Abstract
Tip-rub events, also called blade-casing interactions, are problematic structural phenomena that can lead to complete engine failure. They mainly occur in compressors when a blade tip touches the casing and starts vibrating. If one of the blade natural modes is excited by an engine order, this can lead to an uncontrolled resonance. Therefore, the understanding and the consideration of these interactions is crucial to the development of safe aircraft engines.
Various numerical models and dynamic simulators have been developed, including the in-house one, jm62. It implements a stick-slip model and considers a potential liner and casing wear. Even if it gives precise results, it is computationally expensive and needs a significant amount of post-processing. It is therefore not really adapted to early design stages or quick automated processes (parametric study or optimization).
An automated workflow using SALOME-MECA and its sub-modules had been developed and permits to perform simple and fast parametric studies and shape optimizations. The proposed tool has been used to study the influence of the twist, lean, sweep and tip thickness-to-chord ratio on a modified version of a NASA Rotor 37 blade. The risk of high-level vibration of a blade due to tip-rub events is assessed using the concept of clearance consumption. The clearance consumption is defined as the component of the linear or nonlinear mode shape that defines the distance between the tip of the blade and the casing. From the reference blade and the parametric study results, an optimized candidate was generated using the clearance consumption as the objective function to minimize This process resulted in a geometry with a lower twist angle and a significant forward sweep. Two scenario of tip rub events have been performed on the optimised blades. The testing relies on the in-house time integration software jm62. The candidate has showed a 85% reduction in the amplitude of the vibratory response for the first scenario, demonstrating that the clearance consumption can be used to perform successful shape optimizations for tip-rubbing.
