| As a primary device in subway ventilation, the reversible axial flow fan is not only used to exchange the gas between the air inside the subway and the one in the outside nature, but used to eliminate smoke and supply fresh air under accidents (such as the fire, the jam, etc.). At present, with the domestic economy fast development, the traffic transportation has gained remarkable achievements. The subway has become an important way to reduce traffic pressure in the city while the surface transportation space is decreasing increasingly, thus the function of the axial flow fan in subway becomes more and more outstanding. Therefore, making researches on the reversible axial flow fan in subway has an important practical significance. The main difference between the reversible axial flow fan and the general one is that the performance of the former is assured not only in the normal ventilation but also in accidents at the same time. The primary factor influencing the performance of the axial flow fan is the aerodynamic performance of the impeller, which is mainly depended on the airfoil of the impeller blade. So how to design the blade of the reversible axial flow fan simply and effectively becomes urgent problem need to be resolved both in theory and in practice. And it is also essential study target of this paper.The CFD software NUMECA is utilized in this paper, and with the aid of numerical experiment method, the flow field inside the reversible axial flow fan in subway is simulated numerically and the blade is designed again for optimization. One type of blade airfoil with high efficiency of a general axial flow fan is adopted as original airfoil, and it is shortened according to different length scale, and then joined to the exportation circular arc of the original airfoil in the opposite direction. Assuring the streamline on the surface of the blade profile after smooth operation, a new kind of double-head anti-unsymmetrical S model airfoils has been structured to be researched in this paper. After analyzing the numerical simulation results of the impeller blade with different scale, and comparing the flow field distributing, then one kind of double-head anti-unsymmetrical S mode airfoils is found which is suitable to the normal and the reversed blowing for double directions under the design operating condition and which can also satisfy the requirement for the reversible axial flow fan in subway.Moreover, it is simulated numerically in this paper for the internal flow in the narrow channel stage within a centrifugal compressor (including the inlet, the impeller, the diffuser, the curved channel and the return channel). One narrow channel stage is adopted as prototype firstly, based on the numerical simulation results, the factors leading to low efficiency in every component are analyzed and found, and then the optimization for the structure of the narrow channel stage is made, which can improve the whole stage efficiency finally. |
