Research On Aerodynamic Noise Characteristics And Noise Reduction Mechanism Of Large Marine Axial Fan

Large marine axial flow fan(AFF) as a key equipment of ship cabin for ventilation and air exchange, is widely used in large ship cabin, sending air to cabin. Aerodynamic noise as the main noise source of AFF, become one of the important indexes of evaluating the fan's performance. Therefore, it is necessary to reduce the aerodynamic noise of AFF effectively.In this paper, by numerical limulation and experimental test with the large marine axial flow fan(AFF), the blade perforation's influences on its internal flow field and aerodynamic noise characteristics are analyzed deeply. And a kind of new type axial flow fan with perforated blades is designed. Meanwhile, the main noise reduction mechanism of the AFF with peforated blades were analyzed to provide the reference for reducing the noise of the large marine AFF. Research work and achievement of this paper are as follows:1.UG NX7.0 is selected as the 3D modeling software for modeling in this paper, and the commonly used function module and product design process of this software are introduced. By which, the impeller of the large marine AFF is modeled.2. The simulation model of the internal flow field in the large marine AFF was established by the CFD software. Under the rotate speed of 1460 rpm, the flow characteristics in the axial flow fan at different working conditions were analyzed, such as the outlet pressure and efficiency along with the change of flow rate, and the distribution of pressure and velocity, the formation process and mutual relations of the air flow in the impeller region. The analysis shows that, in the region of the blade tip, the tip clearance noise caused by the tip clearance vortex is the main aerodynamic noise of the axial flow fan;and the trend of distribution of turbulence intensity and sound power level is relatively consistent, so the turbulence intensity is the dominant influence factor of the noise distribution.3. On the basis of the steady state calculation, the perforation design is conducted for the large marine AFF. With the unsteady calculation model established, the optimal perforation parameters are determined by numerical simulation. While analyzing the effect of perforation parameters on the noise reduction AFF, it can be found that the total noise level distribution fluctuates with the increase of the hole diameter, and when the perforation diameter D is fixed, the total noise lever reduces along with increasing in the perforation deflection angle ?, which present to be a linear variation. It can be explained reasonably by acoustic interference phenomenon. Meanwhile, the performance and noise of the fan istested by the large marine axial flow fan performance test bench and noise test system.Through analysis, the simulation results was verified.4. Through the analysis of the internal flow characteristics and the noise spectrum at the monitoring point, the noise reduction mechanism of the large marine AFF with perforated blades is studied. Through the analysis of the streamline distribution inside the fan flow, the surface static pressure distribution on blade surface, the vorticity distribution of internal flow field, the noise distribution in the flow passage, and the noise spectrum at the tip clearance, it can be found that, after perforation, the flow of the internal field is improved,the flow separation and backflow were suppressed, and the vortex shedding at blade trailing edge is suppressed to reduce the noise.