Aerodynamics behind tires (to add a fairing or leave open?)

[COcyclist]

Originally Posted by JockoT

I wouldn't imagine that would be an aid to fuel efficiency.

Exactly. Although a flat belly pan to an upslope of a 4 degree diffuser can reduce drag. I am getting better mpg with this setup on my Golf. On sports cars the diffuser is usually much steeper to create downforce at the expense of extra drag.

[kach22i]

One can suck the car down on the road so much, it would be like adding a thousand pounds, and that's going to cost you some energy and efficiency.

Can a Formula 1 Car Drive Upside Down?
Can a Formula 1 Car Drive Upside Down? | Bleacher Report

There’s some disagreement over how fast an F1 car would need to go to generate the necessary downforce, but it is scientifically sound. So long as a car is producing a force equal to its weight, anyway...............

https://www.youtube.com/watch?v=Hqw0r0kYl0M

[freebeard]

This one's my favorite:



It doesn't really show in the picture but the fences are curved outward the width of the rear tire tread. With a 4% flat roof this would create a divergent duct with minimal downforce.

And the wheelwell turbulence is segregated and thrown out from 'under the bus.'

[jamesqf]

Need to remember that a road car doesn't just have to deal with aerodynamics, in most places it has to handle hydrodynamics and snowodynamics* as well. And tire chains.

*A timely thought, as we got our first mountain snowfall yesterday.

[freebeard]

I'd attach the roof to the chassis and the outer fences, trimmed to a reasonable departure angle, to the rear suspension. I think the open side snowplow shape would shed better than a conventional mudflap.

[aerohead]

Track cars are primarily concerned with cornering.Low drag might help you on the Mulsanne Straight at LeMans,but you need downforce in the curves.
I would never look to track cars for insight into low drag for passenger cars.
For low drag,the wheels and tires must be integrated into the body.You can use fairings to do it,or active suspension to bring them into the body at speed,or some of both.

[mikesheiman]

Granted, something like having a virtually non-existent wheel well gap on the inside of the front wheel for a standard shaped car (and almost no air gathering behind the front wheel) may be ideal, but

A) How can you fabricate something like that, that eliminates almost all air entering behind the front wheel, around brake lines, the steering rod, the suspension, and other parts?

B) For what air does gather right behind the front wheel, is it actually better to just let it sit there vs. form a vent to drain any air pressure behind the front tire out the side and thus add pressure behind the front tire's low pressure area?


I understand that it's ideal to fair the entire tire separately from the rest of the car body ALA that salt flat car design (option "C"?), but being able to custom-fabricate something like that is honestly beyond me.

[freebeard]

aerohead only posts on the weekends so let me give it a try:

1983 Ford Probe IV Concept - conceptcarz.com

One of Probe IV's most distinctive features are its fully-skirted wheels and tires which utilize membranes between the outer covers and the body. The membranes flex when the front wheels are turned and allow Probe IV to be driven normally, but drastically reduce wheel well turbulence and resulting aero drag.

BMW proposes a morphing skin:

BMW's New Concept Car Features Morphing Skin, Beast Mode. Sorry, Boost Mode.- Core77

[aerohead]

Originally Posted by mikesheiman

Granted, something like having a virtually non-existent wheel well gap on the inside of the front wheel for a standard shaped car (and almost no air gathering behind the front wheel) may be ideal, but

A) How can you fabricate something like that, that eliminates almost all air entering behind the front wheel, around brake lines, the steering rod, the suspension, and other parts?

B) For what air does gather right behind the front wheel, is it actually better to just let it sit there vs. form a vent to drain any air pressure behind the front tire out the side and thus add pressure behind the front tire's low pressure area?


I understand that it's ideal to fair the entire tire separately from the rest of the car body ALA that salt flat car design (option "C"?), but being able to custom-fabricate something like that is honestly beyond me.

A) we'd have to take each car on a case-specific basis.And you wouldn't attempt these details until the rest of the car was 'done.' And you'd have to be REALLY motivated to take this on (bordering on obsession).The lowest drag concepts maintain some degree of the hour-glass openings to allow wheel flop at the front,so it may not be necessary to engineer for closing all of that off.Simulation of a totally-sealed belly in a wind tunnel would indicate if this fruit was worth going after.Tested models from the past indicate that Cd 0.13 is possible without wheel fairings,if this area is sealed.Today's cars use fairings to get the air to 'jump' the opening,then reattach downstream of the opening.
B) Ford's research with the Probe-IV indicated that there's no benefit doing anything behind the front wheels.Not so with the rears.This makes the front a little easier.
For the return trip to DARKO,I'll attempt to mimic a fully-streamlined belly,including full wheel fairings,just to isolate the effect of the hour-glass area.Measurements will tell me if it's worth the effort to pursue a 'streetable' version of the mods.
Get you car down to Cd 0.16,then see if you want to go further.