Aero track testing

[Jaaps]

Hey everyone,

My team is for the first time starting aero effects on our car this year.

What I'm having trouble with is how to collaborate our results found using CFD with real world track results and since our University doesn't have a wind tunnel it kinda hard to gather 'perfect' data. We are running an unsprung diffuser it wouldn't be worth running linear potentiometer since we won't get any data from it.

I don't know how else we can get pressure/force results especially with a diffuser apart from running the car around a track with and without the diffuser and then seeing track times differences. In doing that I don't think that this method alone would be sufficient to impress the judges at competition.

Any help/suggestions would be greatly appreciated.

Jakob Badenhorst
QUT Motorsport
Aerodynamics Manager

[Jaaps]

Hey everyone,

My team is for the first time starting aero effects on our car this year.

What I'm having trouble with is how to collaborate our results found using CFD with real world track results and since our University doesn't have a wind tunnel it kinda hard to gather 'perfect' data. We are running an unsprung diffuser it wouldn't be worth running linear potentiometer since we won't get any data from it.

I don't know how else we can get pressure/force results especially with a diffuser apart from running the car around a track with and without the diffuser and then seeing track times differences. In doing that I don't think that this method alone would be sufficient to impress the judges at competition.

Any help/suggestions would be greatly appreciated.

Jakob Badenhorst
QUT Motorsport
Aerodynamics Manager

[Mike Cook]

How is your diffuser suspended? Does it secure straight to your hubs or go through your pushrods? In the past we have strain gaged our pushrods to measure downforce.

[mech5496]

Make a trailer-like platform with a couple of wheels, mount the undertray on it using some rods and strain gauges to measure force on each of these...you can figure the setup pretty easily. Then tow it with a car at steady speeds and log the downforce. The moving car will (of course) disturb airflow, but you should be able to have some (rough) numbers. You could avoid some of the turbulence the tow car creates by spacing the trailer by a fair amount from it (dunno if it is safe though). Just my thought on a possible "easy" solution! I would be glad to hear what you came up with at the very end...

[Jaaps]

@Mike: our diffuser is attached straight to our uprights.

@Harry: Yer that could be a quick solution. Kinda after as accurate data measuring as possible, but that is definitely worth a look.

Would there be a way in which we could make a 'pressure map' of the whole diffuser, no idea how we would go about doing it tho.

Thanks guys

[StevenWebb]

One thing you can do, is work out the "effective" downforce by driving in different radius circles with and without the diffuser. It separates all the cfd/windtunnel/BS downforce into the actual "does it make the car faster" downforce.

[mech5496]

Stevens' idea definitely worth looking into, but it requires a full working car AND space to accommodate the undertray under it...if you have both then I would probably look at his way. About "pressure mapping" do as I suggested above, but drill some small holes across the undertray (across the points you want to measure), bond small threaded aluminum inserts on each hole. This will allow you to plug the holes (with a bolt) while not measuring. Now stick some pressure sensors and measure a few points at a time (Pitot or even MAP sensors could do the trick). Time consuming, I know, but I reckon it will do the job...

[Menisk]

So this is kinda (okay, incredibly) dogey and I wouldn't talk about it in design, but could you run stupidly low tyre pressures and watch for sidewall deflection with a GoPro? Get some control data by stacking known weight onto the car and then drive it down drag strip at Willowbank to do some straight line testing. Review the video after to see how much sidewall deflection to get a rough idea of how much force.

[revolutionary]

Some old school tech would be to just run a series of coast down tests to check cd and add to that shock travel sensors to determine downforce.

[Menisk]

They're attached straight to uprights. Won't affect the shocks.