2012 Exhaust Blowing & Coanda

[hardingfv32]

This is not a sport or a competition, it is a discussion.

It is a discussion, so put something on the table to discuss. Challenge n smikle's work.

The flow drops from about 210 m/s to less than 30 m/s in about 150 mm. So in the case of RB, with their greater distance, it is not to much to expect that the velocity will drop to 15 m/s.

Brian

[Adrian Newby]

Can you not read? The rest of this forum is not required to "challenge" anything, or make up numbers and try to prove they are accurate just because you did. The margin of error in the numbers you are throwing around is astronomical. There is no point in having two sets of such numbers.

[hardingfv32]

The margin of error in the numbers you are throwing around is astronomical.

I think I can ask for some kind of demonstration that my numbers are 'astronomically' in error. 'Astronomical' implies it should easy.

We could all learn something from a good 'discussion' of relevant data.

Brian

[Adrian Newby]

[wesley123]

I think I can ask for some kind of demonstration that my numbers are 'astronomically' in error. 'Astronomical' implies it should easy.

Might be nice to the others who 'discuss' with you to by yourself demonstrate why your numbers are right

[hardingfv32]

Might be nice to the others who 'discuss' with you to by yourself demonstrate why your numbers are right

I am basing my discussion completely on n smikle illustration. I have not ever found any other source for this type of information. I could not prove or disprove n smikle's work if I wanted to. So you guys have as much information as I have.

Brian

[kilcoo316]

General comment>>

You'd be surprised at the exhaust gas speed from an F1 engine.


Based on an exhaust exit temperature of 850 degC and a 75mm dia exhaust nozzle, the velocities will be (approx):


16,000 rpm: 71 m/s
18,000 rpm: 79 m/s


Occasionally, the driver will go as low as 12,000rpm (53 m/s) on braking or 14,000 rpm (62 m/s) on feathered throttle.


In mph, that is:

53 m/s = 119 mph
62 m/s = 139 mph
71 m/s = 159 mph
79 m/s = 177 mph


So your exhaust flowfield isn't that powerful in comparison to ambient - especially when you consider the rapid cooling it will undergo when introduced to ambient (cooler = higher density = slower speed).


The exhaust certainly isn't approaching underexpanded or anything like it.


[oh, and feel free to check the numbers - wouldn't be the first time I screwed up a simple calc!]

[TheWiseOwl]

General comment>>

You'd be surprised at the exhaust gas speed from an F1 engine.

Do you mind putting up the whole calculation?

[kilcoo316]

Do you mind putting up the whole calculation?

Ach feck.

I think I've done this screw-up before.

An exhaust stroke is once every 2 revs, not once in 4!


So calc (including revised numbers)

Bank = 1.2 Litres
Revs = 18000 rpm (=300 rev/sec)

Exhausted cylinder vol per sec = 180 litres/sec

Ambient temp = 288.15K (15degC)
Exhaust exit temp = 1123.15 K (850degC)

rhoAMBIENT/rhoEXHAUST = 0.257

Exhaust exit vol = 7016 litres/sec = 0.7016 m3/sec

Exhaust exit dia = 0.075m
Exhaust exit area = 0.004418 m2

V = 159 m/s



Revising those earlier numbers:

16,000 rpm: 141 m/s
18,000 rpm: 159 m/s


Occasionally, the driver will go as low as 12,000rpm (106 m/s) on braking or 14,000 rpm (124 m/s) on feathered throttle.

[dren]

Ok I will check it out.

I made a small mistake on the reading. There was a small trip in the flow during the iterations and the progam left the max value displayed.

I did a surface parameter check and the velocity at the exit pipe is 209 meters per second.

These are some parameters at the exhaust pipe.

Notice I used the mass flow rate as the input.. because Williams gave a "Normal Liters per second" of air of 450 for the whole engine. I can't use this value as the output of the exhaust pipe.

Calculated results on the exhaust tip.


Mass Flow rate = 0.27 kg/s (I chose this value as the mass flow rate going though one bank of the engine at normal room temp and pressure conditions).

Area = .00593 m^2
Mass Flow Rate [kg/s] 0.27
Pressure: 1.0067 bar
Density: 0.292 kg/m^3 (at normal conditions this is 1.225 kg/m3)
Velocity = 209.74 m/s
Mac number = 0.31
Temperature = 926*C (I think this is fluid reheating)

Volume flow rate: 0.924 m^3/second

Notice that the volume flow rate is much much higher than the 0.225 m^3 per second at normal conditions due to gas expansion.

How much does the fuel add to the mass flow rate? Is it negligible?

[Ian P.]

How much does the fuel add to the mass flow rate? Is it negligible?

Fuel flow is on the order of 150 kg/Hr.
Amounts to about 7% of the total mass flow.
Not negligable, just a minor variation.

[TheWiseOwl]

Do you mind putting up the whole calculation?

Ach feck.

I think I've done this screw-up before.

....

Really interesting! (I have no idea if it's right or not, but 355mph seems a reasonable value)

Is the 'Exhausted cylinder vol per sec' a known value or approximated?

I see how it could be (bank volume)*(rev/s)/2 but does this take into account the increased volume of the combustion gases exiting the cylinder relative the air and fuel entering it?

[kilcoo316]

Is the 'Exhausted cylinder vol per sec' a known value or approximated?

Its geometric.

2.4 litre four stroke engine doing 18,000 rpm

That can only be 180 litres from each bank (2 separate exhausts).

[TheWiseOwl]

Is the 'Exhausted cylinder vol per sec' a known value or approximated?

Its geometric.

2.4 litre four stroke engine doing 18,000 rpm

That can only be 180 litres from each bank (2 separate exhausts).

Yep I managed to gather that eventually (see edit of above post), but still I don't think it's that clear cut.

[PhillipM]

It's not, at peak power rpms I'd expect it to be a little more.