Influence Of Bionic Structure On Aerodynamic And Acoustic Performance Of Axial Flow Fans

The variable pitch axial flow fan is widely used in the actual production of power plants due to its high economy,reliable structure and wide range of use.However,as the pressure ratio and the rotational speed of the axial flow fan continue to increase,the resulting noise pollution and safety problems are becoming more and more important.The aerodynamic noise generated by the long-term work of the fan blades seriously jeopardizes the physical and mental health of the power station staff;the instability of the internal flow of the fan will cause periodic pressure pulsation of the fan,and severely cause a stall and flow deterioration.Therefore,it is of great practical significance to study the flow characteristics of axial flow fans and to modify the structure of the fans to have better aerodynamic characteristics,which can reduce the noise pollution of the fans and improve the working stability of the fans.The concept of biology provides new ideas for solving many industrial problems.Owls have the characteristics of quietness and stability when diving.This article imitates the unique biological structure of owl,and installs the serrated trailing edge on the axial fan blade.Based on the CFD numerical calculation software,the numerical simulation method is used to carry out the analysis.The research shows that the bionic trailing edge of bionics can effectively reduce the noise of the fan,and the noise reduction effects of diverse sizes of serrations are different.The influence of the serrated length on noise reduction is more significant.The serrated trailing edge can suppress the noise "hump" in the middle frequency band,so the noise reduction effect in the low-frequency band is better.The bionic serrated trailing edge improves the fan efficiency of the variable pitch axial fan at the low flow rate and standard operating conditions,and the efficient area of the fan operation to the small flow rate.At the large flow rate,the serrated trailing edge reduces the efficiency of the fan.The longer the serration is,the more obvious it is.but it can be compensated by changing the mounting angle of the blade in advance.However,the advantages of the variable pitch axial flow fan can be used to compensate for it by changing the mounting angle of the blade in advance.The serrated trailing edge reduces the pressure pulsation amplitude of the fan channel and increases fan stability.The greater the length of the serration,the better the stability.After using the serrated trailing edge,a uniform "tubular" vortex can be generated,which improves the distribution of the vortex and reduces the size of the shedding vortex.A double-layer "comb" vortex structure was discovered and the mechanism analysis was given.The bionics serrated trailing edge was further optimized,and a long serrated trailing edge was set only in the middle of the blade trailing edge,and the remaining position remained the same.This method retains the high-efficiency noise reduction capability of the long serrated trailing edge,and at the same time compensates for the defects of the performance of the fan at the large flow rate when using long serration.The serrations are cut at the trailing edge of the guide vane,and the long serration can effectively improve the fan efficiency on the large flow side,and the noise reduction capability is more obvious.The flat serrated teeth are obtained on the basis of the conventional serration,and the full pressure and efficiency of the serrated trailing edge modified fan can be improved at the full flow rate.Flat-tip serrations can reduce the aerodynamic noise in the flow path of the original fan,especially at the bottom of the flow channel,but because the flat-pointed serrations cannot suppress the "hump" phenomenon in the noise distribution,the noise reduction effect in the high part of the flow channel is not as good as the conventional serration.Obtaining flat serrations on the basis of conventional serrations can improve the full pressure and efficiency of the serrated trailing edge modified fan at full flow,increase the full pressure by 66 Pa near the design condition point,and increase the efficiency by 1.4%.But the noise reduction effect is not as good as conventional serrations.