Dynamic strain prediction and testing of centrifugal compressor blades
This work develops a single stage centrifugal compressor experimental test rig that measures the resonant blade strains caused by unsteady flows in a centrifugal compressor. A time domain coupled fluid-structure computational model is then developed to predict the compressor blade strains on the rotating centrifugal compressor. Although much research has been performed on axial flow turbomachinery, little has been published for radial machines such as centrifugal compressors and radial inflow turbines. This research develops a time domain coupled fluid-structure computational model using commercially available codes. The model couples the codes unidirectionally, where pressures are transferred to the structural code every time step, but the fluid mesh remains unaffected by the structural displacements. A unidirectional coupling is sufficient for this case because blade vibrations are small, the fluid is low density and does not contribute significantly to the mass loading of the blades, and the aerodynamic damping is known. Models are developed for the compressor at blade resonant conditions. The model is then compared with a rotating test of a centrifugal compressor instrumented with blade mounted strain gauges. The test rig is an open loop rig that utilizes an un-shrouded centrifugal compressor with a vaneless diffuser. The strain gauge signals are passed through a high gain, low noise amplifier that is mounted on the rotating compressor. This work not only develops a unidirectionally coupled fluid-structure model capable of predicting dynamic strains, but also provides valuable experimental data that can be used for future research in areas such as blade vibration and aerodynamic damping in radial flow machinery. The data can also be used to validate other fluid-structure interaction (FSI) models.