Acoustic resonance in the inlet scroll of a turbo-compressor

During the commissioning period of a 35 MW turbo-compressor in a natural gas storage station, the vibration level of the compressor rotor increased sharply when the volume flow rate exceeded a critical value. The test results indicated that the acoustic standing waves in the ring chamber formed by the inlet scroll are excited by Vortex shedding from struts in a downstream radial flow chamber. To alleviate vortex shedding from the struts, it was decided to mount small airfoils with a thin trailing edge in the wake of the struts. However, due to design constraints, streamwise gaps and transverse offsets between the struts and the airfoils could not be avoided. To investigate the effect of these gaps and offsets on the resonance mechanism, wind tunnel tests of a simple but conservative model were carried out. Implementing the airfoils into the wakes of the struts suppressed the acoustic resonance mechanism and thereby the rotor vibration at the acoustic resonance frequency was eliminated.