Experiments And Numeircal Simulations Of Noise Reduction Of Axial Flow Fan By Biomimetic Flow Control

With the improving of people’s lives, aerodynamic noise reduction of axial fan has beenput forward higher requirements. Techniques of energy saving and noise reduction based onbionics are widely focused by many researchers. This paper proposes a biomimetic surfacewith rigid ribs and flexible surface inspired by a fish fin surface morphology and materialproperties Experiments and numerical simulations are combined to evaluate the drag and noisereduction performance and flow control mechanism of biomimetic surface on the fan blade.On the pressure surface of a blade, rigid ribs are equally distributed between blade tipand blade root. Rib are arranged in circle and are consistent with the trend of blade tip line.Theorthogonal table ofL49(3)is selected to design the experiment scheme. The factors of thecurrent design of experiment are the rib structure, rib height and the space between the tworibs, and each factor have3levels.3D printing technology is used to print the design of fanmodel and flexible material of EVA is applied in the grooves between the ribs. Under multiplesets of conditions, wind tunnel test and noise test are carried out to compare the performanceof prototypes and bionic axial flow fan.Wind tunnel test results show that the maximum static pressure and the maximum flowrate of the bionic fan blade model are slightly lower than the prototype fan by p Qcurveunder the test voltage. The maximum flow and static pressure are reduced by4%and4.5%under the voltage of7.5V, and are reduced by5.3%and4.6%under the voltage of9.5V.Comparing with the other voltage conditions,7.5V and9.5V voltages show better performancein the maximum flow and static pressure. Through P Qcurve, the bionic axial fan powerconsumption comparing with the prototype fan are reduced by2%~4%under all voltage.Throughη es Qcurve, the maximum static pressure efficiency of No.1and No.2bionicfan increase by10.1%and6.9%under the voltage of7.5V,and maximum static pressureefficiency of No.2,6,8,9bionic fan increase by4.2%,3.4%,3.4%and4.2%under the voltageof7.5V respectively. The noise tests results show that a-weighted sound pressure level of bionic axial fandecline in different degrees and the decrease is more significant in middle and high frequencybands by Spectrum analysis under the voltage of7.5V、8.5V and11.5V. The overall soundpressure level contrast analysis show that most of the bionic axial fans have obvious effect ofnoise reduction. The voltage of7.5V、8.5V and9.5V in the noise reduction performance isbetter than the voltage of5.5V、6.5V、11.5V. Voltage of7.5V and rotational speed of2320RPM, the overall sound pressure level of No.9bionic fan are decreased2.1dB in the thirdmonitoring point. Voltage of8.5V and rotational speed of2580RPM, the overall soundpressure level of No.3、6、9bionic fan are decreased2.1、2.1and2.5dB in the third monitoringpoint. Voltage of11.5V and rotational speed of2980RPM, the overall sound pressure levelare decreased1.6、1.6and1.0dB in the third monitoring point.The numerical analysis of the bionic fan blades of rigid ribs structure on steady-stateanalysis has been studied. The results show that the ribs structure can effectively not onlyimprove the blade surface pressure distribution in the radial direction but also reduce thepressure gradient.This is helpful to inhibit the formation of tip vortex and contribute toimproving the tail gas. By comparison with velocity and total pressure contours of the bionicaxial fans and prototype fan, bionic axial fans can effectively not only control the existence ofthe area of total pressure and velocity concentration of trailing edge but also improve thedistribution of total pressure and velocity in the fan outlet area. This is helpful to reduce theamplitude of pressure fluctuation and then reduce the vortex noise at the trailing edge. Theflexible material can effectively not only absorb and buffer the pressure fluctuations in theboundary layer but also slow the turbulent bursting. This is beneficial to reduce the noise ofturbulent boundary layer. Therefore, the bionic axial fans can effectively reduce the noise ofthe trailing edge shedding vortex, tip vortex and the turbulent boundary layer.