The Unsteady Flow and Forced Response for a Variable Nozzle Turbine

摘要

Variable nozzle turbine (VNT) has become a popular technology for diesel application. While one of the major challenges for VNT is resonant vibration due to the fluctuating pressure in unsteady flow. Both the leakage flow forms inside the nozzle clearances and the shock produces under small nozzle openings increase the flow unsteadiness inside downstream rotor tunnel. In this paper, the unsteady simulation of the turbine was conducted to investigate the effects of nozzle clearances and openings on the transient load fluctuation of the blades. Then a finite element model of turbine wheel was built and blade forced response was simulated with harmonic analysis. The results showed that the decrease of nozzle opening would intensify rotor vibration and increase the blade dynamic stress. The simulation of blade resonance showed that the 1st order resonance located at the blade trailing edge while the 2nd order resonance happened at the leading edge, which was consistent with the blade actual crack.