Automotive Aerodynamics

Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid in this case. For some classes of racing vehicles, it may also be important to produce downforce to improve traction and thus cornering abilities.

Rail Body Car

Front Axle

Rear Axle

Washer

Tires

Hub Cap and Inner Wheel

Co2 Cartridge

The Car Assembled

Final Assembled Car with Decals

Drawing Of Rail Car

Simulation 2

Simulation 1

First Design

Construction

The construction of the CO₂ car began with a spline-based sketch that was extruded to create the main body. Several critical features were then incorporated into the design. For propulsion and assembly, a canister housing and axle holes were added. To enhance aerodynamic performance, vortex generators were placed on the car's underside. Finally, fillets were applied to the axle holes to reduce stress concentrations at these key points.

The preliminary design for the CO₂ car was rejected due to poor aerodynamic performance. Analysis from flow simulations revealed that the design generated excessive drag and lift, failing to meet key performance criteria. Detailed results from this simulation are available for review below.

Second Design

The design of the second CO₂ car follows established aerodynamic principles, incorporating a low-profile, streamlined body. A key objective was to minimize the frontal surface area—the dominant component of pressure drag. This was achieved through a narrow body and a cone designed to pierce the air efficiently. Certain features like an extrusion on the top of the vechile ensures optimal performance while strictly adhering to all project-specific dimensional constraints.

Analysis of the flow simulation data indicates a substantial enhancement in the aerodynamic efficiency of the second CO₂ car prototype. This advancement is largely attributed to the redesigned nose cone, which has demonstrated a clear benefit in drag reduction when compared to the first design. Subsequent design iterations will target further decreases in the vehicle's overall drag coefficient. The data of the drag coefficient and the lift are below.

Redesign

Aerodynamic redesigns included adding fillets to smooth airflow over the car's edges and installing a vent to optimize underbody airflow. A 7-degree diffuser was also cut into the rear underbody, allowing low-pressure air from underneath to smoothly rejoin high-pressure air from above, thereby reducing rear-end drag. Data below from a flow simulator concur with this statement.

Final Product/Slice for 3D Printing

Drawing Template

The .STL model file was processed using PrusaSlicer. This software converts the 3D design into G-code—the specific instructions the 3D printer follows to build the object layer by layer.

Race Day

The day finally arrived to race the car. Overall, its performance was mediocre, but the experience highlighted areas for improvements. Design changes in the future would include shortening the length, as well as swapping the heavy ball bearing wheels for a plastic; traditional wheel.

Side (Height)

Front

Rear

Race 1

Race one ended with a win. The time achieved for traveling 60 ft was 1.392 seconds. This equates to the maximum velocity achieved by the car to be 48.18 mph.

Race 2

The second race ended in a loss. The time achieved was faster than the previous race. The finishing time was 1.234 seconds. When solving for maximum velocity, the result is approximately 54.27 miles per hour.

Race 3

The Third Race ended in a loss, with the time being 1.203 seconds, traveling 60 feet. Plugging this into the velocity formula used it equates to 55.84 mph.

Conclusion

In conclusion, there is multiple design changes that could be implemented for the future, and experiencing the forces of drag was an informational experience. Concluding the unit, the vehicle had an average maximum velocity of 52.75 mph.

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