[ghost82]

Hi!
I have a problem with plotting a 2d chart of absorbed power vs time.
I have done my analysis in fluent and I have 200 time steps, time from 0 to 0,1 s.
The simulation is a rotor stator machine, and I want to plot in ensight (10.1.2(a)) the absorbed power of the rotor due to pressure forces.
Here is what I did:

1- Exported absolute pressure from existing fluent files to Ensight format;
2- Placed the point to calculate y moment in 0,0,0 with the tool position;
3- With the calculator, calculated Force(absolute_pressure) on the rotor part: this creates a new Force vector variable;
4- With the calculator, calculated Moment(Force,[Y]); axis of rotation of my rotor is Y; this creates a new constant variable;
5- With the calculator, creation of a new custom variable "Power": Expression is -Moment*Analysis_Time*3036.8729

Power is 2*PI*N*M, where:
N = revolutions/s
M = Y moment, N*m

N in my simulation is a function of time:
N (in revolution/minute) = 3036.8729*Analysis_Time/2/PI*60

So, Power is 2*PI*M*(3036.8729*Analysis_Time/2/PI*60)/60 = M*3036.8729*Analysis_Time

The strange thing is that if I add an annotation for power I can read a value at step 200 (for example) of -24083.26, then if I change to 100 I read power 15369.40 and if I return to step 200 I read 1387.10 (??????).

Values keep changing!

Can you please verify if:

a- My steps to calculate power are correct
b- If there are some bugs in ensight

Thank you and happy holidays!!!!!!!!

Daniele

[ghost82]

I tried to export a few time steps, 10-15, and all seems to work ok..I realized that I had 3 different exported time steps, 197 were 0.0005 s and 3 were 0.0001 s; now I'm re-exporting the files without that 3 time steps, maybe the problems came from there.

[kevincolburn]

Taking a look at the values in the .encas file might yield more information. As you have noticed, there looks to be something odd with the time values (which come from the small ascii .encas file). Double check that the times reported in there are correct, and differ. Time values should always increase, and there should be no duplicates.

If need be, a quick editing of the .encas file may be all that is needed to correct the time values exported out.

-Kevin

[ghost82]

I don't know why, but a reboot fixed my problem and everything it's ok.
If you have some time, can you explain how can I calculate viscous moment to be added to the calculated pressure moment?
Thank you for your prompt support!

[kevincolburn]

There is some information here on calculating the contribution from the viscous side of things, if you are unable to export those values from Fluent. It is an approximation though... so beware.
https://support.ceisoftware.com/hc/e...ons-in-EnSight