| A key distinguishing feature of multi-blade centrifugal fans is the large width to diameter ratio , b/D2, of their rotor. Another distinctive feature of multi-blade centrifugal fans is that the rotor generally uses a large number of blades of short chord (about 0.1D2). The blades are generally made of a single thickness of sheet metal and are forward curved to assist in obtaining high capacity at low rotational speeds, and thus with low noise. There, large numbers of fans of this type are used in applications requiring low noise, installation size limited, high pressure raised and low cost. This paper focuses on the multi-blade centrifugal fan used in air-conditioning system, where pressure and mass flow rate are high required.Although millions of the multi-blade centrifugal fans are being in use, the initial design method of them is still conventional based on the theory put forward by B.Eck, which mainly composed of experiential formula resulting in great uncertainty when deciding geometrical parameters. This kind of uncertainty of design method makes it difficult and cost-high to develop new multi-blade centrifugal fans with relative better performance because it necessary to do many model experiments to make a choice between different design projects. Fortunately in recent years, thanks to the development of computational hardware and Computational Fluid Dynamics (CFD), CFD techniques have been widely used to simulate the flow patterns and predict the performance of fluid machinery and become a modern industrial design assistant tool. When allied with CFD, the conventional design method of multi-blade centrifugal fans is transformed to modern design method which lessens the model experiments and reduce the cost of new product developing by exploiting CFD which being called as "numerical experiment" also. Based on the conditional design method, this paper developes a soft which mainly consistes two parts, and the first part is multiblade fan design and drawing CAD program with the AutoLISP language which is the main second development tool of the AutoCAD soft; and the other part is the program which automatizates the gridding progress of the multiblade fan model from the CAD program through the JOU format file of Gambit soft. By the soft developed in this paper, the MESH file can be automatically saved in the designated file directory when the required design parameters such as pressure and volume flux rate and etc. having been input. As a result, this paper realizes the integrating the multiblade fan configuration parameter calculating, parameter drawing and model griding.As an example of the CFD numerical simulation applied in the modern design, aimming to increase the outlet pressure or volume flux rate of the multiblade fan , this paper optimize the the geometrical parameters of a multi-blade fan which designed by traditional method including the blade outlet angle, inlet angle and the number of the blade that have great affect on the performance of the fan. By contrasting the pressure, velocity and other specifications distribution of the fans with different geometrical parameters, this paper analyzes how these geometrical parameters influence the performance of the fan. Adopting the optimized parameters, this paper puts forward an optimized fan which has increased outlet pressure and volume rate and more reasonable flow field distribution, recommending a modified experiential formula for deciding the blade number of the fan when designing fan.
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