Optimizing Instrumentation When Measuring Jet Engine Blade Vibration

Abstract

An analytical model of bladed disk vibration is used to calculate the statistical variations in blade amplitudes that can occur in mistuned turbomachinery blading. The results provide a basis for evaluating alternative strategies for instrumenting the stage. This approach is illustrated by applying it to an unshrouded fan stage. It is found for this stage that the best strategy is to instrument blades that have frequencies near the tuned system frequency. A procedure is proposed for establishing how gages should be allocated from stage to stage throughout the engine.