| Ventilation and air conditioning systems are essential for creating a healthy and comfortable indoor environment.With the continuous improvement of the sound environment quality of buildings,people’s tolerance for noise is gradually reduced,and the noise of ventilation and air-conditioning systems has become one of the urgent problems to be solved.Ventilation and air conditioning system noise is not a single sound source,but is composed of equipment noise generated by ventilation and air-conditioning equipment and air flow regeneration noise generated by air duct systems.Currently,the research on equipment noise is relatively mature.Airflow noise of duct system includes the fan noise and the pipeline air flow regeneration noise,which are mainly concentrated in the air duct,various local components,and the parts where the velocity changes suddenly.In practical engineering applications,some ventilation and air conditioning systems have the defects of unreasonable acoustic structure in the design,and the pressure pulsation generated by the sudden change of the flow velocity of the fluid in the pipeline produces aerodynamic noise.When the aerodynamic noise at a local point in the pipeline is higher than the noise transmitted by the fan,it will become the dominant noise of the system,causing the indoor noise value to exceed the standard and polluting the indoor acoustic environment of the building.Therefore,researching and reducing the airflow noise of the air duct has become the key to controlling the noise of the ventilation and air conditioning system.At present,the research on ventilation and air conditioning duct system is usually from the perspective of reducing resistance and consumption,but the research on the noise reduction of duct air flow is less.Airflow noise calculation is mostly based on empirical or semi-empirical formulas.And the experimental studies in the literature are mostly single-point comparative measurements,and the noise reduction is lacking effective theoretical guidance.In this paper,the problem of pipe airflow regeneration noise caused by the partial components represented by the confluent T-elbow is the starting point,and the numerical simulation of aerodynamic noise in the tee is carried out by the method of co-simulation of computational fluid dynamics(CFD)and acoustic finite element software(LMS Virtual.Lab).Based on the sound pressure of fluid and Euler equations,the synergy relationship between the velocity field and the pressure gradient field in the pipe is derived,and the synergy evaluation of airflow noise reduction is proposed;The influence of factors such as the inlet velocity of the branch pipe,the shape of the pipe section,the cross-sectional aspect ratio,the distance between the branch pipes,and the relative position on the flow field and the sound field in the pipe are discussed;By modifying the synergistic relationship between the velocity field and the pressure gradient field in the tube,the structure optimization of the confluent T-elbow pipelines was carried out,and the noise reduction design was completed.The research results show that the downstream section of the main pipe is the source of aerodynamic noise for the confluent T-elbow pipelines;the synergy between the velocity and the pressure gradient in the pipe is related to the strength of the aerodynamic noise,and the velocity vector the smaller the angle between the pressure gradient and the pressure gradient,the smaller the amplitude of the dipole sound source generated by the airflow manifold.The aerodynamic noise of the confluent T-elbow pipelines is most affected by the flow velocity of the branch,followed by the section shape and section width height ratio,and the spacing of the branch and the placement of the branch are less affected.Based on the synergy angle and streamline distribution,the end structure of the confluent T-elbow branch pipe and the inflow angle of the Y-shaped tee are optimized,and the effect is remarkable. |
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