Influence of Contact on the Structural Response of a Shrouded Fan Blade

Shrouds are often employed on fans and low-pressure turbines to increase natural frequencies and to increase damping. Prevention of flutter and minimization of resonant vibration response is critical to avoiding costly high cycle fatigue problems. Industry experience [Ref. 1] has shown that blade response can be very sensitive to relatively minor variations in design and operating environment. The goal of this study is to estimate the variation in low-frequency vibratory response of a shrouded stage 1 fan rotor due to shroud interface modeling assumptions. In addition to a baseline case that considered no shroud-to-shroud interaction, four shroud interface conditions were considered that covered a range of reasonable possibilities: independent guided edges, standard frictionless contact, standard frictional contact (mu=0.5), standard rough contact (infinite friction). Bonded contact options, while computationally attractive, were not considered since the results can be highly dependent upon the initial shroud geometry. The streamlined modal cyclic symmetry tools introduced in ANSYS 6.1 were utilized, and results from both the prestress and modal analyses were included. The shroud interface assumption was found to have a significant impact on both the frequency and shape of critical modes, and it was observed that the contact assumption that most realistically predicts static behavior might not be the best option for the subsequent modal cyclic symmetry analysis.

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