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-   -   Ask: how to find rpm (http://www.cfd-online.com/Forums/flow-3d/105783-ask-how-find-rpm.html)

hans_ina August 8, 2012 21:52

Ask: how to find rpm
 
Dear All,

Anybody know how to find the rpm (rotation per minute) if i use propeller GMO object which due to fluid flow?

Thank you in advance..

dmilano August 13, 2012 18:15

Look in Analyze->probe->general history->"GMO ... axis angular velocity". The output is in rad/sec.

hans_ina August 14, 2012 01:35

Thank you very much.. :)

saleh alsubari August 14, 2012 05:57

Quote:

Originally Posted by dmilano (Post 376914)
Look in Analyze->probe->general history->"GMO ... axis angular velocity". The output is in rad/sec.

Dear friend
is this in ansys or star-ccm+,cuz my problem is in star-ccm...
thanx for u help

siuseppe August 17, 2012 02:20

Quote:

Originally Posted by dmilano (Post 376914)
Look in Analyze->probe->general history->"GMO ... axis angular velocity". The output is in rad/sec.

How I can find the torque of the GMO? There is in the probe 3 types of torque:
"fluid i-torque about fixed axis"; "fluid torque magnitude about fixed axis" (that is the absolute value of "fluid 1-torque about fixed axis"); "residual i-torque about fixed axis".
Which one is the correct one?

dmilano August 17, 2012 10:47

Component ... GMO fluid x-torque about fixed point: the x component of the fluid torque about the specified rotation point
Component ... GMO fluid torque magnitude about fixed point: the total fluid torque about the specified rotation point (the vector sum of the x, y, and z torques)
Component ... GMO residual x-torque about fixed point: the torque about the specified rotation point that is used to overcome the torque contributions of the inertial forces, body forces, viscous and pressure forces, and specified control forces (or torques) in the x-direction.

siuseppe August 17, 2012 11:31

Quote:

Originally Posted by dmilano (Post 377512)
Component ... GMO fluid x-torque about fixed point: the x component of the fluid torque about the specified rotation point
Component ... GMO fluid torque magnitude about fixed point: the total fluid torque about the specified rotation point (the vector sum of the x, y, and z torques)
Component ... GMO residual x-torque about fixed point: the torque about the specified rotation point that is used to overcome the torque contributions of the inertial forces, body forces, viscous and pressure forces, and specified control forces (or torques) in the x-direction.

Thanks!
obviously I can change "about fixed point" with "about fixed axis", in fact becouse I have to simulate a turbine that rotates around a fixed axis. Correct?

dmilano August 17, 2012 12:14

yep - you are correct

siuseppe August 24, 2012 10:02

I need help!!
In my simulation of a turbine i use gmo couplet motion with fixed axis.
The turbine is made of ABS so the density is very similar to the water.
In the GMO option what method I must use? Implict or esplicit?
Which one is faster for the simulation?

Thanks.

dmilano August 24, 2012 10:12

Use the implicit option in this case

siuseppe August 24, 2012 10:16

Quote:

Originally Posted by dmilano (Post 378557)
Use the implicit option in this case

Thanks!
There is a reason to choose the implicit method, or of experience is the faster?

dmilano August 24, 2012 11:23

I find that it usually just works better

siuseppe August 25, 2012 03:45

ok.
Another question.
In probe output there is the "residual x-torque about fixed axis".
I'm running a coupled simulation with a total torque control in the "moving object setup" tab.
But the "residual x-torque about fixed axis" has always the value of zero.
The only way to obtain a value for "residual x-torque about fixed axis" is to use a prescribed motion with a angular velocity impose to the turbine.

It is correct or I have done something wrong?

In the manual I found that : "Residual control force and torque in both space and body systems for any prescribed motion and a coupled motion with constraints (fixed axis, fixed point and prescribed velocity components)"
It means that if i impose a coupled motion with total torque control, the residual output doesn't appear?

Thanks!

dmilano August 27, 2012 13:38

The residual torque/force is only non-zero in the directions with prescribed or zero velocity components. For example, it may be non-zero in the direction perpendicular to the rotation axis.


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