Modeling of microslip friction and design of frictionally constrained turbine blade systems

Turbine engine designers frequently employ dry friction damping devices to reduce blade vibration. Traditionally, these damping devices are designed through the use of experience and lab testing until macroslip friction models have been developed to estimate friction force since the early 1980s. Macroslip friction models, however, could be inaccurate in predicting the friction force under some situations, e.g., in case of high contact pressure.; To advance friction modeling technique, this research aims to establish accurate yet practical microslip friction models so as to evaluate the induced friction force and then lump the friction force into two distinct terms, stiffness and damping, which are subsequently incorporated into the harmonic balance method to predict resonant response of frictionally constrained blades. Four types of contact kinematics are investigated: (1) non-uniform normal load distribution, (2) normal load variation, (3) 2D slip motion, and (4) coupling between normal load variation and 2D slip motion. The investigation leads to the development of the following friction models: (1) 1D slip motion microslip friction model having time invariant normal load, (2) 1D slip motion microslip friction model having time variant normal load, and (3) 2D slip motion having time variant normal load. The application of these friction models to the prediction of resonant response of frictionally constrained turbine blades is also presented.; In turbine blade systems, the blade tip could intermittently rub the casing, leading to the system instability under certain conditions. An interface model with one of its contacting bodies driven by an external source is developed to model the friction force between the blade tip and the casing. It has been numerically shown that a limit cycle could exist in the case of system instability. A limit cycle prediction method is developed.; In the design of practical turbine blade systems, the objective of lowering the vibration experienced by turbine blade systems during engine operation is even deteriorated by the existence of rogue blades—lone blades, instead of the entire structure, that exhibit unexpected fatigue failure. In this research, the combined effects of shroud contact damping and structural mistuning on the forced response of mistuned turbine blade system are examined.