Study on transmission characteristics and factors influencing T-elbow aerodynamic noise in ventilation and air-conditioning pipelines

Local ductwork components, such as shunt T-elbows, generate aerodynamic noise in ventilation and air-conditioning systems where turbulent air flow dissipates pulsation. The noise generated by airflow propagates along the ductwork to the end that terminates into a room. The incident acoustic energy may affect the working efficiency and health of the occupants. In this study, computational fluid dynamics and acoustic finite element methods were used to solve the Lighthill acoustic equation and simulate the flow field through T-elbows and the noise field generated by the airflow. The goal is to explore generation and transmission of aerodynamic noise through ductwork in a ventilation and air-conditioning system. The effects of inflow velocity, flow distribution ratio and T-elbow geometry on the noise intensity and acoustic energy propagation were investigated. The results show that low-frequency noises at the branch of the T-elbow are dominant and are caused by local unsteady vortex motion when the air flow diverges rapidly. In addition, the noise intensity and the propagated acoustic energy vary with the inflow velocity, branch flow rate ratio and branch geometry. Finally, the optimal structure for reducing noise in specific conditions can be determined by analysing and comparing various T-elbow geometries.