Great Potential
for Better Fuel Economy”, SAE Paper No.780265, 1978, p.1261-1269
Janudert, “Smart”, 3D Studio Max Model available through 3DVia,
http://www.3dvia.com/jeanudert/models/9337B7899BADBF91, Last checked
January 22, 2009
Katz, Joseph. Race Car Aerodynamics. Bentley Publishers, August 1995
Sherman, Don, “Project Car: ‘Crisis-Fighter’ Pinto”, Car And Driver, March 1974, p.
44-47, 80.
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