Fractural Damage Analysis and Optimized Improvement for Last Stage Moving Blade in ECST

Based on the static strength calculation, the fracture reason was examined for the last stage moving blades of an Extraction Condensing Steam Turbine (ECST) in a power plant. The calculations revealed that the original blade design was unreasonable, which resulted in the compound stress exceeding the material allowable stress. The study was focused on redesigning the broken moving blade by means of three-dimensional design on the premise of satisfying the static strength requirement. Furthermore, by using commercial CFD (Computational Fluid Dynamics) software NUMECA, the flow field was simulated and analyzed for both the last stage and the penultimate stage under the circumstances of unbroken and broken, so was it for the redesigned last stage. Detailed discussion was given to the influence of the broken blades on the performance of the whole stage, and feasible conclusions were drawn on the improved moving blades. It was shown that the redesigned moving blades produced a good performance under practical operation.