Blade Vibration Measurements on Centrifugal Compressors by Means of Telemetry and Holographic Interferometry

Blade vibration measurements have been carried out on a high-pressure, high mass-flow centrifugal compressor to determine the excitation mechanism. For the experimental investigation, semiconductor strain gages with a multichannel telemetry system were used. The measuring points on the blades have been chosen using the results of a stress calculation for the vibrating blade by means of the FE-method. A research program was started with blade vibration measurements in different operating ranges of the compressor and with two types of diffusers. Results are presented for the blade excitations obtained by throttling the compressor at various rotational speeds and for the cases of passing resonances by increasing the rotational speed at constant throttle valve position. Results were obtained for blade excitations caused by: 1) the nonuniformity of the flow in the diffuser, 2) the stalled flow near the surge-line, 3) the blades of a vaned diffuser and 4) the surge. The investigations have been completed by optical measurements to find out the vibrational modes of the different blades in rotating operation. These tests were carried out by means of a holographic interferometric system using an optical derotator up to a rotational speed of n = 20,500 rpm.