Hello fellow Stressers!!

Rotating stall forces can be generated by centrifugal compressors. This typically happens because of flow instabilities in the compressor at low flows resulting in excitation at frequencies sub-synchronous to the compressor run speed.

Can we consider this as Transient (Time History) Analysis or Steady State Vibration (Harmonic Analysis). Maybe it's a time history analysis unlike the reciprocating compressor where the forcing function is continuous (steady harmonic analysis).

Please correct any wrong statement I've made.

Cheers!!

At flowrate q1, you might have no vibrations.
At flowrate q2, you might have high frequency vibrations, but the amplitude probably phases in and out. E.G. V ~= sin(x)*sin(10*x).
At flowrate q3, you might have high frequency vibrations, but the amplitude stays constant. E.G. V ~= sin(10*x).
At flowrate q4, the vibrations might completely phase out altogether.

Harmonic analysis will tell you if you'll have problems at q1, q2, q3, or q4, operating ad infinitum. However, you clearly wouldn't use Harmonic on q1 and q4, and I'm not sure offhand if CAESAR natively handles q2 harmonically, but I do know that q3 "should" be case scenario compared to q2, which I know CAESAR can handle.

Transient analysis will tell you if you'll have problems going from q1 through q4.

However, you can't begin discussion of your analysis until someone tells you what's going on with that compressor with any amount of specificity.

Thanks Michael. Actually, I haven't seen any dynamic piping analysis yet related to Centrifugal Compressors during design stage. I have seen pulsation study for Reciprocating Compressors as per API 618. I have seen a torsional study report for centrifugal compressor itself. I have seen through google a case study related to blade passing frequency which causes excitation on the wall of the pipe & ultimately small bore failures, but this one is troubleshooting study and not on design stage.

Your right, someone must tell with specificity what's going on with the compressor as in the of recip compressor/pump, there is an acoustic/mechanical study being performed following the guideline in API 618/674. I don't know if there is a standard for the same.

Any other opinion is highly appreciated. Just correct me any wrong statement I've made..

Warm Regards,