662 / 2019-04-26 14:46:31

Aerodynamic Damping Calculation of Steam Turbine Last Stage Moving Blades Based on Harmonic Balance Method

Harmonic Balance method,Last stage moving blades,Aerodynamic damping,Flutter,Inter-blade phase angle

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The increasing demand for power generation makes the exhaust area of LP cylinders continuously expand, which forces the last stage moving blades (LSMBs) become longer and thinner. This kind of long blade is very sensitive to flutter (aeroelastic instability) due to its aerodynamic and structural natures. Although the long blades of modern steam turbine are often damped by dampers such as part-span connector and blade shroud, researches on the aeroelastic stability of the blades, as part of the early design of the blades, are unavoidable. In present work, a loosely coupled simulation of LP steam turbine LSMBs under designed condition is studied using Harmonic Balance Method. The influence of vibration mode on aerodynamic damping is analyzed and flutter characteristics in first mode family of one blade both in unshrouded and shrouded forms are calculated in different inter-blade phase angles (IBPAs). The results show that for unshrouded blade, there is a period range (about -30° to -150°) in flutter situation but the shrouded blade is always damped. Time-averaged wall power density for both forms are also presented in IBPA ±90°.