Bernouli\'s steady flow energy equation
Turbo Mini Forums

Here's something to think about.

Bernouli's steady flow energy equation for compressible fluids:



Basically this says that there are three different components to the energy contained in a compressible fluid or gas at a constant temperature on the move.

The first is pressure as you would measure with the boost gauge.

The second is the velocity energy or kinetic energy. The E=mc2 bit.

The third is due to the elevation and gravitational acceleration.

We can forget the third one as there is little going on in the inlet manifold in terms of change in elevation.

So, the air in port has energy due to pressure and velocity. When that air reaches the cylinder and stops, the energy that was due to velocity doesn't just dissapear because it can't.

What happens is that the velocity energy is converted to pressure energy. So the resultant pressure in the cylinder is higher than the indicated boost pressure.

This is in addition to any "inertia" or "ram" type effects and it is nothing to due with pulse tuning either.

Chew on that :)

Edited by Paul S on 25th Oct, 2010.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Chewing.... But it tastes salty. Will report back later.

Tastes like chicken

Schrödinger's cat - so which one am I ???

Rod, you are correct. Just testing :)

Of course if you measure boost in a large plenum, then this does not apply as much as if you are measuring boost from the inlet manifold.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

monkeying

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Monkeing is abit like aping, a lot more amicaly.
You cannot handle/calc this as easily;

you 've just lighted why the inlet valve need to close later than bdc, their's still energy left in them from their acceleration created by the earlier vaccumed cylinder.

On 23rd Oct, 2010 Paul S said:

On 22nd Oct, 2010 fab said:
monkeying

I think that loosely translates to "ridiculous"

I've just done some calculations and the numbers are so significant that I can hardly believe them.

Rather than make a fool of myself, anyone care to check my calcs by PM?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

i did my own energy equation
right foot over boost wound up + more fuel =more energy and forward motion

Thats about all i understand tbh

I'm just pondering this from first principals, infact now I think about it am I even talking about the same thing? Anway here goes:

Is it this kinetic energy from velocity that creates wave pulses within the port?

For example, inlet charge is flowing at whatever velocity and pressure. The inlet valve slams shut, flowing gas at the on the very back of the valve stops, it has to. Pressure at this point right at the back of the valve rises and a ripple effect/pulse moves up the inlet tract due to more flowing fluid slamming into the stationary fluid and stopping.

Then of course the valve opens and the bugger gets straight into the cylinder to get down and dirty with the pistons etc.

Or maybe the kinetic energy from flow is changed to heat combined with the pressure wave?

No, this is simply the dynamics of the changing state of the internal energy of the inlet charge.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Suppose temperature of inlet charge will have an effect on this?

Everything come back down to the universal gas equation,
pv=mRT
or dynamically, p(v(dot)) = (m(dot))RT

The thing to bear in mind with temperature though is it's measured in degrees Kelvin in physics (and hence the above equations) so apparently large changes when you have a degrees centigrade mindset, are actually quite small.

Schrödinger's cat - so which one am I ???

What the fuck are you talking about? You lost me

I seriously doubt it!

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

good luck to explain these very high ve.. and i will stop there on this subject.

the pressure drop as rev rise is achieved by the restrictor.
these boost pressure are mesured :after carb restrictor, and when you restrict an air flow it'll loose pressure cqfd,
Mesure pressure drop thru the turbo carb/restrictor, then you'll know why I'm competely suspiscious about the mesured numbers.

I'm building the twin set up with pitot tube for a good reason.

If it can help Tdave mesured these years ago:
restrictor is flowing 120cfm,
mety manifold 90cfm.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

So what about the heat? The kinetic energy may very well convert to pressure energy but where you affect one you affect another for the temperature to remain the same whit a decrease in velocity and incread in pressure does not the density have to change or are you suggesting a perfect trade off with pressure and velocity?

Own the day

http://mysite.du.edu/~jcalvert/tech/fluids/bernoul.htm

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Would you agree if i'm using a bit of the brandnew scotch band now???

Andy

They tried to teach me that at uni. So i dropped out.

In boost we trust

The very fact that woodsie was getting well over 200hp eight years ago, using the restrictor, and a T3 turbo, (don't know what he's up to now though) should point that it's a whole different game with boost.
Only reason I did the flow-measurement was to compare the Metro restrictor tube to a plain hole (which as we know never worked out in reality).