Direct Numerical Simulations and Large Eddy Simulations of Unpremixed Turbulent Flames

湍流非预混燃烧采用直接数值模拟和大涡模拟相结合的方法进行模拟。数值计算将采用谱配置(傅立叶变换)和谱单元(切比雪夫变换和P型有限元)技术。通过数值模拟，我们将研究以下物理问题：火焰尖端接近熄灭时的动力学，火焰上升的结构和渗流理论应用于火焰片“孔洞”的验证，以及在空间发展的湍流火焰中守恒标量的瞬时值与其耗散率之间的耦合。大涡模拟工作的目标是使用标量单点概率密度函数发展亚网格湍流闭合，并将其应用于经历有限速率二元反应的均匀湍流。本文主要研究放热反应对湍流的影响，谱元方法在可压缩反应湍流中的应用，大涡模拟在有限速率反应湍流中的应用。结果应该找出与目前使用的一些湍流模型相关的缺点，并指导改进的关闭技术，从而提高我们可靠地模拟更接近物理的燃烧室流动的能力。

Turbulent, nonpremixed combustion is to be modeled using a combination of direct numerical simulation (DNS) and large eddy simulation (LES) approaches. The numerics will employ spectral collocation (Fourier transforms) and spectral element (Chebyshev transforms and P-type finite elements) techniques. The following physical issues will be investigated through DNS: flame tip dynamics near extinguishment, lifted flame structure and the validation of percolation theory applied to flame sheet "holes", and the coupling between the instantaneous values of a conserved scalar and its rate of dissipation in spatially developing turbulent flames. The LES work will be aimed at developing a subgrid turbulence closure using a scalar single-point probability density function, with application to a homogeneous turbulent flow undergoing a finite rate binary reaction. The main objects of this research are the effects of exothermic reactions on turbulence, application of the spectral-element method to compressible reacting turbulent flows, and application of LES to finite rate reacting turbulent flows. The results should identify shortcomings associated with some of the turbulence models presently in use and guide the way to improved techniques for closure, thus advancing our ability to reliably model more physically realistic combustion chamber flows.