Blade vibration - Some key elements in design verification

From among the many topics in design verification of blade vibration, a crucial aspect of all airbreathing engines' qualification, this paper outlines in some detail two key considerations: 1) the assessment at a given operating point of compressor and fan blade vibration in relation to high-cycle fatigue; and 2) the identification of engine operating points worst for blade vibration. Discussion of these subjects, seemingly little treated in the literature, is presented in terms of an illustrative distillation of hitherto unpublished perspectives in blade stress, dynamics, and their experimental sensing as required for effective design and validation of modern blading. A deliberate effort is made to illustrate design and design verification significance of blade dynamics, and increasingly three-dimensional stress distributions and levels as derived from precision experiments and massive numerical analysis investigations. For example, local time-average stresses three times elementary treatment levels, as generated by the interaction of blade twist, camber, and rim overhang, are indirectly capable of causing fatigue failures, attributable to nonexistent "mystery" vibration. The effectiveness of design verification in extensive simulated flight tests can be enhanced by a systematic identification of operating conditions "worst" for blade vibration. Illustrative examples are given for blade vibration, both stable and self-excited.