A study on the effect of exhaust position on drag and lift

[Logic]

Impact of a vehicle exhaust pipe position on the lift and drag coefficients: 2D and 3D simulations
https://www.sciencedirect.com/scienc...40X?via%3Dihub

Maybe i'm just tired or maybe something was lost in translation, but there seem to be contradictions in the text regarding lift and such..?

I'll check again when fully awake, but thought it prudent to leave this here for everyone to read as, it seems my guess elsewhere here was right:
There looks to be a worthwhile drag reduction to be had by placing the exhaust outlet in the middle of a car at speed's rear.

Don't forget that hot exhaust has 4x the volume of cool intake air before whipping out your doubting calculator.
I get 16 000 000 liters per minute for a 2L engine at 8000 rpm.

Vacuuming out the exhausts is also going to help economy.

Another link:
https://www.wrcwings.tech/2022/03/22...rc-rally1-car/

[freebeard]

It's not just you

This pressure difference generates a force that pushes towards the lower pressure contour, leading to a higher negative lift at position 6.
......
The high lift at position 6 is caused by the high velocity air stream coming from the exhaust pipe that travels downwards

Here's a graph that shaded from green/black to blue

Where does the light green come from?

Implicit biases:

The findings of this research could have a significant impact on the performance and efficiency of rear engine vehicles, which are typically the most high-performance and expensive vehicles on the market.

Well, those Type II microbuses are through the roof.

edit: If you see an icon and line break at the beginning of the post, I didn't put them there.

[j-c-c]

Both of my exhausts will exit optimally I hope thru my track cars "blown diffuser", in some ways I hope it is not too effective, as the throttle position will cause quick significant rear DF changes at times not always useful.
We'll see.

[freebeard]

I should redo this pic since I have better software. That said, the one in lower left has a Coanda nozzle:



The Beetle has, by my calculation, 1500CFM of engine cooling air in addition to the [corrosive] exhaust. A 4 into 1 or 4 into 2 into 1 header with a 90 degree elbow would feed into a concave stainless steel box with an insert to make it annular.

For drag, not anti-lift.

[Piotrsko]

Collecting the cooling lift then directing it, or just letting it flow naturally? Collecting it might require cool tin

[aerohead]

Originally Posted by Logic

Impact of a vehicle exhaust pipe position on the lift and drag coefficients: 2D and 3D simulations
https://www.sciencedirect.com/scienc...40X?via%3Dihub

Maybe i'm just tired or maybe something was lost in translation, but there seem to be contradictions in the text regarding lift and such..?

I'll check again when fully awake, but thought it prudent to leave this here for everyone to read as, it seems my guess elsewhere here was right:
There looks to be a worthwhile drag reduction to be had by placing the exhaust outlet in the middle of a car at speed's rear.

Don't forget that hot exhaust has 4x the volume of cool intake air before whipping out your doubting calculator.
I get 16 000 000 liters per minute for a 2L engine at 8000 rpm.

Vacuuming out the exhausts is also going to help economy.

Another link:
https://www.wrcwings.tech/2022/03/22...rc-rally1-car/

After you figure out how to drive without wheels on the car check back with us.

[freebeard]

Collecting the cooling lift then directing it, or just letting it flow naturally? Collecting it might require cool tin

It's been a while, but IIRC the idea was to use the exhaust to pull the cooling air along.

[Piotrsko]

You would think more data is available from homebuilt aircraft: same style of engine cooling and exhaust system, but a cursory search indicates nothing very much new. Couple of radical installations that die after a while or rutans EZ has gone out of favor.

[Logic]

Originally Posted by Piotrsko

You would think more data is available from homebuilt aircraft: same style of engine cooling and exhaust system, but a cursory search indicates nothing very much new. Couple of radical installations that die after a while or rutans EZ has gone out of favor.

I'm not sure how aircraft got involved in this conversation?
They all already have the car equivalent of very long, very aero boat tails, so there's not much vacuum behind them?

The question I asked myself was:

• How much can we reduce the vacuum behind a car
• and
• vacuum the exhaust out the exhaust pipe

by placing the exhaust exit in the optimal, highest vacuum area behind a car at speed..?

Related to that would be the effect of:

• Placing a properly designed Bell Mouth shaped engine air intake at the highest pressure area at the front of a car at speed, to:
• Decrease the high pressure there slightly
• and
• blow air into the engine giving a free (= highest efficiency) turbocharging effect.

Maybe also related:(
The careful shaping and placing of the:

• cooling air intake
• Radiators and other hot bits like the exhaust manifold and engine
• The careful shaping and placing of the now heated cooling air exit

to take advantage of The Meridith Effect: (Thrust from heat)
https://en.wikipedia.org/wiki/Meredith_effect

I NB that The Meredith Effect requires the vehicle to be moving at much higher airspeeds than those of std autimobile travel, but the effect should still mitigate some of the cooling system drag of a vehicle.