| With the successive introduction of noise environmental protection policies and the increasing quality of life,users have demanded higher requirements for low noise of household appliances related products.Mastering the mechanism of aerodynamic and radiated noise of air conditioner fan system and how to improve the noise level of fan system and application research on the basis of fan design method has become an important research topic.Based on a combination of theoretical analysis,numerical calculation and experimental research,this paper conducts a systematic study on the internal aerodynamic noise and harmonic noise of the air conditioner fan system.It aims to establish the research and control of aerodynamic and radiated noise of air conditioner fan system.The main research contents and innovative results are as follows:1.Based on the systematic summary of the air conditioner fan noise source classification and noise mechanism,it is believed that aerodynamic noise and harmonic noise are the key factors affecting the noise level of the air conditioner fan system;Focus on the flow field and noise control problems in the air conditioner fan system,Carry out research on the noise reduction of outdoor fan blade trailing edge structure and indoor centrifugal fan micro-perforation noise reduction on broadband noise;analyze the influence of the multi-flow operating conditions of the indoor cross-flow fan on the rotating noise;Study the influence of the core structural components of the outdoor unit on the harmonic noise.The purpose of these studies is to achieve accurate positioning of the phenomenon of radiated noise inside the air conditioner fan,by analyzing the flow characteristics and noise generation mechanism,implementing effective noise control methods,and ultimately improving the aeroacoustic performance of the air conditioner fan system.2.The boundary vortex flow(BVF)theory is used to analyze and diagnose the impeller of the outdoor unit,and to explore the relationship between the BVF distribution on the blade surface and the aerodynamic performance of the outdoor unit.The internal flow mechanism and pulsation characteristics of different trailing edge structures of the outdoor unit are studied,and the relationship between the trailing edge structure of the blade and the broadband noise is established.The study found that BVF diagnosis can effectively reflect the internal relationship between the internal flow field and the noise characteristics,and can be used as an important indicator to measure the aerodynamic performance of the outdoor unit fan.The large peak area of BVF appears on the trailing edge of the blade,indicating that the vortex generation rate in these areas has increased sharply,which may increase the flow loss and cause the flow separation phenomenon.The vortex pulsation caused by the trailing edge vortex shedding of the blade is an important cause of broadband noise,and it is very necessary to control the amplitude of the trailing vortex pulsation to reduce the broadband noise.It is found that after the tail edge of the blade is optimized,the amplitude of the low-frequency sound pressure level in the range of94-168 Hz is reduced more significantly.The structure of the trailing edge of the blade has a significant effect on the broadband noise at low frequencies.The fan blade3 solution based on the bionic design concept performs well in reducing broadband noise and low frequency bands,and can effectively reduce the total noise value by 1d B(A).3.Based on the broadband noise characteristics of the indoor centrifugal fans,the silencing principle and design ideas of the micro-perforation silencing are discussed.The application platform for the parametric design of the micro-perforation silencing is built,and the relationship between the micro-perforation parameters and the broadband noise is established.By seting the noise reduction frequency domain for the indoor unit and carrying out the design and experimental research of the micro-perforated muffler,the results of the study found that the total noise value of each windshield was reduced by 1 d B(A)on average,and the noise peak value was reduced by 4 d B(A)on average.The spectrum changes in the frequency domain after the silencing of the micro-perforation are more gentle,without obvious peaks.It is proposed that the micro-perforated muffler can achieve the purpose of reducing noise in the design and calculation frequency domain,which provides a new idea for the application of the micro-perforated muffler in the field of home appliances in the future.4.The internal flow pattern and the aerodynamic characteristics of the rotating noise in the transient process of the indoor cross flow fan under different flow conditions are studied,and the relationship between the internal flow characteristics and the noise characteristics of the multi-conditions is established.The results show that as the flow rate decreases,the area of the eccentric vortex increases,and along with the decrease in the area of the duct flow area,the airflow diffusion at the outlet is strengthened,and the airflow uniformity becomes worse and worse.The study found that the trailing edge of the blade appeared near the exit position of the volute tongue structure,and the eccentric vortex flow field was formed by these shedding vortices finally converging together.There is an obvious wake near the volute tongue and the trailing edge of the blade,which interferes with the motion and static of the blade to produce pressure pulsation,which ultimately leads to the generation of rotating noise.The test noise spectrum shows:when the indoor unit is under 1.33Q_d flow conditions,its blade passing frequency and harmonic frequency,the spectrum shows a significant noise peak.This shows that the rotating noise caused by dynamic and static interference is the main cause of aerodynamic noise.When the fan is working under0.4Q_d conditions,the maximum noise peak appears at a frequency of 50 Hz,and the second peak appears at 0.86 times the blade passing frequency,and the noise peak is not obvious at the blade passing frequency.This indicates that the unstable flow caused by the eccentric vortex flow is the main cause of aerodynamic noise under this flow condition.5.The harmonic theory of outdoor unit and the mechanism of harmonic noise generation are studied,a vibration test platform is built,and the influence of the core structural components of the outdoor unit on the harmonic noise is analyzed.The study found that the structure of the motor and the motor bracket has an impact on the anti-harmonic ability and noise quality of the outdoor unit.It is proposed that the anti-harmonic ability can be improved by optimizing the modal frequency of the bracket to avoided the motor excitation frequency.The results show that the noise peak at 186 Hz is reduced by 4 d B(A),and the noise peak at 214 Hz is reduced by 8d B(A).After optimization,the anti-harmonic ability of the motor bracket is improved.The outdoor unit produces a noise peak at a frequency of 200 Hz under the harmonic power supply,and its noise peak gradually increases with the increase of the harmonic content.It is proposed that the plastic package motor has a good ability to reduce the harmonic noise,and the noise peak at the rotating frequency of the motor can be used to reduce the harmonic noise of the outdoor unit by using the plastic package motor. |
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