热粘性对发动机排气管道中噪声传播的影响

Effect of thermo-viscosity on noise propagation in engine exhaust pipe

声波在气体中传播时,气体的热粘性效应会使声波产生一定程度的衰减,且气体的声吸收系数随温度的升高而增大。由于发动机的排气温度较高,热粘性效应引起的排气管道中的噪声衰减应加以考虑。基于准平面波理论,首次计算了考虑热粘性效应时不同温度、流速和管道尺寸下排气管道中的传递损失,分析了各参数对管道中噪声衰减的影响。结果表明,随着温度和频率的升高热粘性声衰减增强,而气流流速和管道直径的增加会降低直管中的热粘性声衰减。对于简单膨胀腔,传递损失的预测结果表明,热粘性效应使通过频率处的声衰减有所改善。

The thermo-viscosity of gas can attenuate the sound waves in the propagation, and the sound absorption coefficient is increased with temperature. In view of the higher temperature of the engine exhaust gas, the effect of thermo-viscosity on noise attenuation in an exhaust pipe needs to be considered. Based on the pseudo-plane-wave theory, transmission losses （TL） of exhaust pipes are calculated for the first time for different temperatures, flow velocities and pipe dimensions. The results show that increasing the temperature and frequency can enhance the sound attenuation of a straight pipe caused by the visco-thermal effect, while the increase in the flow velocity and pipe diameter will reduce the sound attenuation. Prediction of TL of a simple expansion chamber demonstrates that the effect of thermo-viscosity improves the sound attenuation somewhat at the pass frequencies.