Investigation of Blade Vibration of Radial Impellers by Means of Telemetry and Holographic Interferometry

On a high-pressure, high-mass flow, centrifugal compressor blade vibration measurements are carried out to determine the excitation mechanism in various operating ranges. For these experiments semiconductor strain gages were used. For the transmission of the signals, an 8 channel telemetry system has been installed. A research program was started with blade vibration measurements in different operating ranges of the compressor such as rotating stall, surge and flutter ranges and for the case of nonuniform flow conditions. The results of vibration tests with the impeller at rest showed the stress distribution and the strain directions during blade vibration. This information was used for the choice of the strain gage position on the blade. The experimental results were confirmed by a finite-element calculation considering a segment of the impeller with one blade, which determined the different vibration modes. Further, the steady strain distribution of the impeller due to centrifugal force and temperature was calculated. The investigations were completed by optical measurements to find out the vibration modes of the different blades in rotating operation. These tests were carried out by means of a holographic interferometric system with an optical derotator. The results show the various vibration modes of the blade up to a rotational speed of the compressor of 13,000 rpm.