Numerical Investigation Of Blade Tip And Guide Vane Structure On Performance And Aerodynamic Noise Of Axial Flow Fans

In the impeller machinery,blades play a vital role position,and the operating conditions of impellers and guide vanes have a significant impact on the overall performance and safety.In this study,a two-stage variable-pitch axial fan is selected and Solid Works is used for modeling.Five schemes including single counterflow rib layout grooved tip are numerically simulated to analyze its internal flow characteristics,pressure distribution,and loss characteristics,and finally,the optimal scheme is determined.In addition,four schemes of first-stage guide vanes are studied,the internal flow characteristics and static structure changes of the fan before and after modification are examined,and the influence on the performance of the fan is explored.For a two-stage variable-pitch axial fan,different grooves combined with winglet tip structures were constructed.The results showed that compared with the original structure,the total pressure rise and efficiency of four different schemes have been improved to different degrees,and the scheme 4 of the groove top with double counter-flow ribs presents the best performance.After the tip modification,the flow field at the tip clearance is more complicated.The vorticity in the tip clearance has been greatly raised under the four schemes,and the maximum vorticity is increased by about 10000-30000 s^-1.Compared with the original structure,the tip leakage flow under the four schemes has been reduced to some extent,as follows:Scheme 1,Scheme 2,Scheme 4,and Scheme 3.The steady results are used as the initial field for strength check,modal analysis,and noise estimation.The maximum deformation of four schemes is lower than that of the original structure;the natural frequencies of each order before and after modification avoid the passing frequency;when the winglet-groove tip combination is used,the noise spectrum of the fan changes to a certain extent.Although the double-ribbed groove tip structure has the best aerodynamic performance,the noise increase is relatively apparent.In practical applications,appropriate noise reduction measures need to be taken.The guide vane structure of another two-stage variable-pitch axial fan was studied,and three different first-stage guide vane structures were suggested.Case 1 was to change all the short guide vanes into long guide vanes;case 2 was hollow guide vanes,case 3 is that all blades are long blades,and the effect on the fan performance is explored.The results show that:for the total pressure of the fan,compared with the original structure,the total pressure of the modified guide vane is slightly reduced,case 2 has a small increase under small flow,and case 3 has a significant increase in the full flow range with the average increase of about 5.2%.Regarding the efficiency of the fan,case1 is less effective,case 2 and case 3 have a significant improvement in the full flow range,and case 3 present a better improvement with an average increase of 3.5%.When using equal-length long blades,the flow field of the first-stage guide vane and the second-stage moving blades is improved,and the mixing of adjacent fluids is reduced at the trailing edge of the blade,the pressure and velocity distribution is more uniform,and the tailing flow distribution is better.The static structure results show that the change of the guide vane structure basically has no effect on the stress and deformation of the two-stage rotor;case 3 changing all guide vanes to long blades n meets the specified requirements,the strength and rigidity of the blades are slightly improved.