Study On The Effect Of The Aerodynamic Performance Of Open Axial Fan With Concaved Trailing Edge

Because the open axial fan of the open-type axial flow fan covers only a part of the tip of the blade tip near the trailing edge,a very complicated eddy current field exists in the region.At the same time,the internal flow is a kind of extremely complex and unsteady three-dimensional flow.Therefore,scholars have been working hard to optimize and optimize energy-saving noise reduction.Trailing edge modification is one of the methods.This paper is inspired by the evolution of caudal fins that evolved inwards by fishes for efficient swimming,and it is applied to the optimization of the concaved trailing edge of open axial fans.Using bionic methods,different concave structures were designed based on the shape of the caudal fins of the fish.Structural parameters were optimized for the optimal structure.The influence of flow on the external characteristics,pressure field,and tip area of the open-type axial fan were explored,aiming at providing certain guidance and recommendations for the optimization of the trailing edge of an open axial fan.(1)Using bionics method,four kinds of concaved trailing edge structures such as splines,trapezoids,triangles and arcs are designed according to the shape of the fish caudal fins.The aerodynamic performances are compared by numerical simulations and experimental tests.The results show that: at the same rotation speed,the total pressure and power of the scheme with the concaved trailing edge are reduced;with the speed lifting,the acting is the same for the work flow,and the power of each scheme is lower than that of the prototype,so the efficiency is improved,wherein the spline structure is obviously superior to other concaved trailing edge structures,and the energy saving rate in the simulation state is 6.51 %,under the test conditions,the energy saving rate is 14.33%,and the energy saving effect is significant;the blade load reduction distribution of the concaved trailing edge scheme is more uniform,and at the same time,the strength of the tip leakage vortex and the tip vortex is effectively weakened,and the angular separation at the root of the blade is subdued.And the wake intensity at the trailing edge of the leaf is also weakened.(2)The noise experiment shows that under the same work conditions,each concaved structure has little difference with the prototype in the overall sound pressure level,but it can effectively reduce the peak sound pressure level in the low frequency range and improve the uniformity of the sound pressure level distribution,and the low-frequency noise peak Reduce 2 ~ 4dB,effectively improve the sound quality of the fan.(3)The concave depth is changed based on the spline structure.Under the condition of the same work,when the depth of the sag increases,the energy saving rate increases first and then decreases to negative value.Within a certain concave depth range,the load distribution on the blade is improved.The flow efficiency increases,but,when the depth of the concave oversizes,the load distribution on the blade will deteriorate,which reduces its flow efficiency.The optimal depth of the concave is approximately at the position of the chord length of 16%;as the depth of the pit increases,the tip vortex strength and the angular zone separation weaken first and then increase.During the enhancement of the trailing edge concave depth,the tip divergence vortex weakens.The depth of the concave will cause a significant cross-blade depression flow;the fan speed increases with the depth of the concave,resulting in an increase in the angle of attack of the inlet air flow of the blade.As a result,the separation flow at the leading edge is increased.(4)The radial position of the depression is changed on the basis of the spline structure.Under the same rotation speed,the change of the radial position has a greater influence on the total pressure of the fan under small flow,and the total pressure under large flow conditions is basically not affected.The closer the radial position of the concave is to the tip region,the smaller the effect on the total pressure of the fan.When the work is the same,the energy saving rate increases with the radial position of the concave,and the maximum energy saving rate under simulated conditions is 7.50%.With the increase of the radial position of the concave,the high pressure area of the pressure surface of the blade is reduced and the load is reduced,while the low pressure area of the suction surface is reduced mainly at the tip of the blade near the trailing edge,and the tip leakage vortex is weakened.The tip vortex and angular separation have certain inhibition.