Experimental study of dynamic responses of casing deflection profile for blade rubbing classification

Blade rubbing is one of the most destructive mechanical faults that frequently manifest in rotating machinery. Its occurrence is mainly caused by two distinctively different mechanisms and root causes, namely creep (elongated blades) and rotor eccentricity (diminished blade tip clearance). A successful classification of the types of blade rubbing is important as it could lead to identification of the root cause of the problem. This study explores a vibration method to classify blade rubbing based on the analysis of casing deflection profile. Different types of blade rubbing were simulated in an experimental rotor rig and vibration responses of the rotor casing under the influence of blade rubbing were measured and studied. Experimental results indicate that vibration characteristics of rotor casing change in accordance to different mechanisms of blade rubbing, resulting in fairly distinctive casing deflection profile. A quantitative method to classify blade rubbing was formulated based on the analysis of obtained results. A comparison made against the vibration spectrum analysis suggests that the analysis of casing deflection profile provides a more effective means to classify blade rubbing and therefore could be applied for detailed blade rubbing diagnosis in rotating machinery.