Hi Paul,

        If your formula & calculations are correct for the 15,000 RPM case where you come up with a centripetal stress of 48 psi; then for a 150,000 RPM case where V is 10 times as large, then V
squared is 100 times as large and the stress increases from 48 psi to 4800 psi which is very close to the extrapolated 5 Ksi strength at 1750 F exhaust temp. That would seem to indicate that if the
conditions allow the turbo to overspeed to the 150,000 RPM range, then a simple fatigue failure is quite likely without the assistance of any exotic resonance conditions.

        Have I overlooked something here?

Cheers...........Gary

Oh right!!! I missed that. I think that is what Dave was trying to tell me. Sorry Dave.
I dropped a zero there.

Well you hit the nail on the on the head Gary. Thanks for checking my work.

I take it back. Over temp and over speed would do it!

Two bad things are happening here. The loads and stress are going up
with the square of turbine RPM and the max stress is on a very slippery
temperature slope indeed.
Paul Lamar

Paul, If these failures are an indication it would seem
that we should use a slightly oversize pressure side to
prevent over-speeding. It would lower the overall efficiency
slightly but might be the saving grace for high altitude use.
Bill Jepson

Yes I agree. That could be one of the techniques.
The effect of excessive centrifugal force seems to be the most important.
I would still like to analyze the blades for resonant conditions.

Paul Lamar
 
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