Excitation of Blade Vibration by Flow Instability in Centrifugal Compressors

Abstract

Experiments were conducted to investigate the interactions between blade vibrations and self-excited flow oscillations in a high performance centrifugal compressor system. Unsteady pressure fluctuations and dynamic stress levels were measured during compressor operation near choke, in self-excited oscillating flow conditions and near surge for four different speed lines. The unsteady pressure field for every operating condition was determined from the simultaneous recording of the output of twelve dynamic pressure transducers which were successively positioned in two peripheral and one meridional planes. Corresponding blade vibration data were collected using an eight channel telemetry system transmitting the outputs of semi-conductor strain gages located on different blades. Analysis of the measurements showed that the unsteady pressure field due to self-excited flow oscillations can be characterized by multiples of rotating and non-rotating pressure patterns at different frequencies. The blade vibration signals clearly demonstrated the excitation of the blade by each of the different unsteady pressure patterns and the frequencies of the unsteady flow field demonstrates the complexity of this flow phenomena and the need to understand the mechanism of its occurrence in order to avoid blade resonance excitation and failure during compressor operation.