Motivation

When I entered Texas A&M as a National Merit Scholar on a prestigious scholarship, I
expected the system to work with me a little. Instead, for two years, I was shut out of every research opportunity I pursued. My advisor eventually admitted, “the system has truly failed you.” That moment defined me. I stopped waiting for permission and started creating my own path.
I built my first research experience myself—entering the McLaren F1 CFD Challenge,
writing my own syllabus of work, and earning a perfect score. That self-motivated mindset led me into Formula SAE, where I went from sanding parts to leading an all-new aerodynamics sub team in less than a year. I shaped the design philosophy, ran simulations, manufactured composite parts with my own hands, and tuned the aerodynamics package to improve overall lap time by over 2 seconds.

Design & Analysis

Three things needed to come first before design: interpretation of the rules/identification of loopholes, justification of why the car needed aero (what does an aero kit do?, F=ma_c, etc.) and a full-team philosophy that provided a shared metric for improvement to the car in the form of reduced lap times.

As lead, I was responsible for setting reasonable goals/requirements. In a new 1-year design cycle team, research was essential to achieving the goal. Initial research targeted information that would help our aerodynamics sub team perform trade studies on components to include on the car. The resulting components selected were a high nose cone, multi-element front wing, undertray/diffuser, multi-element rear wing, and dacron body panels. I then referenced existing research for target C_L and C_D values for this kind of package.

As important as overall downforce is to the car, stability and drivability were core to our design philosophy, so the aerodynamic center of pressure (CoP) location was a target. For stability’s sake, I set a longitudinal CoP aft of the center of gravity (CG) along the car’s centerline. Moreover, from a side-view of the car, the CoP needed to be aft of the CG in order to provide stability from side-winds. Finally, CoP migration needed to be minimized to provide a consistent driver feel/confidence, which was a large reason I opted for an undertray as a centralized aerodynamic device.

The system I had to develop to constantly justify aerodynamic changes was running CFD on designs to find aerodynamic values, then taking those inputs alongside car weight, powertrain, and suspension data to run lap time simulations. Hard to argue with our overall argument of the change making the car faster.

How did I set up simulations? How did I arrive at a target speed? Well, the first iterations of designs were designed with a target speed of 33 mph for cornering a hairpin-like radius as the rules for endurance recommend. Then, I worked with suspension and testing car AIM data to find the average cornering speed of an old track with a real FSAE car and back-calculated the average cornering radius for endurance to use for ‘25. Weighting these by prominence on track provided an average speed of 36 mph, which produced the following results.

Moreover, running a Yamaha R6 engine allowed us to not worry about drag for endurance and autocross (our prioritized events as a full team). Regardless, I did estimate the bhp absorbed by our endurance set up. This was the equation I used from McBeath’s book on Competition Car Downforce:

Working with a teammate, I managed to run simulations for straight-line and sensitivity studies. These sensitivity studies (dynamic conditions: pitch, roll, yaw) were essential as this was the school’s first ever ground effect FSAE IC car. Undertrays are notoriously sensitive to dynamic conditions, so I interfaced a lot with suspension to figure out max roll, pitch, yaw (we even ended up using stiffer springs than we designed for as we got faster lap times).

Overall, simulations were run with a target y+, factoring in our use of wall function because the supercomputer was down, so we had to reduce computational demand. Moreover, I validated our simulation methodology initially using Ahmed Body studies. We did not gain access to a sizeable wind tunnel to thoroughly validate our CFD. So, I modeled the existing Ahmed Body (similar to automotive design) and compared our CFD results to real life existing wind tunnel data for that bluff body. We fell within 7% while being able to run simulations on our laptops and found a happy medium for iteration there. Additionally, I selected k-omega SST turbulence modeling (lots of boundary layers and their interactions).

Though I was responsible for the aero package working well as an ecosystem, I also had to design and manufacture my component: the undertray/diffuser.

Key design points for my undertray:

• Steeper inlet angle than diffuser exit
• Create pressure gradient (high front, low pressure rear) to accelerate air underneath the car
• Bernoulli’s effect
• Maximize diffuser exit length for flow attachment
• Encouraged side-tunnels over purely underbody
• Shorter throat is less sensitive to changes in ride height/dynamic conditions
• Lip/floor edge houses vortex that helps seal the flow of the tunnels
• Rear wing (if you have “beam-wing” style lower elements) can “extend” the diffuser and allow for a higher exit angle while helping keep flow attached and low pressure at the exit
• An open venturi system differs from a quasi-1D tube in the way that it is dominated by vortices. Flow is energized and stays attached through the control of vortices
• Inlet in-board of tire wash
• Do suspension members require fairings?
  • Tufts showed minimal turbulence ahead of the floor
• Strakes help to maintain vortices in corners
• Experimented Diffuser angle 11-13°, 13° had peak downforce and minimal increase in drag

My iterative design involved computationally determining inlet and outlet angles for the diffuser, then slowly modifying the design to perform better in dynamic conditions. The greatest improvement to the design came from introducing more vorticity with strakes. Below are some CFD results to better understand the flow:

Manufacturing

I led almost all layups, tracking durations and procedures through a “layup sheet” on my iPad. This process was helpful in not repeating mistakes and improving on every layup.

For my Undertray:

• 6 layer wet layup (overbuilt – hindsight is 20/20)
  • Conducted bend tests on test pieces of different # layers to determine optimal rigidity
  • Vacuum bag failed to properly cover complex contours
  • 3D-printed, sanded, bondo’d mold
  • A mold was 3D-printed out of ASA to create the 2 diffuser tunnels.
  • 6 layers of 3k carbon weave were then wet laid over the mold and a flat center area.
• Tunnel insides were repaired and finished with flash tape, epoxy, and 2-part clear coat for smooth wetted surfaces
• The underbody was fastened to the chassis using DZUS fasteners (flush, minimal aero impact), and the tunnels required rods to prevent flexing under load.
• Strakes were 3D-printed and attached with adhesive
• Rods used 10-32 bolts with nylock nuts
  • I designed a jig to align and weld the chassis tabs
  • Slot-head bottom bolt to use the same tool to take off DZUS and bolt, removing diffuser fully

Testing

Testing involved a lot of back and forth with suspension to find the optimal ride height for overall vehicle dynamics and underbody performance (lap time trumps all). Moreover, I did not model the suspension rods in our CFD simulations and wanted to check their influence on flow entering the inlet. Thus, I ran some tufting as shown below. At endurance/autocross speeds, our GoPro footage showed no problems in that area.

I also tuned the front wing and rear wing for overall better aero balance and faster lap times. Upwash from the front wing decreases rear wing performance, and this effect grows under braking, leading to a less predictable car. I took driver feedback and lap times to mitigate aerodynamic balance problems.

(We also did some CFD validation with coast down testing and skid pads at varying radii, but the skid pad results were not usable).

Final Notes

There is definitely more depth to a lot of this that I am happy to have conversations about, but I truly could not fit the past year’s worth of work in a portfolio post. More importantly, however, I learned firsthand the difference that a good team makes. I could not have done it without y’all aero boys: Nick, Kevin, Mauri, Liam, and Sid. I remember waking up every morning coughing up blood for 2 months straight, but you guys helped remind me I had a reason to show up (eventually realized my apartment unit had bad mold poisoning). Thank you for a season of memories and delivering when life called on you.