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Effect of Steam Turbine Rotor Notch Fillet Radius on Stress and Deformation

A thorough investigation on the effect of a 320MW steam turbine rotor notch fillet radius on thermal and mechanical stresses during start up is presented. The approach consists of a shape design and analysis procedure which incorporates a finite element model. The finite element model is used to characterize the radius of the rotor notch fillet for ensuring the designed thermal and mechanical stress state/pattern and associated deflection during start-up. The results indicate that the notch fillet radius r has significant impact on the total stress of the rotor, in particular on thermal stress. It is determined that the thermal stress is decreased as the notch fillet radius r increases to a critical value. However, the thermal stress becomes saturated as the radius is increased to values larger than the critical value. The results also indicate that the rotor notch fillet radius has little effect on the deflection of the rotor during start-up. This investigation could be very useful to designers for construction of the design guidelines for steam turbine rotors.