Verify that blade packet mode resonance is safe

Published on: 

There are many steam turbine rotor stages with blades connected together for added reliability, making them much more difficult to excite from alternating forces such as upstream vane wakes and potential flow effects such as partial admission. Procedures are described to be sure a "safe" design considers variations giving mistuned resonant response factors.


Compressor and turbine cantilevered blade mistuning effects on response are described in numerous publications. Mistuning can help in reducing response from flutter (negative aerodynamic damping), but can increase response by a large amount for forced response at resonance. Figures below from Reference 1 shows how mistuning affects response at a resonant frequency of a responsive blade mode giving increased individual blade response near the same frequency. For the design shown the tuned 3-diameter mode would not respond from forces if resonant at six times speed, but the mistuned blades would respond.