Modeling of the mechanism of appearance of external infrasound of land vehicles

Abstract

The main contribution to the acoustic pollution of residential areas is made by land vehicles including automobiles. Most scientific publications are devoted to the study of audible sound, its sources in the vehicle and the development of measures to reduce it. According to the authors opinion, at present the problem of the emergence and spread of infrasound in residential areas, and, accordingly, its negative impact on people and the environment is underestimated. Hence the development of computational and experimental methods for studying the mechanism of the appearance of infrasound from a vehicle is a very urgent problem. A large proportion of the acoustic radiation from the vehicle falls on infrasound and low-frequency range of frequencies. Depending on the design of the automobile, the occurrence of internal infrasound can be caused by the engine's vibrations as a rigid body on its suspension, flexural and torsional body oscillations, the impact of the oncoming airflow. Measurements of internal and external infrasound were carried out. A computational model is proposed and an assessment is made of the influence of the design features of the vehicle on the level of infrasound. Calculation studies of the mechanism of the appearance of an external infrasound of a vehicle have shown that its frequency and level depend on the speed of movement, the drag coefficient, the length and the Strouhal number. A significant source of infrasound in the automobile are also wheels that perform rotational and translational movements in the oncoming air stream. Calculation of five wheel harmonics for a automobile at various speeds of movement is carried out, existing dependences are revealed. The results of the calculation showed that exceeding the normative values of infrasound is possible only in residential areas adjacent to the traffic flow with speeds of over 80 km / h.