Development of whole-machine high speed balance approach for turbomachinery shaft system with N + 1 supports

It is very challenging to conduct dynamic balance for turbomachinery shaft system with N + 1 supports due to complex bending deformation, less measurement information, and unavoidable testing condition constrains. However, dynamic balance is needed to reduce the number of rotor startups and ensure the operation safety. The influence coefficient balance method has been used for the shaft system by moving required balancing rotor disks. In this paper, a whole-machine dynamic balance method is proposed. The proposed approach is developed based on the multi-plane influence coefficients balance method without applying trial masses. It only needs the initial responses of synchronous vibration and a finite element model (FEM). The multi-plane influence coefficients under different speeds are calculated based on the steady state response predictions from the FEM instead of using measured responses as used in other traditional balance approaches. Thus, the correction masses along the shaft are determined numerically to balance the shaft system with high efficiency. The proposed dynamic balance method was validated experimentally using a shaft system with four rotors and five bearings which rotating up to 2700 rpm. The dynamic balance was clearly demonstrated. Average reduction of bearing vibration amplitude is 25%. Maximum 53% reduction is observed under 2700 rpm which is above the fourth critical speed of the shaft system.