Compact and non-compact analytical solutions of the subsonic operating point of the entropy wave generator experiment are compared with detailed numerical results obtained by large Eddy simulations. Two energy deposition methods are presented to account for the experimental ignition sequence and geometry: a single-block deposition as previously used and a delayed deposition that reproduces the experimental protocle closely. The unknown inlet acoustic reflection coefficient is assumed to be fully reflective to be more physically consistent with the actual experimental setup. The time delay between the activation of the heating modules must be considered to retrieve the temperature signal measured at the vibrometer and pressure signals at the microphones. Moreover, pressure signals extracted from the large Eddy simulations in the outlet duct using the delayed ignition model clearly reproduce the experimental signals better than the analytical models. An additional simulation with actual temperature fluctuations directly injected at the inlet of the computational domain clearly shows that the pressure fluctuations produced by the acceleration of the hot slug yields indirect noise almost entirely. Finally, the entropy spot is shown to be distorted when convecting through the turbulent flow in the entropy wave generator nozzle. Its amplitude decreases and its shape is dispersed, but hardly any dissipation occurs. The distortion appears to be negligible through the nozzle and become important only when convected over a long distance in the downstream duct. As the dominant frequencies of the entropy wave generator entropy forcing are very low, the effects of dispersion by the mean flow are however weak.

中文翻译：

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熵波发生器实验中间接燃烧噪声的大涡模拟预测

将熵波发生器实验的亚音速工作点的紧凑和非紧凑解析解与通过大型涡流模拟获得的详细数值结果进行了比较。提出了两种能量沉积方法来说明实验的点火顺序和几何形状：以前使用的单块沉积和延迟沉积，其紧密地复制了实验协议。假定未知的入口声反射系数是完全反射的，以在物理上与实际实验设置更加一致。必须考虑激活加热模块之间的时间延迟，以获取在振动计上测得的温度信号和在麦克风上的压力信号。此外，使用延迟点火模型从出口管道中的大型涡流模拟中提取的压力信号明显比分析模型更好地再现了实验信号。直接在计算域入口处注入实际温度波动的附加模拟清楚地表明，由热弹加速产生的压力波动几乎完全产生了间接噪声。最后，当通过熵波发生器喷嘴中的湍流对流时，熵点显示为扭曲的。其幅度减小并且其形状分散，但是几乎不会发生任何耗散。通过喷嘴的变形似乎可以忽略不计，并且仅在下游管道中长距离对流时才变得重要。