Exhaust Blown Floor - Forward Exhaust Exit

[Sobek]

I've been lurking for quite a while now, but it seems nobody addressed what has been intriguing me recently.

What impact will the FEE have on car handling during fast corners/turns?
I would imagine that with increasing yaw the flow of exhaust gases will blow at different parts of bodywork, floor and diffuser.

Could FEE bring additional benefit?

[kilcoo316]

Ah ok, yes, as you put it there I agree with you - they are diverting high pressure away from the sidepod onto themselves.

But I still maintain that increasing the mass flow under the floor will lead to increased floor performance. I've been developing T-tray and bboard devices for many years both in CFD and in the tunnel and I trust my results (and so does my boss!).

Indeed.

Air hitting a bargeboard goes one of 3 ways:

1. Longitudinal... in which case it goes around the sidepod, either inside/over/outside the wheel and potentially over the diffuser (inside the wheel).

2. Up... It spills over the bargeboard, some of it going into the radiator - the extra small scale turbulence will help with local heat transfer coefficients on the radiator surfaces and some of it going around the sidepod (see pt 1 for what happens it).

3. Down... which sends it under the floor.

Now, obviously the degree to which 1, 2 and 3 happen is a function of both the bargeboard height, and the bargeboard angle of incidence to the flow. Traditional design has a taller bargeboard height inboard, and much shorter height outboard; reason - to send more air under the floor nearer the car centreline - where it is more effective and will induce less leakage. Kinda analogous to an elliptical wing planform.



The bargeboard exists to control the spanwise distribution of fluid (in terms of massflow or volume flow rate I guess would be the best way to consider it) under the floor, with the bias of flow being weighted toward the centreline.

[kilcoo316]

I also think many people on this thread are getting somewhat confused between static pressure and total pressure.


Pt/Ps = [1 + ((gamma-1)/2)*Mach^2]^(gamma/(gamma-1))




If a nozzle or duct or whatever is subsonic, then its static pressure is equal to ambient.


Total pressure is still a function of the angle of incidence of any surface to the velocity vector of the air impinging that surface (ok, inviscid, but it kinda "loosely" applies for the discussion here).

Cp = 1 - 4 sin^2(theta)

[kilcoo316]

Oh, and the Renault exhausts are there to generate a little bit of downforce from the front sidepod "horns" and to seal the floor much more effectively than standard treatments.

Some of the flow may be induced back over the diffuser, some of it may be induced to treat the tyre squirt SLC mentions... but the majority of its focus is on sealing that floor.

[kilcoo316]

What impact will the FEE have on car handling during fast corners/turns?

Ha.


Good luck guessing that one. It may help prevent starvation of the shadowed side of the diffuser upper deck, but... that is a lot of guessing on my part.

[kilcoo316]

Here is a question... it would probably need an answer from those that have seen some modern DMUs of F1 cars... (or physically the cars themselves).


How easy would it be to retrofit this exhaust to a car not designed for it? Does the tub have to change and aren't they now homogated?

[manchild]

There is one clear advantage - no one will dare to drive parallel with R31 and risk tyre being hit by 600 degrees fumes from not more than 500 mm distance, or sidepods being fed with them - especially in slow corners!

[PlatinumZealot]

[BreezyRacer]

Oh, and the Renault exhausts are there to generate a little bit of downforce from the front sidepod "horns" and to seal the floor much more effectively than standard treatments.

Some of the flow may be induced back over the diffuser, some of it may be induced to treat the tyre squirt SLC mentions... but the majority of its focus is on sealing that floor.

So could one deduce from that that reducing the underbody airflow is desirable then ??????

[manchild]

So could one deduce from that that reducing the underbody airflow is desirable then ??????

No fight, just opinion. If designer didn't want as much as airflow as possible, that they'd put the nose and front of the tub down like in the 80s/early 90s.

[hecti]

So I wanted to post this since we discovered the new exhaust because it reminded me of this car:
http://volvoautosinfo.com/wp-content/up ... aren-2.jpg
Yes, a Mclaren SLR, exhaust exits on the side were said to help the aerodynamics as they helped push the turbulence caused by the tires and wheel wells away from the under floor of the car.

[xpensive]

I also think many people on this thread are getting somewhat confused between static pressure and total pressure.

Pt/Ps = [1 + ((gamma-1)/2)*Mach^2]^(gamma/(gamma-1))

If a nozzle or duct or whatever is subsonic, then its static pressure is equal to ambient.
...

It's been a while kilcoo, hasn't it?

Don't really know xactly where you are going with the above, but I think Bernoulli is quite enough to xplain the different downforce phenomenas on an F1 vehicle, where the following usually works;

If you behold an air-stream horizontally separated by an object such as a wing-profile, or an F1 car for that matter:

Total pressure-pt, is static pressure-ps plus dynamic pressure-pd. Then if total pressure is held constant:
ps1 + pd1 = ps2 + pd2
The above gives a static pressure differential, ps1 - ps2 (which creates Force), equal to pd2 - pd1.

When pd is Density * Speed squared / 2 and Force is static pressure differential times Area, resulting Up- or Downforce becomes:

Area * Density * (speed2^2 - speed1^2)/2.

In other words, everything you do around the floor is aiming at increasing the air-speed under, in relation to over, the car.

What I find interesting here, is what happens with the density under the car with an xhaust contraption such as Renault's?

Think about it.

[kilcoo316]

So could one deduce from that that reducing the underbody airflow is desirable then ??????

No.

But reducing lateral entrainment is very desirable.


The diffuser can (optimally) handle X kg/s (edit: X m^3/s) of air.... you want that X kg/s (edit: m^3/s) to come from the front of the floor, not the side, so the negative Cp it's acceleration induces acts over a greater proportion of the floor.


I guess your work was with airflows > X... (?) So you found reducing towards X increased efficiency.


edit: A diffuser is actually volumetric flow rate limited, not massflow.

[kilcoo316]

Don't really know xactly where you are going with the above,

It might help some people's confusion with underexpanded/overexpanded and fully expanded nozzles.

but I think Bernoulli is quite enough to xplain the different downforce phenomenas on an F1 vehicle, where the following usually works;

Indeed. (Although some localised flow will undoubtedly be greater than Mach 0.3. But the basic principle applies.)

What I find interesting here, is what happens with the density under the car with an xhaust contraption such as Renault's?

Think about it.

rho = P/RT.

T goes up, P is constant and rho thus goes down. That means higher volumetric flow rates for an equivalent massflow rate = greater speeds = better dynamic pressures.

But - (to contradict myself in the post above) the diffuser will actually be limited by volume, not massflow. [I'll go edit that now!]

[vinuneuro]

Just a quick thought. I remember a while back a rumour on this board that McLaren's MP4-26 had side pod inlets shaped like an upside down L. That could be explained if they wanted to supply cooling air to the outside of the exhausts as they route through the car...

Ok since this turned out to be true, any links to the original post?