A new technique for identifying synchronous resonances using tip-timing

Non-contact measurement of vibration at turbomachinery rotor blade rips usi ng blade rip-timing has become an industry-standard procedure. Current rese arch focuses on analysis methods for interpretation of the measured vibrati on data from a limited number of probes. The methods are classified by the form of the vibration they can identify. identification of asynchronous res ponse amplitude and frequency is well documented. Whilst a method for ident ifying maximum synchronous resonance amplitude has existed since the early. 1970s, there is no published evidence of a method for directly identifying frequency or engine order using a small number of probes. This paper prese nts a new analysis method for identifying synchronous resonance engine orde r using two tip-timing vibration measurements. The measurements are made at different locations on the turbo-machinery casing using a minimum of two p robes. A detailed description of the method and results from its practical application are given. The potential of the method to identify the amplitud e and frequency of close modes. not possible with current methods. is demon strated. The effect of blade mistuning on the accuracy of the method is inv estigated. Existing synchronous response analysis methods and the new metho d presented here give the response amplitude and frequency after the resona nce has been traversed. Real-time identification of synchronous response am plitude and frequency would allow tip-timing to be used as a safety monitor of all blades. Real-time methods, their limitations and practical applicat ion are discussed. The future use of tip-timing as the dominant vibration m easurement system is discussed with reference to experience on measurements made solely with tip-timing on assemblies with undefined vibration charact eristics.