[zese]

Dear all


I have a general question about the validity of transient rotor stator model to perform the exchange of information between runner and stationary regions. I have 10 blades for runner and 13 guid vanes. in addition after runner I have draft tube. to model this geometry inside cfx I just modeled one passage of each (runner and stator) so the pitch angle between runner to draft tube was 36 to 360 degree. when I run the simulation the velocity profiles matched the experimental measurements inside draft tube; however, the frequency had different values (experimental 15Hz and numerical 17Hz).
could it be because of using one passage of each? or the transient rotor stator has limitations to be used?

does anyone know any references which can help me?


best regards,

[ghorrocks]

The frequency of what? How have you measured it?

[Opaque]

It seems you have not understood the impact of the simplifications you have used.

If you model all the stator vanes, the full rotor passages and do not reduce the draft tube, you will get the exact frequencies.

When you reduce either of the 3 components in the model, you do that at expense of something and must account for that somehow. In the case of reducing the number of passages, the initial assumption of the "rotational periodicity reduction" is that the flow is fully periodic in space and time (which is not always true depending on the reduction).

My advice is that you read the "transient blade row" section of the documentation and familiarize yourself with model reduction of transient models for turbomachinery.