Vaned Diffuser Induced Impeller Blade Vibrations in a High-Speed Centrifugal Compressor

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades typically originates from unsteady fluid structure interactions. This paper presents the experimental and computational results of a research effort focusing on the blade forced response in a high-speed centrifugal compressor caused by the downstream vaned diffuser. The potential field from the downstream vaned diffuser acts as an unsteady impeller relative circumferentially nonuniform disturbance. In this work the effect of varying the radial gap between impeller exit and diffuser vane leading edges was examined. Dynamic strain gauges, which were installed on the blade surfaces, were used to measure the forced response levels of the blades and to estimate the damping properties for different compressor operating conditions and vaneless gap dimensions. Unsteady fluid flow simulations were used to quantify the forcing function acting on the compressor blades due to impeller-diffuser interaction. The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the diffuser's potential field. The magnitude of the vibratory stress levels was found to depend on the radial gap size, the blade damping properties, and on the compressor operating point. The variation of the radial gap size resulted in a shift of the impeller-diffuser interaction zone towards the main blade leading edge by up to 5% of the streamwise location.