Cooling air flow: Backward rather than downward.

[Logic]

Originally Posted by freebeard

A sizable duct would obstruct the driver's vision.

A small, long duct would have excessive skin friction.

Quite so freebeard, so I'm wondering how much of the flow that normally exits under the car would be vacuumed out through the roof vent and what it would do to/for aero and the unwanted lift..?

In a race rally car, where noise and heat are a secondary concern, they could blow the engine exhaust out through specially enlarged A-pillars.
It'd be interesting to know how that would work!?

Is there any freeware, you're aware of that does this kind of simulating?

[freebeard]

https://duckduckgo.com/?q=CFD+freeware&ia=web

It appears to be OpenFOAM/Simworks.

[Piotrsko]

As a minimum, the exhaust area should be at least the size of the intake. Gonna be hard to get that room adjacent to the human area of your typical vehicle

[aerohead]

Originally Posted by Logic

Quite so freebeard, so I'm wondering how much of the flow that normally exits under the car would be vacuumed out through the roof vent and what it would do to/for aero and the unwanted lift..?

In a race rally car, where noise and heat are a secondary concern, they could blow the engine exhaust out through specially enlarged A-pillars.
It'd be interesting to know how that would work!?

Is there any freeware, you're aware of that does this kind of simulating?

The air flowing towards the A-pillars is in an 'favorable' pressure regime, with zero hindrance to attached flow.
If you wanted to 'improve' aerodynamics, you'd place your 'extractor' somewhere in the rear of the vehicle, where it's 'jet' could enhance flow attachment, or dilute the wake.
The last two of the Ford Probe concept cars did this. As did GM's Precept concept. And Ferrari's FXX full-race coupe, with intermittent, forced-air, 'blown' wake.
Remember though that, even if you have full-power exhaust 'thrust', it does you no real good unless your at 250-mph, or above. You need to be in a 'compressible-flow' environment.

[Logic]

Originally Posted by Piotrsko

As a minimum, the exhaust area should be at least the size of the intake. Gonna be hard to get that room adjacent to the human area of your typical vehicle

Yep; for a stock vehicle it'd be too hot, noisy and impractical.

Even the bit of engine compartment air vacuumed out would be hot and noisy and probably require some silencing (foam or felt or ??) before getting to the A-pillar-duct.
Some heat and noise shielding on the A-pillar interior will also probably probably be reqd.

[IsaacCarlson]

I have been hashing this out for years. The front mounted radiator is most commonly used because it uses ram air cooling when moving. No fan required. It's the highest pressure zone on the vehicle, so it makes sense to put it there. The problem with that is the hot air has to go somewhere. It doesn't matter where it goes, it WILL heat the passenger compartment, either a little or a lot. This puts a higher load on a/c systems and reduces aerodynamics. Long tubes have internal drag, and long skinny tubes have a lot more. It's a ratio of length/diameter.

I started a mid engine project a while ago, and everything penciled out better with the radiator in the rear with inlet ducts behind the rear wheels and on top of the trunk lid. Not exactly what we are discussing here, but it very much applies.

The problem here is it's a front engine car, which makes it one of those things that might be better left alone or lightly modded, rather than trying to come up with something that doesn't really work. Front engine cars are not airflow friendly because all of the heat has to get out, and there is no good way to do that. The hot air usually goes out around the front wheels and under the car.

The best solution is probably an air dam to reduce pressure under the car, and large louvers to direct the heated air backwards out the bottom of the engine compartment. About as simple as it gets without redesigning the entire car. It works and doesn't take much engineering.

Even if you moved the radiator to the rear, you still have lots of engine heat to get rid of.

[aerohead]

I happened to watch NACAR's Daytona 500, with the new 'aero' cars.
Near the end of the race, one of the cars was pushed sideways, became a primitive 'wing' went airborne, and landed on its roof, remaining 'turtle' until the responders could right the car.
The footage provided a really good look at the Mustang race car.
The cooling system's engine bay extractors were located right after the front wheelhouses, with the duct wall radiusing seamlessly into the rocker panels.
The exhaust is completely enclosed above a full belly pan and diffuser, every bit as clean as a Tesla, Lucid Air, Lamborghini, etc..
The 'outgoing' car technology is 'caveman' compared to the new racers.

[Logic]

Originally Posted by IsaacCarlson

...The best solution is probably an air dam to reduce pressure under the car, and large louvers to direct the heated air backwards out the bottom of the engine compartment. About as simple as it gets without redesigning the entire car. It works and doesn't take much engineering...

That's exactly what the linked study in the 1st post said.
With some extra info on the under engine/floor duct sizing.

Then I had the idea to duct SOME of the engine compartment air up to the low pressure area at the front of every car's roof, through the A-pillars.
ie; Vacuum it out via the A-pillars!?

The idea here is to kill 2 birds with 1 stone:
Minimise the amount of hot engine compartment air that normally exhausts out under the car
and
Decrease the lift/vacuum and preferably the drag that exists at the front, top of every car roof.

If you have been looking for ways to minimise the flow of hot engine compartment air out underneath the car, you might put some thought into the idea..?

[aerohead]

Originally Posted by Logic

That's exactly what the linked study in the 1st post said.
With some extra info on the under engine/floor duct sizing.

Then I had the idea to duct SOME of the engine compartment air up to the low pressure area at the front of every car's roof, through the A-pillars.
ie; Vacuum it out via the A-pillars!?

The idea here is to kill 2 birds with 1 stone:
Minimise the amount of hot engine compartment air that normally exhausts out under the car
and
Decrease the lift/vacuum and preferably the drag that exists at the front, top of every car roof.

If you have been looking for ways to minimise the flow of hot engine compartment air out underneath the car, you might put some thought into the idea..?

A look at Professor Alberto Morelli's 1978 CNR P-F concept illustrates one of the most 'scientific' cooling systems ever investigated.
All outlets were wind tunnel tuned at Pininfarina to introduce the engine bay air into their respective boundary layers at exactly the same velocity, so as not to introduce pressure spikes. They spent over $100,000 in tunnel time to dial them in. That would be $400,000 in today's Dollars.

[Logic]

Originally Posted by aerohead

A look at Professor Alberto Morelli's 1978 CNR P-F concept illustrates one of the most 'scientific' cooling systems ever investigated.
All outlets were wind tunnel tuned at Pininfarina to introduce the engine bay air into their respective boundary layers at exactly the same velocity, so as not to introduce pressure spikes. They spent over $100,000 in tunnel time to dial them in. That would be $400,000 in today's Dollars.

Thx
https://iris.polito.it/retrieve/hand..._postprint.pdf

https://www.retro-speed.co.uk/showfeature.asp?art=27302

But no mention of engine compartment ventilation or radiator ducts etc.

I assume there may have been some Meredith Effect?
https://en.wikipedia.org/wiki/Meredith_effect