Severe rubs between gas turbine blades and engine casings can in extreme cases result in damaging blade vibration levels and rapid loss of casing lining material. Even for more minor rubs, the wear in the lining material will result in increase tip gaps and a consequent loss in efficiency. Major rub events are extremely rare in practice, and there is seldom any useful diagnostic evidence of the root cause of the behaviour. Moreover, traditional analysis methods are not suitable for exploring the wide range of potential conditions under which an unstable vibration response might be initiated. A new modelling technique has been developed for modelling blade casing rubs which includes a detailed model of the interaction with liner wear. The method is time based, but is very efficient, enabling a wide range of initiating conditions to be explored. A series of examples have been developed to firstly: demonstrate the method is robust and reliable, and secondly: to investigate potential interaction phenomena under representative simulated conditions. The method has been applied to a real blade example, for which severe wear is known to have occurred. The method predicts that instability may occur above a threshold level of tip rub severity, and also demonstrates the improvement in an alternative blade design for which rub tolerance is known to be superior.

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