End plates for rear flip-ups

[CassonWest]

I will be doing a wind tunnel test next month and wanted to test two different types of rear wheel "flip-ups" that stem back from the sidepods. Of course, this is for a much smaller formula car, but I still wish to find out the differences. The first flip-up is basically a smooth curvature in front of the rear tires, while the second set include sloping end plates towards the outside of them. I have noticed the small end plates on F1 cars, but do not know why they extend theirs downward. Is this for flow cleanup beneath the flip-ups? Any help is much appreciated.

Thank you

[wesley123]

I aint sure but i thought it reduces turbulence from the rear wheel

[CassonWest]

Yeah, a potential possibility. Our formula cars operate at much lower speeds, so there may not be much of a difference. Turbulent air coming off the back of our car is not a worry though. This is autocross style racing. Can the turbulent spillage over the edges affect the diffuser at all?

Thanks

[miqi23]

CassonWest, any chance you can post an image of your car or perhaps that region zoomed in? This will make it much easier for everyone to understand what you are trying to test. This way commenting on your design would be much easier.

Thanks.

[Aerodynamicist#1]

If it is what i think you are talking about, the 'flip ups' are probably used to divert the airflow over the rear wheel, so that the wheel does not affect the flow as much. The flip up should give a clean separation of the flow, and hence reduce the profile drag. Also I think effect on diffuser could be very complicated to model. You could try on CFD if u have access but you really need to know what you are doing.

[CassonWest]

Yes Aero, the flip-ups are used to divert the flow over the rear tires. The flow separation should be relatively minimal, but I am just really looking for info telling me whether or not adding small end-plates will change anything. This is a student Formula SAE racecar, so speeds of around 30-40 mph during autocross runs.

[miqi23]

CassonWest, since you are just looking for a simple answer, I would suggest you use the endplates. Since there would be a pressure difference between the top and bottom surfaces of your flip-ups, you will have a vortex resulting in more drag. The endplate will reduce that and the higher pressure build-up on the top surface as a result will give you more rear downforce.

Hope this helps.

[CassonWest]

miqi23, that does help quite a bit. I talked with the person heading our test and he basically said to go for it. If anything it shouldn't worsen our data. Thanks very much for the help.

[PNSD]

I would be very interested to know how the spinning wheel/tyre effects the flow and the would the effect of the vortex really be felt because of it??

[miqi23]

CassonWest, perhaps you may want to try two elements instead of one to avoid flow separation since the incidence on these things can be extreme. Make sure you use an aerofoil profile on the second flap element and for the first element try to introduce some 'scoop' - this will increase the surface area and will give you more down-force.

[Aerodynamicist#1]

Was just reading in Autosport about these new ducts on the renault car. Some of the hot exhaust gas is captured by a duct and diverted to exit over the top of the rear tyre. I heard someone say that this is for heating the tyre, but I agree with Gary Anderson in that it is to reduce the lift effect produced by the rear wheel. It may sound strange unless you have studied aerodynamics, but rotating cylinders (i.e. a tyre) produce lift, because the rotation moves the separation point on the upper half further back and so a pressure gradient is set up producing lift. Maybe you could use some sort of device like this for your racer. Although the only thing i would say is that the design of the duct would need to be done carefully so you don't end up producing a back pressure for the exhaust, which could be bad for the engine side of things.

[Scotracer]

Wheels are the bane of a open-wheeled car designer's life. Currently I'm designing a Formula Student and the aerodynamic effects of the wheels are getting on my nerves. My university doesn't have a wind-tunnel with a rolling road either, to do some testing (and screw CFD).

[CassonWest]

I am with Scotracer here, as we are building a Formula SAE car. Our wind-tunnel test is free though, courtesy of Daimler Trucks (formerly Freightliner).

Aero, unfortunately we don't have the resources or want to do something drastic like that. It may be a good idea to look at, but it's not cost-labor-efficient for us right now. Yes! TIRES ARE BASTARDS! We are fully aware of the effects. Our focus though is drag reduction, and all we are doing is finding a means of smoothing the flow over the rear end. If end-plates organize things, then we will go with them, if not, screw them. I'm designing some as we speak.

If anyone wants to know results, I will be sure to post some in the coming months.

Thanks you guys.

[flynfrog]

Wheels are the bane of a open-wheeled car designer's life. Currently I'm designing a Formula Student and the aerodynamic effects of the wheels are getting on my nerves. My university doesn't have a wind-tunnel with a rolling road either, to do some testing (and screw CFD).

DAQ your car up every strait away is a wind tunnel and you get to drive the car

[Aerodynamicist#1]

Casson, I'm guessing you guys are all mech engineers since ur doing Formula Student! lol The best way to reduce drag as simply as possible is to reduce the frontal area and make sure the rear bodywork sits high, not like a rear wing, as i don't think u guys are allowed it, just for clean flow separation. Also the use of Gurney flaps is essential if there are large flat surfaces of bodywork for the same reason. Also make sure the nose cone has a virtually flawless join with the monocoque bodywork, i.e. no obtuse angles, which i have seen on some formula student cars lol. Also joins etc become less critical the further you go back, and keep it very clean, to avoid tripping the boundary layer and generating turbulent regions of flow. Any more help lemme know Regards.