The sound field radiated by noise sources in a cylindrical flow duct is so complicated that it has not yet been solved analytically. This paper presented a numerical method that was verified experimentally to predict the sound field. Figures are given for the direction coefficients of the sound pressure level (SPL) outside the duct for engineering applications. The figures can be used to easily calculate the sound power level of the sound source inside the duct through measuring the SPL at a single point outside of the duct. The sound field was numerically simulated using the linearized Euler equations, a fourth-order MacCormack finite difference scheme and Tam and Webb's non-reflection boundary conditions. The experiments in a semi-anechoic room used a scanning sound intensity meter to measure the sound power inside the duct and the sound pressure distribution outside the duct. The numerically determined SPL direction coefficients agree well with the measured data, with a maximum error within 1 dB.

首先给出吸气管道内噪声源辐射声场和管道入口流场的数值计算方法,再进行试验考核,最后给出辐射声压的指向性系数图.利用这些图就可方便地得到吸气管道内风机辐射声功率级和声压级的关系.