风管隆隆声通常归因于风机出口不良的空气动力排放条件。到目前为止，定性描述符已被用作工程师限制管道隆隆噪声量的指南。本研究的目的是创建并验证一个测试设备，该设备将准确量化风机和风管系统排放条件变化引起的风管隆隆噪声量。然后，有效数据将用于用定量预测取代定性描述。测试系统的一个关键设计约束是检测因风扇排气配置而产生的声音变化。试验设备能够在14种不同的排放条件之间进行切换。 有四种不同的风机方向:一个处于前风状态的风机直接吹入管道系统，一个向上吹向肘部的风机，一个向上吹向肘部的风机，一个向上吹向肘部的风机，以及一个向上吹向肘部的风机。每一个都是在距管道入口不同距离的风扇出口处测量的。“最佳”或前吹气流在风扇和进气口之间有两个距离，其余方向在风扇和进气口之间有四个距离。风机在分布在风机工作范围内的八个工作点上运行。管道和测量系统的设计便于测量和验证风扇排放条件的声压级影响。 声音测量是在16到300赫兹之间的三分之一倍频带上进行的。窄带分析的频率高达800 Hz。测量是在一个隔音房间内的九个位置和管道系统中的七个位置进行的。测量精度在±1dB范围内，远低于风扇配置引起的3至11 dB变化。分析结果的目的是基于数据建立数学关系，这些数据可用于估计声功率的变化，作为流速、风机压降、风机方向、风机出口到弯头过渡段的距离和频率的函数。结果表明，这种相关性比多重相关性更复杂- 变量多项式模型。综上所述，所有结果表明，需要进一步对风机的入口和出口流动条件进行更详细的分析。单位:I-P

Duct rumble noise is commonly attributed to the poor aerodynamic discharge conditions of fan outlets. Thus far, qualitative descriptors have been used as guidelines for engineers to limit the amount of duct rumble noise. The objective of this study was to create and verify a test facility that would accurately quantify the amount of duct rumble noise that was caused by the change in discharge conditions of a fan and duct system. Valid data will then be used to replace the qualitative descriptor with quantitative predictions. A key design constraint of the testing system was detecting the change in sound due to the fan discharge configuration.The test facility was capable of changing between fourteen different discharge conditions. There were four different fan orientations: a fan in front blast condition blowing directly into the duct work, a fan in upblast with rotation towards the elbow, a fan in upblast rotating with the elbow, and a fan upblast rotating against the elbow. Each of these was measured with the fan outlet at different distances away from the duct inlet. The "optimum" or frontblast had two distances between the fan and inlet, the rest of the orientations had four distances between the fan and the inlet. The fan was operated at eight operating points distributed over the fan operating range. The duct and measurement system was designed to easily measure and verify the sound pressure level effect of the fan discharge conditions.The sound measurements were taken at one-third octave bands between 16 and 300 Hz. The narrow band analysis was taken up to 800 Hz. The measurements were taken in an acoustically isolated room at nine locations in the room and seven locations in the ductwork. The accuracy of the measurement was within ± 1dB, which was far less than the 3 to 11 dB variations that are caused by the fan configuration.The results were analyzed with the goal to develop mathematical relationships based on the data that could be used to estimate the change in sound power as a function of flow rate, pressure drop across the fan, fan orientation, distance of the fan outlet to the elbow transition, and frequency. The results show that the dependence is more complex than a multi-variable polynomial model. Taken together, all the results suggest that future work is needed for more detailed analysis of the inlet and outlet flow conditions of the fan.Units: I-P