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Supermileage Car Body Design Ivan Monroy Ortiz, Charles Wong, Victor Bobadilla Garcia, Ching Hei Sum Supervisor: Dr. Filippo Salustri Abstract As team captains and team members of the Ryerson Supermileage team, a project to improve on the aerodynamics of the previous Ryerson Supermileage vehicle was undertaken. By integrating theories from fluid mechanics, aerodynamics of road vehicles, and studies of existing benchmark low drag coefficient vehicles in the present day, a series of vehicle body designs were developed under the packaging restrictions set out by the 2010 Ryerson Supermileage vehicle chassis. Iterative testing and fine-tuning of different vehicle body geometries were conducted using SolidWorks’ built-in CosmosFloWorks module for Computational Fluid Dynamics simulation. The final design features a low drag coefficient of 0.08915, which represents a 50.5% improvement in the drag coefficient from the 2007 Ryerson Supermileage vehicle body. plane exhibits a drag coefficient of 0.04, whereas a streamlined half-body at a ground plane will inherit a much higher drag coefficient of 0.15 [1]. A design solution that approximates a streamlined body in air removed from a ground-plane became apparent as the ultimate goal of the project towards the finalization of the design concepts. To aid in addressing the problems of the 2007 Ryerson Supermileage vehicle body, the new 2010 vehicle body was adapted to a tubular chassis to allow more freedom in the design of the underbody. It will also feature a small projected frontal surface area permissible by an ultra-low driver seating position and a vehicle tail that is well tapered to prevent the drag-inducing effect of vortices traditionally developed in the rear of most road vehicles, as well as the high drag force contribution from uneven pressure distribution along the body surfaces. In total, five designs were devised before the final design was chosen. The vehicle height and track width for all designs were kept to be as consistent as possible (with slight variability due to the geometry of the bodies) to allow the design process to be undertaken with a higher emphasis on optimization of the different body geometries. Design #1: Streamlined Half Body Figure 1 2007 Ryerson Supermileage Vehicle Introduction Although fabricated from rigid and lightweight carbon fiber, the body of the Ryerson Supermileage vehicle from 2007 inherited many deficiencies, which greatly negated any benefits gained from the use of this expensive material. Namely, the vehicle body was not well-designed with its 1) large wheel humps, 2) large frontal surface area, 3) rough surface finish, 4) flat underbody 5) and unnecessarily high body thickness. A streamlined body placed in the air far-removed from a ground- The first design was based heavily on the shape of a streamlined half-body placed at the ground-plane. According to literature from [2], the streamlined half-body offset from the ground-plane with the addition of wheels will experience a drag coefficient of 0.15. CFD simulations within CosmosFloWorks revealed a drag coefficient of 0.16681. However, due to the height of the rear wheels, the total vehicle length was increased to 4.22m vs. the original vehicle length of 2.57m for the 2007 Ryerson Supermileage vehicle body to allow the body to properly taper at its tail, which is characteristic of a dramatic increase in body weight due to the requirements for the larger surface area. To accurately recreate the semi-circular frontal surface area while completely enclosing the tires within the body, the projected frontal surface area of the body was an unreasonably large 0.6248m2, which was much larger than the 0.55m2 frontal surface area of the 2007 vehicle body. Design #2 and #3: Lofted Vehicle Body and Lofted Vehicle Body with Tapered Tail For design #2, a lofted vehicle body with smoothly-transitioning body curves was devised. A drag coefficient of 0.12627 resulted from this design despite a larger surface area than design #1, which is likely due to its much lower body length at 3.14m (and hence, lower friction drag), as well as a vehicle underbody that tapers up gently from the ground-plane near the body tail. This allows the pressure gradient between the lower and upper body to be closer in magnitude to each other. In order to reduce the overall length, the taper at the rear of the vehicle was not tapered to a point. In design #3, the addition of a long 1.5m tail to design #2 was implemented to help minimize the flow separation and occurrence of vortices