Abstract A detailed numerical investigation of temperature effects on both aerodynamics and acoustics of a dual-stream jet including a central plug is carried out. The geometry is representative of a realistic turbofan with a high by-pass-ratio (BPR) close to 9. Two take-off high-subsonic operating points are investigated numerically by compressible large-eddy simulation. For these two selected points, the secondary stream is exactly the same in terms of static temperature and velocity. Both jets have also the same primary velocity. The only difference lies in the static temperature of the primary jet. There is a ratio of two between the two jets considered in this study, namely T j = 400 K and T j = 800 K. More precisely, the primary jet temperature is reduced while keeping the acoustic Mach number constant, leading to an increase of the primary jet Mach number from M j = 0.65 in the heated case to M j = 0.89 in the cold case. Some experimental data are available for the hot jet while the cold jet is introduced for academic reasons. The heated jet compares reasonably well with the experimental data, taking into account the complexity of the geometry. Temperature effects have a limited impact on aerodynamic development and acoustic radiation. The influence of the core flow is found to be weak due to the high BPR considered and the radiated acoustic is mainly driven by the secondary flow. Further investigations are carried out in order to highlight the differences between the two cases. The acoustic production area are identified by the way of axial velocity skewness coefficient maps. Finally, a decrease of the primary stream temperature leads to the development of trapped acoustic waves inside the jet core. An increase of the overall sound spectrum level about 5 dB is thus observed in the upstream direction for the cold jet, in agreement with the vortex sheet theory.

中文翻译：

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温度对真实亚音速双流射流噪声源机制的影响

摘要 对包括中心塞的双流射流的空气动力学和声学的温度影响进行了详细的数值研究。该几何结构代表了具有接近 9 的高旁通比 (BPR) 的现实涡扇发动机。通过可压缩大涡模拟对两个起飞高亚音速工作点进行了数值研究。对于这两个选定的点，次级流在静态温度和速度方面完全相同。两种射流也具有相同的初级速度。唯一的区别在于主射流的静态温度。本研究中考虑的两个射流之间的比率为 2，即 T j = 400 K 和 T j = 800 K。更准确地说，主射流温度降低，同时保持声学马赫数不变，导致主射流马赫数从加热情况下的 M j = 0.65 增加到冷情况下的 M j = 0.89。一些实验数据可用于热射流，而冷射流因学术原因而引入。考虑到几何形状的复杂性，加热射流与实验数据相当好。温度效应对空气动力学发展和声辐射的影响有限。由于考虑了高 BPR，发现核心流的影响很弱，并且辐射声主要由二次流驱动。进行了进一步调查以突出两个案例之间的差异。通过轴向速度偏度系数图的方式识别产声区。最后，主流温度的降低导致在喷射核心内产生捕获的声波。因此，在冷射流的上游方向观察到整体声谱级增加约 5 dB，与涡片理论一致。