Research On Flow Field And Aerodynamic Noise Of Axial Fan Of Window Air Conditioner

Window air conditioners have great market in the Middle East?the Europe and the United States,because of manufacturing materials less,low cost,simple installation,small size,convenient disassembly.The refrigeration systems of window air conditioner are concentrated in a chassis,so its noise is large.Axial flow fan is the main ventilation heat-dissipating component in the outdoor part of window air conditioner and its ventilation volume will directly affect whether the window air conditioner can work normally.Noise will affect people~'s normal work and rest.It has become a key issue for improving the market competitiveness of window air conditioner to design axial flow fans having low-noise.It has important guiding significance for improving the aerodynamic performance of the axial flow fan and designing axial flow fan with low noise to study deeply the internal flow field and noise mechanism of the axial flow fan.Semi-open axial flow fan with water ring used in outdoor unit of window air conditioner was researched in this article.Its blade diameter,hub ration,height of hub,height of axial fan were 300mm,0.2,40mm and 77mm respectively.It has 4 blades.Water loop surrounds the outer peripheral of blade tip and connected to the tip of each blade.There are 4 bumps distributing evenly along the inner side of the water loop.The effect of different concave shapes and sizes of blade trailing edge on the aeroacoustic performance of axial flow fan were studied.Firstly,a three-dimensional steady-state numerical simulation has been designed to study the internal flow field of axial flow fan with water ring in outdoor unit of window air conditioner based on multi-component coupling by Navier-Stokes equations coupled with standard k-?turbulence model.The CFD calculation model which can predict aerodynamic noise was established.The methods for treating the heat exchanger as porous media,air flux at different speeds and the generation,development and dissipation of tip vortex was analyzed.The result show that flow at outlet increases linearly with speed of axial flow fan.Heat exchanger has a great influence on flow.Tip vortex forms on the blade suction surface near the leading edge,moving in the circumferential direction opposite the direction of rotation of the impeller,disappearing at the tip of suction surface near the trailing edge.The pressure of blade tip and trailing edge areas is maximum and they are the main noise source area.It provides the basis for improving the structure of the axial flow fan.Secondly,the unsteady numerical simulation was designed to analysis axial flow fan before and after optimization by LES and Fluent.FW-H sonic wave equation based on Lighthill sound analogy was applied in predicting far-field aerodynamic noise of the axial flow fans.The relationship between speed and sound pressure level,sound pressure level directional distribution were analyzed.The effect of blade trailing edge depression on sound pressure level,noise spectrum and 1/3 octave sound pressure spectrum of axial flow fan was discussed.Influence of different dimensions of arc-shaped sawtooth trailing edge structure on sound pressure level of axial flow fan was analyzed and discussed.Research indicates trailing edge depressions can reduce aerodynamic noise of axial flow fan.It mainly affects broadband noise and has a little effect on discrete noise.To axial flow fan with trailing edge of circular serration,the aerodynamic noise firstly decreases and then tends to remain stable with increasing of sawtooth size.The closer the sawtooth size is to the width of the trail,the better the noise reduces.Finally,in order to verify the accuracy of the simulation,an experimental research has been designed to study the aerodynamic noise of axial flow fans.The sound pressure level at exit of axial flow fan was measured by high-precision sound pressure sensor in semi-anechoic chamber.Noise-speed characteristics and sound pressure directivity distribution of original fan and concaved trailing edge fan were researched.Sound pressure spectrogram and 1/3octave sound pressure spectrum of the two impellers were analyzed.The results of the experiment show that sound pressure levels of axial flow fan are not the same in different directions and it presents Irregular curve distribution.Sound pressure level in the direction of the air outlet is largest.Aerodynamic noise propagates mainly in the direction of the axis of rotation of the fan.The trailing edge local depression can reduce aerodynamic noise of axial flow fan.It can reduce 3dB(A)to 5dB(A)at the downstream of axial direction and 1m away from the axial flow fan.The experimental results are consistent with the simulation results.