Hi,

How can you validate a solution using Fluent? I have used the mass flow rate flux to see if the solution is valid. For flow in and flow out the net result is 1.401077e-09kg/s. Should this equal zero or is this an acceptable result? Please advise.

John.

If your flow rates are in the order of magnitude of 1E-8 kg/s then your mass flux error would be too big, 10%. If your flow rates are in the order of magnitude of 1E+8 kg/s then your mass flux report error would be damn small...

I guess anything under 0.1% is good enough. What do you think yourself?

Thanks Erwin,

That makes sense now. Just wasn't thinking earlier. I have no idea what percentage is acceptable. Is it up to the user to decide what level is accceptable or is there some kind of standard?

Erwin,

I just found this in the Fluent 5.5, 2D Centrifugal Blower tutorial, post-processing -

"The net mass imbalance should be no more than a small fraction (say, 0.5%) of the total flux through the system. If a significant imbalance occurs, you should decrease your residual tolerances by at least an order of magnitude and continue iterating".

John

There you go. I usually find that in most problems that I do mass balance is not a big issue, energy balance on the other hand can be tough, especially when radiation is involved.

Cheers Erwin