Learning Forum

[jplopes]

Hi,

I have a 2D axisymmetric swirl model of an unusual turbine, with moving walls but no blades. The domain is just a rectangle. I specify the inlet velocity, the rotational velocity of the walls and zero pressure at the outlet. There seems to be no problem with the solution.

What I'm trying to do now is to calculate the power generated, by getting the torque at a wall and multiplying that by the rotational velocity. I can get the torque via a moment report and the value matches an analytical solution I have:

Now I wanna get the power by creating an expression report using this value -- the product of "wall_torque" with the RPM. However, when I use the "wall_torque" value in another report, it is being outputed as zero, even though the value was correct (and non-zero) before:

I don't know what I'm doing wrong. I have created expression reports from other reports before and it was always fine.

For instance, I have a "pressure_drop" report calculated previously. If I do the same procedure above with it instead of the "wall_torque" report, it works fine:

[Karthik Remella]

That makes no sense. What is even more interesting is that your unit shows up correctly. Could you please run one iteration and check this again?

Thanks.

Karthik

[jplopes]

Nothing changes after running another iteration. I can still get the right torque from the moment report but whenever I try to use that in an expression report it gets set to zero.

I was able to reproduce this behaviour on the "wind turbine blade" CFD model of the Cornell's EdX course. After running the simulation, we get the torque on the blade with a moment report. This gave me the correct result (according to the course). Next, I tried to create an expression report as twice the torque and it gets set to zero as well, so the problem doesn't seem to be in my model.

Expression reports that change velocities, pressures or even forces seem to work, the only problem seems to be with moments.

Thank you for your help, Karthik.

Best,

Jhonatan.

[ericmh]

Is there an option under report definitions to specify how precise you want your decimal values? It seems to be rounding your value to 0.

 

Thanks,

Eric

[Karthik Remella]

Hello Jhonatan,

Excellent catch. I tried to reproduce it at my end and I saw the same issue you are seeing. Let me dig a little deeper and get back to you.

Thank you for your patience.

Karthik