[killian153]

Hello!

I post this thread on the main CFD forum, since I had no answers in the Siemens one.

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 was wondering : does Star CCM automatically converts the axi value so that a 2Pi factor is not needed ?


Thanks!


Killian

[LuckyTran]

As far as I know, you should multiply by 2pi.


You can confirm this by running the 3D model.

[killian153]

Originally Posted by LuckyTran

As far as I know, you should multiply by 2pi.


You can confirm this by running the 3D model.

Hello!

Sad news for me I guess

By running the 3D model, you mean recreating the nozzle in 3D and set up a new simulation ?

EDIT : indeed, after 3D test, I have 6830N of thrust, which is approximately the result of the axysimmetric, multiplied by 2Pi..

So I don't really understand what is wrong with my simulation..