Experimental Research On Drag And Noise Reduction Of Blade Of Cooling Fan For Electronic Device With Bionic Flexible Surface

Forced air cooling is the main form of heat dissipation of electronic device. Axialflow fan is the key component in the hot design of electronic device. As power and heatproductivity of electronic devices are increasing greatly. As a result, the power of the fan,the speed and leaf size of fan blade also increase. and consequently the flow loss andaerodynamic noise are more serious. Therefore, reducing flow loss and noise by thebio-insired method has important theoretical value and practical significance.Based on characteristics of fluid biological soft surface with low resistance and lownoise, drag reduction and noise reduction performance of bionic flexible face throughwind tunnel test were explored in this paper. the studies on drag reduction and noisereduction of the blade surface on electronic device cooling fan were also carried outthough experiments. The specific work and results are as follows:The drag reduction of bionic flexible surface on both airfoil NACA4412andNACA6409was studied through wind tunnel test, and the relationship of differentthickness of surface，flow velocity and resistance was obtained. when the speed is lessthan10m/s，five kinds of thickness of bionic flexible surfaces have no drag reductioneffect for airfoil models; when the speed is in the range of10m/s to17m/s，the flexiblesurfaces of thickness of0.2mm、0.4mm、0.6mm and0.8mm can significantly reduce theresistance of the airfoil models and increase its lift. The flexible surface of thickness of0.6mm has the best drag reduction effect among all the bionic flexible surfaces, and therates of drag reduction for the two airfoils are15.79%and11.11%respectively. Theflexible surface of thickness of1mm can not reduce resistance and increase the lift.According to the work conditions of the fan，the scope of linear velocity of the fanblades was fixed. According to the results, the thickness of bionic flexible surface of fanblade was defined to0.6mm. The effects of performance parameters and acousticsperformance of flexible surface on pressure surface，the suction surface，and both on thetwo surface of the blade under conditions of test voltage of10V，12V and14V wereresearched. The test results of the fan indicate that bionic flexible surface can increasethe flow and pressure of fan a little under three kinds of voltage relative to the prototypefan, and the static pressure and total pressure efficiency are improved greatly. Of whichthe fan with bionic flexible surface on the suction surface has the optimal efficiency performance, and the efficiency of static pressure increased by5.21%the efficiency oftotal pressure by5.61%at10V, the efficiency of static pressure by6.27%and theefficiency of total pressure by6.3%at12V, the efficiency of static pressure by6.01%,and the efficiency of total pressure increased by6.2%at14V.The results of noise tests show that：all the flexible surfaces arranged on the fanblades can reduce the noise of cooling fans in low-frequency range, but they can noreduce the noise in the high frequency range. Bionic flexible surface of on the suctionsurface of the fan can reduce the noise with the best effcet, and the fan noise is reducedby1.98dB at10V, by2.05dB at12V, and by2.2dB at14V.Using the basic theory of fluid dynamics and aeroacoustics, mechanism of dragreduction and noise reduction of the flexible surface were also discussed in this paper.First of all, it is recognized that the bionic flexible surfaces has a larger damping relativeto the rigid surface，and they can absorb and buffer the pulsating pressures generated byburst turbulence within the turbulent boundary layer，and then restrain the burstingprocess，which makes the bursting number decline and weakens the acuteness degree.Thereby，friction drag caused by viscosity of the air is decreased. Fouthermore, theflexible surfaces can break off the acoustic feedback mechanism，restrain the generationof vortex， buffer the drop of vortex and intermittent force generated by othermechanisms, which restrain the generation of noise finally.