We developed a technique for designing forward curved bladed fans using computational fluid dynamics (CFD) and numerical optimization. The target is a forward curved bladed fan including an impeller with blades and a volute casing. In our research, we developed a two-step calculation method with a blade-to-blade grid model and a full grid model. Using these models individually according to purpose, we reduced the design time by one quarter. An automatic grid-generation program that was developed in-house generated the grids for the CFD calculation. The fan performance was calculated using commercial CFD software based on an incompressible Reynolds-averaged Navier-Stokes (RANS) solver. For numerical optimization, we used a simulated annealing algorithm (SA) to determine the optimized design variables. Using the developed technique, we attempted to minimize the total pressure loss of an impeller and a suction cone. We could obtain the optimized design variables: the gap between the impeller and suction cone, the inside diameter of the shroud rim cover and the number of blades. Our results demonstrated that the optimized fan design had smaller shaft power than the initial design, especially at the low flow rate. Clearly therefore, our technique is capable of designing an energy saving fan in a short time. Moreover, it was found that that the leak flow between the impeller and suction cone of the optimized fan was suppressed. The change in these design variables contributed to this suppression.

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