Architectural Engineering Program, University of Nebraska-Lincoln, 1110 South 67th Street, Omaha, Nebraska 68182-0681, USA.
J Acoust Soc Am. 2009 Dec;126(6):3028-39. doi: 10.1121/1.3257209.
Numerical and experimental studies were undertaken to characterize the noise transmission and scattering properties in higher-order modes across the tee-junction of a rectangular duct used in ventilation and air-conditioning systems. To measure these properties, a formulation of a transmission matrix based on the transfer function and a two-microphone method was devised. The measurement of modal sound transmission and scattering coefficients is demonstrated for a duct element in a rectangular duct. The results of numerical simulations were verified by experiments. The results show that sound transmissions of fundamental mode and higher-order modes across the main duct are high at the eigen-frequencies of the main duct and sidebranch. Weak modal coupling of the branch-modes and the traveling wave in the main duct is observed at or very close to the eigen-frequencies of the sidebranch, which shifts excitation of the higher-order branch-modes at higher frequencies. A decrease in sound transmission and increase in sound scattering into higher-order modes occur with excitation of the axial branch-mode. Excitation of the longitudinal branch-mode due to branch-end reflection also results in lower sound transmission of higher-order modes across the junction along the main duct.
进行了数值和实验研究，以表征通风和空调系统中矩形管道的三通接头中高阶模式的噪声传输和散射特性。为了测量这些特性，设计了一种基于传递函数和双麦克风方法的传输矩阵公式。对矩形管道中的管道元件进行了模态声传输和散射系数的测量。数值模拟结果通过实验得到验证。结果表明，在主管道的本征频率处，基本模式和高阶模式的声传输在主管道和分支管道中都很高。在分支管道的本征频率处或非常接近该频率处，可以观察到分支模式的模态耦合和主管道中的行波很弱，这会将高阶分支模式的激励转移到更高的频率。随着轴向分支模式的激励，声传输减少，高阶模式的声散射增加。由于分支端反射激励的纵向分支模式也会导致高阶模式在主管道沿线的连接处的声传输降低。
