||This research presents a detailed study of non-synchronous vibration (NSV) and the
development of an efficient design method for NSV. NSV occurs as a result of the complex
interaction of an aerodynamic instability with blade vibrations. Two NSV design methods
are considered and applied to three test cases: 2-D circular cylinder, 2-D airfoil
cascade tip section of a modern compressor, and 3-D high pressure compressor cascade
that encountered NSV in rig testing. The current industry analysis method is to search
directly for the frequency of the instability using CFD analysis and then compare
it with a fundamental blade mode frequency computed from a structural analysis code.
The main disadvantage of this method is that the blades' motion is not considered
and therefore, the maximum response is assumed to be when the blade natural frequency
and fluid frequency are coincident. An alternate approach, the enforced motion method,
is also presented. In this case, enforced blade motion is used to promote lock-in
of the blade frequency to the fluid natural frequency at a specified critical amplitude
for a range of interblade phase angles (IBPAs). For the IBPAs that are locked-on,
the unsteady modal forces are determined. This mode is acceptable if the equivalent
damping is greater than zero for all IBPAs. A method for blade re-design is also
proposed to determine the maximum blade response by finding the limit cycle oscillation
(LCO) amplitude. It is assumed that outside of the lock-in region is an off-resonant,
low amplitude condition. A significant result of this research is that for all cases
studied herein, the maximum blade response is not at the natural fluid frequency as
is assumed by the direct frequency search approach. This has significant implications
for NSV design analysis because it demonstrates the requirement to include blade motion.
Hence, an enforced motion design method is recommended for industry and the current
approach is of little value.