可变密度射流的大涡模拟及相干结构研究

Large Eddy Simulation and Coherent Structure Analysis of Variable-Density Jets

摘要

密度变化是影响变密度射流混合特性和流动稳定性的关键因素。针对氦气、空气和二氧化碳这 3 种来流气体（与空气密度比分别为 0.14、1.00 和 1.52）所形成的变密度射流，在射流动量通量相同的条件下，采用大涡模拟方法研究射流平均流场、涡结构以及相干结构的演化过程。结果表明，氦气射流的速度和浓度衰减较快，空气射流次之，二氧化碳射流衰减缓慢。采用 判据识别流场中的涡结构，发现氦气射流的涡结构失稳早、破碎快、涡团尺度大且径向扩散迅速；二氧化碳射流的涡结构稳定、破碎晚、涡团尺度小且径向分布集中；空气射流的涡结构则介于两者之间。在此基础上，对变密度射流的压力场进行动态模态分解和本征正交分解，结果表明二氧化碳射流的相干结构稳定；氦气射流的相干结构不稳定，从而导致其涡结构更易失稳破碎。此外，氦气射流中的波包结构是其卷吸速率较高的原因。

Abstract

Density variation is a key factor affecting the mixing characteristics and flow stability of variable-density jets. For variable-density jets where three types of gases (helium, air and carbon dioxide) are injected into ambient air with density ratios of 0.14, 1.00 and 1.52 respectively, large eddy simulation (LES) is adopted to investigate the evolution of mean flow fields, vortex structures and coherent structures under identical inlet momentum flux. The results reveal that the velocity and concentration of the helium jet decay rapidly, followed by the air jet, while the carbon dioxide jet exhibits slow decay of velocity and concentration. Vortex structures in the flow field are identified using specific criteria. It is found that the vortex structures of the helium jet become unstable and break up earlier, with larger vortex scales and faster radial diffusion. In contrast, the vortex structures of the carbon dioxide jet remain stable, break up later, feature smaller vortex scales and show concentrated radial distribution, and the vortex structures of the air jet lie between the two cases. On this basis, dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) are performed on the pressure field of variable-density jets. The results indicate that the coherent structures of the carbon dioxide jet are stable, whereas those of the helium jet are unstable, which makes its vortex structures more prone to instability and breakup. Furthermore, the wave packet structures in the helium jet account for its high entrainment rate.

关键词

变密度 / 射流 / 大涡模拟 / 相干结构 / 动态模态分解 / 本征正交分解

Key words

variable-density / jet / large eddy simulation / coherent structures / dynamic mode decomposition / proper orthogonal decomposition

参考文献

[1] VIGGIANO B, DIB T, ALI N, et al. Turbulence, entrainment and low-order description of a transitional variable-density jet[J].Journal of Fluid Mechanics, 2018, 836:1009-1049.

[2] SALIZZONI P, VAUX S, CREYSSELS M, et al. Entrainment in variable-density jets[J].Journal of Fluid Mechanics, 2024, 995:A11.

[3] KUAN T W I, SZMELTER J. Explicit and implicit large eddy simulations of variable-density low-speed flows[J].Journal of Computational Physics, 2024, 499:112715.

[4] RENZE P, SCHRODER W, MEINKE M. Large-eddy simulation of film cooling flows with variable density jets[J].Flow, Turbulence and Combustion, 2008, 80(1):119-132.

[5] FOYSI H, MELLADO J P, SARKAR S. Large-eddy simulation of variable-density round and plane jets[J].International Journal of Heat and Fluid Flow, 2010, 31(3):307-314.

[6] WAWRZAK K, BOGUSLAWSKI A. Self-excited oscillations in variable density counter-current round jets[J].International Journal of Heat and Fluid Flow, 2023, 103:109178.

[7] IVASHCHENKO V, RYZHENKOV V, MULLYADZHANOV R. Large-eddy simulations of variable-density turbulent jets[C]//Journal of Physics: Conference Series. [s.l.]: IOP Publishing,2018, 1128(1):012016.

[8] 刘琪麟, 赖焕新. 非等温喷流中波包的运动学分析 [J].工程热物理学报, 2023, 44(12):3272-3282.

[9] SHARMA A, DE A, KUMAR S. Investigation of injector-coupled combustion dynamics in a methane-oxygen combustor using large eddy simulation and dynamic mode decomposition[J].Physics of Fluids, 2024, 36(6):065116.

[10] QIANG L I U, ZHENBING L U O, XIONG D, et al. Numerical investigation on flow field characteristics of dual synthetic cold/hot jets using POD and DMD methods[J].Chinese Journal of Aeronautics, 2020, 33(1):73-87.

[11] CHAI X, IYER P S, MAHESH K. Numerical study of high speed jets in crossflow[J].Journal of Fluid Mechanics, 2015, 785:152-188.

[12] ROVIRA M, ENGVALL K, DUWING C. Proper orthogonal decomposition analysis of the large-scale dynamics of a round turbulent jet in counterflow[J].Physical Review Fluids, 2021, 6(1):014701.

[13] BOGEY C, BAILLY C. Effects of inflow conditions and forcing on subsonic jet flows and noise[J].AIAA Journal, 2005, 43(5):1000-1007.

[14] DJERIDANE T, AMIELH M, ANSELMET F, et al. Velocity turbulence properties in the near‐field region of axisymmetric variable density jets[J].Physics of Fluids, 1996, 8(6):1614-1630.

[15] 欧玉琼, 刘琪麟, 赖焕新. 中低雷诺数可压缩冲击射流的流动与传热特性 [J].华东理工大学学报 (自然科学版), 2025, 51(3):419-427.