at the tail to a minimum. Results indicated a drag coefficient of 0.11047, which represents a marked improvement over the similarly shaped design #2 in its basic form without the addition of a tapered tail. The improvement in the drag coefficient value was consistent with analysis from literature [3]. wheel fairings integrated into the basic body shape, design #5 inherited a slightly larger frontal surface area of 0.44m2 than design #4, but the flow characteristics were much more favorable due to a simpler surface geometry for the air flow to traverse. Similar to design #4, the upper body was derived from a NACA 64-012 aerofoil due to its superior aerodynamic performance. However, the aerofoil was made larger to fully envelop the front wheels within the basic body shape to reduce the likelihood of vortices forming at the rear of the wheel fairings. The bottom of the vehicle was constructed to follow the curved contours of the tubular chassis as much as possible to better equalize the pressure distribution on the upper and lower surfaces of the vehicle body. Simulations from CosmosFloWorks demonstrated that the airflow characteristics were excellent, with a low amount of flow separation at the tail of the body and the rear of the front wheel fairings. Delta-wing shaped vortex generators modeled accurately based on those from a Mitsubishi Lancer Evolution VIII were implemented fore of the flow separation point at the rear of the front wheel fairings to delay the point at which the flow separates on the vehicle underbody. Design #4: Minimal Frontal Surface Area A minimal frontal surface area was sought in this design concept. By covering the front wheels in low-profile wheel fairings, deriving the upper body shape from a NACA 64-012 aerofoil, and creating a smooth vehicle underbody, this concept featured the lowest projected frontal surface area of all the designs tested at 0.42m2. The drag coefficient was a good 0.13386, and an impressive 0.12507 when the rear wheel fairing’s diffuser angle was set to 3 degrees, which was discussed in literature as an optimal value in reducing the drag coefficient [4]. Unfortunately, the semidetached front wheel fairings were responsible for creating large vortices at near the rear of the fairings, which paved the way for further improvements in the next design. Figure 2 Airflow Trajectories on Final Design The vortex generators were angled (both left/ right) at 15 degrees from the direction of oncoming air for optimum effect in delaying the flow separation point to a location further downstream [5]. Design #5: Final Design Of all the design concepts studied, design #5 featured a drag coefficient of 0.09206 in its basic form, and a drag coefficient of 0.08915 in its improved form with the use of vortex generators near the flow separation point of the front wheel fairings. Owing to the unitized Figure 3 Vortex Generators near Flow Separation Point of Fairing Table Table 1 Results from Different Designs Design Drag Coefficient, Cd Old Design 0.18024 Design 1 0.16681 Design 2 0.12627 Design 3 0.11047 Design 4 with large diffuser angle 0.13386 Design 4 with small diffuser angle(3 degrees) 0.12507 Design 5 0.09206 Design 5 with Vortex Generator 0.08915 IM7 6k yield moderate values of all the AS and IM fibers that were studied, it was strong without being too brittle. IM7 6k fibers can also help to reinforce the frame making the overall vehicle more rigid and to minimize the chassis deflection, giving the carbon fiber a dual purpose, due to its superior strength. The 2010 vehicle body has a total surface area of 6.17m2, whereas the old body from 2007 had a total surface area of 5.94m2. An increase in surface area of the new design was a reasonable compromise that resulted from seating the driver in a much lower driving position. Although a slightly higher surface area resulted from the new design, the fabrication of the body will be contracted out to a 3rd party such that a lower body thickness can be constructed to lower the total weight of the vehicle body to be less than that of the 2007 vehicle body. Succession Planning for Future Competitions Material Considerations Carbon fiber and glass fibers were both studied for their use in the Supermileage body design. The advantages of carbon fiber were its low density, high tensile modulus and strength. Its disadvantages were that the fiber was anisotropic, low strain to failure, and lower compressive strength compared to its tensile strength. The advantages of glass fibers are that they are easily drawn into high-strength fibers from a molten state, and are