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C5 Aero Analysis

Updated: Mar 23, 2019

Over the last year, most energy had been spent bolting on parts that were expected to make the car faster. The logic here was, the internet is always right. So, on goes the coilovers, spherical bearings, and new sway bars. The result was a whopping 2 seconds around Road Atlanta. Not the bang I had hoped for with a whole new suspension setup.

I then figured, maybe aero is the answer. So, on goes a homemade splitter and APR rear wing. The result: 2 seconds around Road Atlanta. Now, gaining 4 seconds at my home track should have been seen as a big win, but was left with a good bit of disappointment. Running a 1:36 with basic aero on used A7 (275s with 12 heat cycles) is not exactly slow, but it's not going to place in TT3, either.

After another disappointing outing in December (which ended in the T5 gravel trap with a broken splitter), I figured it's time to get a bit smarter about my approach to the car. And, since the splitter needed to be rebuilt, we're starting there.

The first go around was a 3" carbon fiber splitter and an APR GTC-300 carbon fiber wing. Why? Because they are made of carbon fiber and that's as far as I got. The wing is deck mounted, and the splitter is attached to the radiator cradle. You can definitely feel them working; braking into 10a was shaved by at least 50 feet, and very little was given up in terms of top speed.

In an effort to improve overall design, and since I don't have access to a wind tunnel, I turned to computational fluid dynamics. Starting with a very simple 3d model of a C5 Z06, a series of tests were run as a baseline, computing lift, drag, and evaluating air flow around the body. [Note: All CAD work was performed in Autodesk Fusion 360, and simulated in SimScale with post-processing in Paraview.]

Testing for the initial set of configurations was performed at 100 MPH. As we can see from the images below (please excuse the labeling, as the sign is flipped for "Lift", and Velocity is in the wrong units), the base body is pretty efficient in terms of velocity; not much change in velocity around the body. However, the front nose design produces a lot of lift. Additionally, flow over the top produces lots of lift. Overall, the base body, at stock ride height, produced an estimated 324 lbs of lift, and 564 lbs of drag at 100 MPH.

 Further visual analysis of drag shows a lot of drag effect off the rear, in addition to the expected drag at the nose.

Starting from this baseline analysis, we can now iterate through configurations, starting with a full splitter, then rear wing, and finally adding features such as enhanced end plates, canards, etc.

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