Modal Analysis of Gas Turbine Buckets Using a Digital Test System

A modal analysis was conducted on gas turbine buckets using a digital Fourier analyzer. This digital test/computer system measures a set of frequency response functions for broadband impulse excitation at successive locations on the bucket airfoil. From the set of frequency response functions, the analyzer computes the modal parameters used to determine the natural frequencies, critical damping ratio and mode shapes of the turbine buckets. An animated display of the mode shapes for a discrete experimental model graphically revealed compound modes due to coupling. The test has shown that the digital modal analysis using the impulse excitation technique is a rapid and precise experimental method to determine the modal parameters of turbine buckets with a high degree of repeatability.