Dear All
is there any one who performed mode shape analysis via Laser vibrometry to guide me on how to analyze for mode shape of Bladed disk in rotation. the manual did not help much, I used to use it just for velocity or displacement measurement.
How many point do I need? and how I make it correct for a twisted blade?
the attached picture show what I am looking for.
I appreciate it if someone can help.
The manual is quite clear, but it gives (almost) for granted the user be familiar with the physical principles of laser vibrometry. In my case, I had to use the rotational laser vibrometer from Polytec to measure shaft torsional vibrations. Although the rotational speed was measured precisely (within 2% compared to a laser tachometer reading on a zebra tape), i had big doubts that the angular velocity vibration was captured correctly. The signal FFT appeared harmonically distorted and had huge "runout" components that, as far as i know, should have not been there. I tried to compensate for this "glitch" by taking samples at low speed, but unfortunately was unsuccessful. I believe if the surfaces are not prepared in a perfect, lab-style way, you might end up facing similar issues. The distance, the rotor material and the light conditions do seem to play a significant part, but for that i think it´s wise sticking to the user´s manual.
You can write me in private, if you wish/need.
Best regards
Maurizio Sciancalepore
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