Sealing Underfloor with Votices

[mistareno]

I have a sedan based car that I am designing an underfloor for aero setup for. The car is used for Hillclimbs and Sprints so the rules are fairly open.

I was starting the floor with a front splitter. The top of the splitter will be at 0 degrees AOA and the under-splitter surface will taper down on an angle of about 15 degrees to create the underfloor throat. I'm a bit limited to ground clearance as some of the tracks I run on have steep inclines so I'm hoping to start the inlet at about 100mm and have the under car clearance at about 75mm.

I was going to make the downforce generating section about 750mm wide and centrally mounted. It will terminate with a diffuser.

I was going to use continuous length 'spray suppression brush' that trucks use on the guards in an attempt to 'seal' the underfloor along it's longitudinal edges.

The areas between the tunnel and the outer body will still be smoothed, but will not produce downforce. Their only function will be to mount some fences behind the front and rear wheels to guide the high pressure wheel arch air out from under the car.

I have done some reading on wingtip vortices as I thought I could produce a vortice just behind the front wheels and use it to also help seal the floor.

I was intending to mount a small wing tip just behind the front wheels (maybe sticking out 25cm to get out of the boundary air)

I was hoping to generate a wingtip vortice along the length of the car -

Is there a better way to create a controllable vortice?

 

[MikeHalloran]

I'm guessing the trailing edge of the wheelwell could produce a strong vortex, depending on how it transitions into the lower edge of the rocker panel, or the pinch weld flange that's often found there.

Have you studied the aerodynamics of the car as is?
E.g. filming from a chase car or a cantilevered boom camera while driving in rain or snow?



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

To the limited extent of my understanding, aircraft winglets are used to generate some extra lift from a tip vortex that cannot be suppressed.

I.e., the winglets don't generate the vortex, they just try to extract a little benefit to offset the drag associated with the vortex that is unavoidably associated with the wingtip.

I'm thinking that adding a wingtip to the car will add a vortex, but that will also add some drag, so it might be better to try to use a vortex that's already present.

Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

The purpose of winglets is to minimize the formation of tip vortices, which only add drag.

 

[mistareno]

By winglets, I assume you are referring to the up turned wing tips that reduce vortice drag?

I actually need a fairly large vortice to fill the gap between the side skirt and the road (75-80mm)

I figured that with a small wing ending with no endplate, I could angle it down so the tip ends about halfway between the two (road and skirt) and extends out from the car 200mm or so to give the vortice sufficient free air to form?

Drag isn't really a big concern as Hillclimbs are usually at speeds below 160k. The high pressure air that exits the wheel arch would hopefully hit the wing and assist in forming a vortice.

 

[rb1957]

a wing tip vortex is formed due to high pressure on the lower suface "leaking" around the wingtip to "fill-in" the low presusre above the wing.

i think there's so many happening around a car's wheel-well that it's hard to predict how the different components will interact.

why do you think a vortex running down the side of the car will help with hill-climbing ?

i agree drag is not so relevant to you as down force ... so how can you maximise down-force ?

like the brush seal idea ... how about a hovercraft air-filled cushion ?

Quando Omni Flunkus Moritati

 

[MikeHalloran]

Are non propulsion engines allowed?

See 'Sucker Chaparral'.

Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Even assuming that a vortex could be generated, is it going to be doing much at 160 kph?

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[btrueblood]

Mike's suggestion of filming from a chase car is a good one, I'd think. In addition to rain/snow, other methods of flow visualization could also be used - yarn tufts attached to body, smoke from a smoke generator, oil and chalk spread as a film on a flat black painted surface...

As for the wingtip vortex, which way would you like the vortex to rotate? Realize that a lifting wing generates a vortex that rolls "up and in", while a downward-lifting wing generates a vortex rolling outboard and down.