A new approach to optimizing a pump diffuser was presented, based on a three-dimensional inverse design method and a Computational Fluid Dynamics (CFD) technique. The blade shape of the diffuser was designed for a specified distribution of circulation and a given meridional geometry at a low specific speed of 0.109 (non-dimensional) or 280 (m~3/min, m, rpm). To optimize the flow behavior inside the flow passage, the hub and the casing of the diffuser were time and aft-loaded respectively. Numerical calculations using a stage version of Dawes three-dimensional Nervier-Stokes code showed that such a loading distribution can suppress flow separation at the comer region between the hub and the blade suction surface, which was commonly observed with conventional designs of low specific speed diffuser having a compact bowl size (small outer diameter). Substantial improvements in stage efficiency were obtained experimentally compared to a corresponding conventional pump stage, and the application of multi-color oil-film flow visualization technique confirmed that the large area of the comer separation was completely eliminated in the inverse design diffuser.
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