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.
In this paper, four typical compounds of odorants were selected as the research objects. The mathematical model hypothesis is established which based on the Weber-Fechner law, and then the relationship between the concentration of odor substances and the odor grade is verified to judge whether this law is applicable to the objective evaluation of vehicle interior odor. The results show that: the concentration of single odor substance and odor grade, the concentration of two kinds of odor substances and odor grade are in accordance with this law. It is proved that the relationship between odor substance concentration and odor grade conforms to the law to a certain extent, which provides an important theoretical basis for objective evaluation of vehicle interior odor and control vehicle environment to create an environmental and healthy vehicle.
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