readily available. Although fiberglass is a lightweight and affordable material, it did not measure up to the superior strengths and moduli of carbon fibers. S Glass fibers had the highest tensile strength of 4.585 GPa. This fiber also had a modulus of 82.737kPa. IM7 6k Carbon fiber was chosen over S glass fiber. This fiber has a tensile strength of 5.310 GPa and a tensile modulus of 276 GPa. To help motivate future members of the Ryerson Supermileage team to advance further in the annual Supermileage competition, and to develop a low drag coefficient body for subsequent use on the Ryerson Supermileage vehicle, a female mold will be used to construct the body. With this method of body fabrication, it is possible to mold multiple copies of the same body design, with the possibility of modifications of body surface geometries integrated into each copy of the body. From an aesthetics point of view, the body also features a sleek and elegant design that is sure to also help motivate future members on the Ryerson Supermileage team to add further fuel-efficiency improvements to the vehicle, allowing Ryerson to develop a solid-footing in the Supermileage competition standings once again in the near future. Conclusions and Recommendations Starting with a basic streamlined body placed near the ground-plane, and transitioning to a lofted body design, and finally to an ultra-low drag coefficient vehicle body design derived from a NACA 64-012 aerofoil, the design of a lower drag and lighter weight was realized. It was determined that the ideal streamlined shapes with low drag coefficients in free air do not perform well when used in their basic configurations for road vehicles. In the end, design #5, which had the lowest drag coefficient, closely resembled a streamlined shape offset from the ground-plane supported by three slim profiles for the wheel fairings. It is predicted that a vehicle body that is even more offset from the ground-plane will exhibit even lower drag coefficients at the expense of a higher vehicle height, and likely, a higher center of gravity. The final design featured many 3D surfaces that were difficult to model in SolidWorks, but its basic body geometry was very smooth. Deltawing shaped vortex generators were used near the flow separation points of the wheel fairings to decrease the drag coefficient on the final vehicle body from 0.09206 (without vortex generators) to 0.08915 (with vortex generators). This represents a 50.5% reduction in the drag coefficient of the 2007 vehicle body, which inherited a drag coefficient of 0.18024. This is a highly impressive result and will be an excellent body for use by the Ryerson Supermileage team for years to come. To further lower the vehicle body’s drag coefficient for future years, it is possible to shorten the chassis’ track width such that the driver is more well encapsulated within the vehicle body, allowing a similar reduction in the body’s projected frontal surface area. Another method of reducing the frontal surface area (and hence, drag coefficient), is by designing a new vehicle without the use of a separate vehicle chassis. Instead, the body will also function as a structural component for placement of chassis components within. In such a design, the vehicle height can be reduced by the height of the current chassis platform (plus any allowances made for tolerances between the body and the chassis). Acknowledgements The team would like to acknowledge Dr. Filippo Salustri for his support throughout the project, the Faculty of Mechanical and Industrial Engineering for the opportunity to provide a platform for designing and competing a full-sized Supermileage vehicle, and the Faculty of Architecture in helping create rapid prototyping scaled models of the final body design. Additionally, the team would like to extend their acknowledgement to Franco Acacia for his continued dedication in helping the team realize the vision in creating a highly streamlined vehicle body for the 2010 Ryerson Supermileage project. References [1] Hucho, W. H. (1987). Aerodynamic of Road Vehicles. Cambridge: University Press. p.202 [2] Hucho, W. H. (1998). Aerodynamics of Road Vehicles (Fourth Edition ed.). United States of America: Society of Automotive Engineers, Inc.p20 [3] Hucho, W. H. (1998). Aerodynamics of Road Vehicles (Fourth Edition ed.). United States of America: Society of Automotive Engineers, Inc.p165. [4] Hucho, W. H. (1987). Aerodynamic of Road Vehicles. Cambridge: University Press. p.143 [5] Hamamoto, N. (2004). Reduction, Research on Aerodynamic Drag. Tokyo: Mitsubishi Motors. p.13.