Aerodynamic Optimization of a Formula SAE Body Paul G. Kirchner and Dr. Gary Mead Department of Automotive Engineering Technology, Minnesota State University– Mankato REFRENCES Cebeci, Tuncer, and J Cousteix. Modeling And Computaon of Boundary-layer Flows: Laminar, Turbulent And Tran- sional Boundary Layers In Incompressible And Compressible Flows. 2nd rev. and extended ed. Long Beach, Ca- lif.: Horizons Publishing , 2005. Cooper, K. R. Bertenyi, T. Dul, G. Syms, J. Sovran, G. The Aerodynamic Performance of Automove Underbody Diffusers, SAE 980030, 1998 Katz, Joseph. Race Car Aerodynamics: Designing for Speed. Cambridge, MA, USA: R. Bentley, 1995. ACKNOWLEDMENTS I would like to thank the Northstar STEM Alliance for their funding contribuon. I would also like to proudly thank Dr. Bruce Jones, Dr. Gary Mead, Dr. Jeffrey Doom, Kevin Schull, and Winston Sealy for all their help and support throughout this project. OBJECTIVES To analyze fluid dynamics turbulence models accuracy in calculang qualitave and quan- tave data. To understand the significance sidepod size and geometry play in engine heat manage- ment. To understand the significance diffuser angle, throat posioning, and length play in under- tray performance. To opmize the vehicles undertray and sidepod design to produce the highest obtainable INTRODUCTION Formula SAE is the largest collegiate engineering compeon in the naon organized by the So- ciety of Automove Engineers. The compeon challenges engineering programs from around the world to design and manufacture a small Formula-style race-car. The design process in- cludes all components of the automove industry, including research, development, markeng, and financial management. For the 2012 compeon in an effort to increase cornering speeds and cooling system reliability, MSU-Mankato’s body was aerodynamically analyzed using com- putaonal fluid dynamics. The sidepod which houses the vehicles radiator, was altered focusing mainly on the effects of inlet size, length and shroud geometry. An undertray, which mount to the vehicles underbody, was designed ulizing diffusers to increase downforce, the vercal load provided by aerodynamic forces, as opposed to mass. The diffuser secons were simulat- ed focusing on the effects of inlet area, ramp angle, and length. Figure 1. Final CAD model of MSU–Mankato’s 2012 Formula SAE Car. METHODS Figure 2. Engineering Laboratory Design 402 Wind Tunnel Figure 3. Front half of 1/8 scale model for validaon CD-Adapco’s Star+CCM Computaonal Fluid Dynamic soſtware, with internal mesh gen- eraon Due to the complexity of a Formula SAE cars geometry, inial simulaons were run using a simplified bluff body, and symmetry plane implemented along the vehicles centerline to minimize the computaonal fluid domain. All inial simulaons were run with an inlet velocity set to 35 mph, the average speed of a Formula SAE vehicle during an endurance run. Wind tunnel validaon using ELD’s model 402 wind tunnel. Helium Bubble Generator for flow visualizaon validaon. Sidepod A Sidepod B Sidepod C Inlet Size (in) 8.45 in x 11 in 8.45 in x 15.25 in 11.5 in 18.5 in Inlet Area (in^2) 93.6 in^2 120.3 in^2 170 in^2 Inlet/Rad (%) 80% 100% 145% Flow Rate (kg/s) 0.5438 0.5817 0.644 Drag Force (lbf) 4.74 5.22 6.6 Liſt Force (lbf) 0.165 0.14 0.498 Each sidepod was inially analyzed alone to ensure a maximum cell count of 500,000 cells to keep the simulaon within the computers computaonal limits. The sidepod’s inlet area was altered between 80% and 145% of the radiator core size to analyze the effects the turbulent air behind the wheel has on the quality of air the radiator is receiving. The pressure drop across the radiator was calculated using experimentally derived data, from which a 4th order polynomial as a funcon of velocity was derived. Using this data α and β coeffi- cients were calculated and set for a porous baffle interface Eq. 1 (1) A polynomial was fit for the fan using the manufacturer given flow rates and pres- sures, this fan curve was then set for a fan interface within the simulaon. Eq. 2 (2) Figure 4. Streamlines with velocity profile provide simulated flow visualizaon. Figure 5. Pressure contour of undertray, showing center of pressure. RESULTS Table 1. Size, flow rate, drag force, and liſt force from 3 sidepod designs. Using previous research from several sources as a starng point, mulple undertrays were designed varying the diffuser angle from 10° to 16°. The center of pressure was set at the vehicles center of gravity in the for-aſt posion. (Figure 5) Aſter the inial undertray designs, it was evident that flow separaon occurred near 15°. (Figure 7) Several design changes followed aſter verifying the opmum angle, altering the inlet area 30%, adding vortex generators, and the final addion of a keel nearly doubling the downforce. The final undertray has a predicted gain of 49 lbs of downforce, and a decrease of 14 lbs drag. The final design has been rapid prototyped using fused deposion modeling. The 1/8 scale model will be used for wind tunnel validaon, as well as flow visualizaon validaon using a he- lium bubble generator. Figure 9. Final undertray v. no undertray downforce plot Figure 8. Streamline and pressure contour on final body. Figure 6. Downforce per diffuser angle. Figure 7. Drag force per diffuser angle