The lobed nozzle is usually used in the exhaust system of military helicopters to improve survivability. The thermal and flow characteristics of the lobed mixer with and without the scalloping structure are investigated to provide a theoretical basis. The delayed detached eddy simulation is used after validated against Hu's experiment of stereoscopic particle image velocimetry. The specific position, where the scalloping structure improves the mixing performance, is summarized. The dominant frequency of downstream vortex is quantitatively characterized by the power spectral density analysis. The results show that the scalloping structure brings a rapid improvement in the mixing performance near Z/D=0.75 and a faster mixing completion rate. At Z/D=1, the mixing efficiency of the scalloping structure is about 0.46 and the efficiency is enhanced by about 13.5%. The mixing characteristics correspond to the streamwise vortices with a larger spatial scale and stronger intensity in the downstream time-averaged flow field. In terms of unsteady flow, the downstream coherent structures include K-H vortex, hairpin vortex, streamwise vortex, normal vortex, and shedding vortex for the lobed mixer with the scalloping structure. Shedding vortices destroy the complete structure of the normal vortex. Meanwhile, shedding vortex enhances the vorticity intensity and spatial scale of streamwise vortices.

军用直升机的排气系统通常采用叶形喷口，以提高生存能力。研究了具有和不具有扇形结构的叶状混合器的热和流动特性，以提供理论依据。经胡氏立体粒子图像测速实验验证后，采用延迟分离涡模拟。总结了扇形结构提高混合性能的具体位置。下游涡旋的主频通过功率谱密度分析定量表征。结果表明，扇形结构在Z/D=0.75附近带来了混合性能的快速提升和更快的混合完成率。Z/D=1时，扇形结构的混合效率约为0。46，效率提高了约 13.5%。混合特性对应于下游时间平均流场中空间尺度更大、强度更强的流向涡旋。就非定常流而言，下游相干结构包括KH涡、发夹涡、流向涡、法向涡和扇形结构的叶瓣混合器的脱落涡。脱落的涡流破坏了正常涡流的完整结构。同时，脱落涡增强了流向涡的涡度强度和空间尺度。扇形结构的叶瓣混合器的流向涡、法向涡和脱落涡。脱落的涡流破坏了正常涡流的完整结构。同时，脱落涡增强了流向涡的涡度强度和空间尺度。扇形结构的叶瓣混合器的流向涡、法向涡和脱落涡。脱落的涡流破坏了正常涡流的完整结构。同时，脱落涡增强了流向涡的涡度强度和空间尺度。