The pressure is what I am trying to calculate.
Number of nozzles and orifice size.
I can go as high as 1000psi
I've got a V8 motor I can put light springs on the intakes grind down
the exhaust lobes and pump out the spark plug holes if I needed that
much flow.
But I'm pretty sure we can do it with a bottle of dry nitrogen.
-------- Original Message --------
Subject: [AR] Re: Turbopump prime mover
From: Ed LeBouthillier <codemonky@xxxxxxxxxxxxx>
Date: Wed, December 02, 2015 8:34 am
To: arocket@xxxxxxxxxxxxx, arocket@xxxxxxxxxxxxx
Monroe L. King Jr. said:
This turbine is just the prime mover for testing the pump it is HP air
driven.
What pressure?
As you saw, there is an inverse relationship between Isp (Ve) and mass flow
requirements.
If I recall, compressed air has an Isp of about 50 seconds = 1610 fps.
The equation for calculating Ve is here:
https://en.wikipedia.org/wiki/Rocket_engine_nozzle
A turbine can be seen as a rocket (or lots of little rockets) which
drives its gas at its exhaust velocity (Ve) onto the turbine. So the
equations for rockets apply to the gas generating side of the turbine.
You can use propep to calculate the Isp (Ve) of your gas system. But it's
likely to be pretty low (~30s to ~50s).
The problem will be generating enough mass flow to cause choking in the
turbine inlet. You may not see that kind of speed if you don't have the
mass flow.
This wikipage shows the equation for choking:
https://en.wikipedia.org/wiki/Choked_flow
It says that the pressure differential needed to sustain choking
with air is 1.893. Therefore, if the exhaust pressure is 14.7 PSI,
then you need to be able to sustain about 28 PSI at the inlet to
the turbine nozzle.
Once I have a working pump we can then work on a real turbine. :)
Neat.