Study of Dual-Jet Interference and Scalar Mixing using Direct Numerical and Large-Eddy Simulations

本文采用大涡模拟（LES）和直接数值模拟（DNS）研究了不同形状喷管双射流和双标量的湍流干涉。该研究课题代表了湍流热、质量和流体流动领域的复杂多尺度物理现象，在机械、化学和环境工程中有着广泛的应用。例如，关于射流和标量的湍流混合的知识对于设计战斗机的高效双射流发动机排气和车辆的双消声器是至关重要的。动量和标量的输运过程（被动或主动）由许多因素决定，如喷嘴形状、喷嘴间距、雷诺数、施密特数、格拉肖夫数以及羽流和湍流涡旋的长度尺度。此外，通过动态演变的双射流界面，分离的瞬时湍流和非湍流（T/NT）流动区域的吞没和夹带过程中发挥了重要作用的湍流混合过程。 这项研究的长期目标是获得深入的知识湍流干扰射流和标量混合的物理，以提高我们的湍流理论的基本理解，以及在工程应用中的实际技能，并开发高保真度的模拟工具，提高湍流现象的数值预测。第一个短期目标侧重于研究从不同形状喷嘴发出的双射流的干扰。二维和三维射流将进行测试，从平面，圆形和同心圆喷嘴，并从椭圆形和矩形喷嘴不同的纵横比。双射流的LES结果将分别与高雷诺数和低雷诺数下的实验和DNS数据进行比较。第二个短期目标包括一个更复杂的程度，由于使用主动标量而产生的额外体力。为此，将研究浮力射流，并研究浮力对动量和热能耦合传输的影响。第三个短期目标是开发和测试几种新的亚网格尺度模型，用于改进湍流和标量混合的LES预测。 拟议的研究将为申请人及其学生提供一个极好的机会，利用DNS和LES对双射流和双羽流的湍流干扰进行创新研究。所获得的先进知识和开发的数值工具，通过拟议的研究具有重要的理论和实用价值。拟议的研究还将提供一个宝贵的机会，在与数值建模，工程流体力学，传热和传质以及基于使用内部计算机代码和超级计算机的高性能科学计算相关的领域培训高素质人才。

In this research, turbulent interference of dual jets and dual scalars emitted from different shaped nozzles is investigated using large-eddy simulations (LES) and direct numerical simulations (DNS). This research subject represents a complex multi-scale physical phenomenon in the area of turbulent heat, mass and fluid flows, and has vast applications in mechanical, chemical and environmental engineering. For example, the knowledge on turbulent mixing of jets and scalars is critically important for designing highly-efficient twin-jet engine exhausts of a fighter aircraft and twin mufflers of a vehicle. The transport processes of momentum and scalars (passive or active) are determined by many factors such as the nozzle shape, nozzle separation distance, Reynolds number, Schmidt number, Grashof number, and length scales of the plumes and turbulent eddies. Furthermore, the engulfing and entrainment processes through the dynamically evolving dual-jet interfaces that separate the instantaneous turbulent and non-turbulent (T/NT) flow regions play a significant role in the turbulent mixing processes.     The long-term objective of this research is to obtain in-depth knowledge on the physics of turbulent interference of jets and mixing of scalars, to enhance our fundamental understanding of turbulence theory as well as practical skills in engineering applications, and to develop high-fidelity simulation tools for improved numerical prediction of turbulence phenomena. The first short-term objective focuses on a study of the interference of dual jets emitted from different shaped nozzles. Both 2D and 3D jets will be tested, emitting from planar, round and concentric circular nozzles, and from elliptic and rectangular nozzles of different aspect ratios. The LES results on dual jets will be compared against experimental and DNS data at high and low Reynolds numbers, respectively. The second short-term objective includes one more degree of complexity, an additional body force due to the use of active scalars. To this purpose, buoyant jets will be studied, and the effect of buoyancy on the coupled transport of momentum and thermal energy will be investigated. The third short-term objective is to develop and test several novel subgrid-scale models for improved LES predictions of turbulent flow and scalar mixing.     The proposed research will provide an excellent opportunity for the applicant and his students to conduct innovative research on turbulent interference of dual-jets and dual-plumes using both DNS and LES. The advanced knowledge gained and numerical tools developed through the proposed research are of significant theoretical and practical values. The proposed research will also provide a valuable opportunity to train highly qualified personnel (HQP) in areas related to numerical modelling, engineering fluid mechanics, heat and mass transfer, and high-performance scientific computing based on the use of in-house computer codes and supercomputers.