| Small axial fan is the main heat sink of electronic products,whose performance determines the operation status and service life of the electronic products directly.With the development of electronic products toward integration and high power,the requirements of heat dissipation are increasing.Besides,more and more people pay attention to the ventilation performance and noise performance of small axial fan.Therefore,it is very necessary to optimize the structure of small axial fan and to carry out the analysis of its static characteristics,aerodynamic noise and internal flow characteristics.In this paper,single rotor small axial fan with five blades is regarded as the prototype,the unequally spaced fans with different maximum angular displacements and the fans with inlet guide vanes with different outlet angles of inlet guide vanes are designed respectively through the improved blade structures of single rotor.Based on the calculation of the flow field,the unequally spaced fan and the fan with inlet guide vanes with the best effects of noise reduction are selected under the condition that the static characteristics can meet the requirements,which are labeled as model 1 and model 2,respectively.Static characteristics,aerodynamic noise and internal flow characteristics of the prototype and the model 1,the prototype and the model 2 are compared and analyzed.The experiments of static characteristics and noise of the prototype,the model 1 and the model 2 are carried out.The main contents and results of this paper are as follows:(1)The single rotor small axial fan with five blades is regarded as the prototype.Thirteen kinds of unequally spaced fans with different maximum angular displacements are designed according to the blade angular modulation method.Four kinds of fans with inlet guide vanes with different outlet angles of inlet guide vanes are designed according to the design requirements of the inlet guide vanes.Numerical simulation methods adopted in this paper are introduced.(2)The results of numerical simulation show that the unequally spaced fan with maximum angular displacement of 6 degrees and the fan with inlet guide vanes with outlet angle of 60 degrees have the best effect of noise reduction under the condition that the static characteristics can meet the requirements at rated conditions,which are labeled as model 1 and model 2,respectively.Compared to the prototype,the static characteristics of the model 1 remainunchanged basically,while the static characteristics of the model 2 are improved significantly.(3)The research results of flow field show that the noise in the near field is dominated by discrete noise,mainly caused by the total pressure fluctuation.The model 1 and the model 2 can reduce the discrete noise in the near field of the prototype.The noise in the far field is dominated by broadband noise,which mainly related to the factors including the distribution of vorticity,the variation of vorticity etc.This two kinds of blade structures of single rotor have a little effect on the broadband noise in the far field of the prototype.(4)The static characteristic experiments of the prototype,the model 1 and the model 2 are completed in the wind tunnel test bench.Experimental results show that the numerical simulation is reliable.The unequally spaced blades with maximum angular displacement of 6degrees do not change the static characteristics of the prototype significantly,while the static pressure of the prototype at rated condition increased by 1.8 Pa after installing the inlet guide vanes with outlet angle of 60 degrees.(5)The noise test of the prototype,the model 1 and the model 2 is carried out in a semi-anechoic room.The experimental results show that compared to the prototype,the maximal noise reduction of the model 1 and the model 2 in the downstream of the fan along the axial direction are both located at the test point where is 100 mm away from the fan and the noise decreases by 1.5 dB and 1.2 dB,respectively.For the test points whose distance away from the fan is larger than or equal to 400 mm,the noise of the optimization model is consistent with the prototype.In summary,the single rotor small axial fan with reasonable distribution of unequally spaced blades can reduce the discrete noise in the near field under the condition that the static characteristics remain unchanged basically,while installing the inlet guide vanes with reasonable outlet angle can not only significantly promote the static characteristics of single rotor small axial fan,but also reduce the discrete noise in the near field and improve the internal flow characteristics.This paper will provide the basis for the optimization of the single rotor blade structures of small axial fan with high static characteristics and low noise. |
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