Numerical Simulation Of Aerodynamic Noise And Noise Reduction Scheme Of Air Duct T-elbow Of Ventilation And Air Conditioning

The“China's environmental noise pollution prevention and control report?2018?”^[1]pointed out that environmental noise complaints accounted for 56.4%of the total environmental complaints.Among the environmental noise,the total construction noise complaints accounted for as high as 46.1%,and 28.6%of the building environmental complaints were caused by air-conditioning systems.With the improvement of people's requirements on the living environment,the issue of air conditioning noise control urgently needs to be resolved.The noise of the air-conditioning system includes the noise of the unit and the ventilation system.With the development and application of new technologies,the noise of the equipment of the ventilation and air conditioning system such as compressors and cooling towers has been greatly reduced.Aerodynamic noise has gradually become the main noise source of HVAC systems in indoor living areas.From the perspective of acoustic noise reduction,the study on the influence of the structural form of the local components and the flow field in the pipe on the noise source has important guiding significance for the HVAC system design and environmental noise control in practical engineering.The aerodynamic noise of the pipeline system is mainly concentrated in the structural mutation of the pipeline.The local components of the air-conditioning ventilation duct system include diameter reduction,valves,elbows,T-elbows,four-legged etc.In this study,the local components represented by the shunt T-elbow are taken as the research object,and the pipeline acoustic analysis and noise reduction measures are studied.Through theoretical analysis and numerical simulation,the mechanism of airflow regeneration noise due to the existence of local components in the air conditioning and ventilation system is revealed.The reliability of the numerical simulation results is verified by comparing with the test results of similar experiments in the literature.Then through numerical simulation to analyze the actual structure in the project,the main inlet flow velocity V₁,the ratio of the flow rate of the branch pipe to the main pipe Q₃/Q₁ and the ratio of the pipe cross section to the aerodynamic noise,and obtain the influence law of different action factors on the sound field.The results show that the aerodynamic noise inside the shunt T-elbow mainly comes from the dipole sound source formed by the pressure pulsation on the wall of the pipe,which is mostly affected by the inlet velocity V₁,followed by the influence of the structural transition form before the inlet of the branch pipe and the flow ratio Q₃/Q₁.Through the analysis on the sound source intensity and the sound pressure level spectrum of the monitoring points in the sound field under the conditions of different inflow velocities?5.5.m/s?10m/s?and the flow ratio of the downstream of the branch pipe?20%?38%?,the noise reduction design scheme of the aerodynamic noise in the shunt T-elbow is obtained.To verify the actual effect of the noise reduction design scheme,by comparing the sound pressure level of each frequency of the sound field monitoring point with the NR limit of the noise evaluation curve,the working conditions that meet the NR curve are summarized,and the reasonable acoustic design in engineering is illustrated.The practical significance of the structure is finally obtained in line with the airflow noise control of the pipeline.