[Stabum]

Hello, I know that many times people ask in this forum about angular velocity, but still I can't find an answer.
I'm simulating an hydraulic pump that moves water from a reservoir to another one. I need to monitor the hydraulic power (torque*Angular Velocity) during the simulation in order to better interpret the convergence process. To do so I've created the expression Torque:
Abs(torque_z()@hub+torque_z()@blades) and then the expression of the hydro power:
Torque*2*pi*n/60 where n is NOT a variable but the angular velocity expressed in RPM (which I have to update every time I change the impeller velocity!)
Is there a way to express the angular velocity and then the power without manually updating it everytime?

Thanks a lot, really, guys!

[ghorrocks]

What do you mean "manually update it each time?"

Note that is you define n as 60 [rpm] it is not stored as the number 60. It is converted to radians per second, so can be used directly in power calculations. So the power is Torque*n - you don't need to do the conversion from rpm.

[Stabum]

Thanks so much for your reply. With "Manually update it each time" I mean that every time I need to run a new simulation (in which the impeller rotates at a new angular velocity) not only I need to modify the value of the ang. velocity in the rotating domain (pump) but I have to do the same in the "Power" expression. Regarding "n": in my case n is a number, simple, without any unit. In the expression you write (Torque*n) where n is associated to [Rpm] I have to change the value of n as well (update manually the value of n). Is there a way to skip this last action, so that the only change I need to do is update the value of angular velocity in the rotating domain box? Thanks again for the time I make you waste with me.

[ghorrocks]

If you want to add these expressions easily to simulation setup: export it as a CCL snippet. Then import it as a CCL snippet when you set up the run run.

In CFX you should always dimensional quantities (such as a rotational speed) with the appropriate unit. So n should be set to 60 [rpm]. This simplifies the mathematics as all the unit conversions are done by CFX, makes the code much easier to debug. In complex simulations there can be many units conversions, so getting this done by CFX behind the scenes is very useful

It also has the great benefit that CFX will flag when the units of an expression are not right. For instance a volume flow rate is [m^3/s], but if you accidentally tried to defined an expression for volume flow rate which evaluates to [m^2/s] CFX will flag this error. This is very useful in setting up simulations - again, especially complex ones.

So I recommend using best practise, even when you don't really need it for simple applications.

[Stabum]

Thanks so much, I will read them very carefully