Transient vibration characteristics of a rotating multi-packet blade system excited by multiple nozzle forces

•A dynamic model of rotating multi-packet blade system subject to multiple nozzle forces is proposed.•Resonance frequencies and their strengths are investigated with the dynamic model.•Effects of system parameters on the steady state and transient responses are investigated.

For the design of a rotating multi-packet blade system excited by multiple nozzle forces, transient and steady-state vibration characteristics of the system need to be identified accurately. The present study derives equations of motion of a rotating multi-packet blade system excited by multiple nozzle forces using the Rayleigh–Ritz assumed mode method. Using the equation model, resonance frequencies and their strengths are first identified. The study then investigates the effects of system parameters such as number of nozzles, number of packets, shroud coupling stiffness, disk coupling stiffness, damping constant and spin-up time constant on the transient response during a spin-up or spin-down motion which makes the nozzle passing excitation frequency pass through multiple resonance frequencies as well as the steady-state response around an operating angular speed.