Nonlinear Flutter in Fan Stator Vanes With Time Dependent Fixity

Abstract

A new mechanism for fan stator vane failure in turbofan engines at high speed and high loading has been identified and reported in this paper. Highly destructive vane failures have been encountered at Honeywell in a development fan with composite stator vanes. Measured data indicated nonlinear high amplitude vibratory response in fan stator vanes on the stall side of the fan map at high speeds. Analysis showed that under certain steady loading, vane fixity at the hub could change, significantly reducing the vane natural frequency. At this lower natural frequency, the vane was found to be aeroelastically unstable, and calculated response exhibited characteristics similar to those observed during failure. An engine test conducted to validate the role of hub fixity in vane failures showed the failure to be a self-excited phenomenon and not driven by an external source of excitation. It was also shown that failures occur in vanes that are not rigidly fixed, validating the role of hub fixity in vane failures. Test results along with analysis confirm the role of time dependent hub fixity leading to the highly destructive flutter responsible for vane failures.