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-   -   Axisymmetric model and 2Pi factor (https://www.cfd-online.com/Forums/siemens/204837-axisymmetric-model-2pi-factor.html)

killian153 August 2, 2018 06:03

Axisymmetric model and 2Pi factor
 
Hello!

I recently asked on the forum if I should mulitply by 2Pi my results on an axysimmetric model of a rocket nozzle.
@fluid23 answered me yes, with this sentence from the user manual "Any volumetric and area quantities reported for the Axisymmetric model are assumed to be for a 1-radian sector. If you want the value of a quantity for the full 360 deg revolution, multiply reported quantities by 2pi."

But I have something weird with this 2Pi factor.. My simulation is based on an existing rocket engine from an amateur guy, which is designed to have 100 lbf of thrust (about 45kg). In my model, I got 520 N of thrust, which is approximately 53 kg. It's quite similar but if I multiply by 2Pi, it becomes 330 kg, which is totally inaccurate.

I set up the right chamber pressure, dimensions etc. so I don't really understand. My thrust report is set on the inlet.

I even tested my model on an other rocket nozzle from him which is supposed to have 250lbf of thrust (113 kg) and I got 111 kg with my model!
So, I think that Star CCM converts automatically the axi value, but I could be wrong.


Thanks!


Killian


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