基于一维全尺度湍流模型的氢气射流扩散火焰结构数值模拟

One-Dimensional Turbulence Simulation of Diffusion Flame in a Hydrogen-Air Jet with Detailed Chemistry

基于Kolmogorov涡旋理论,建立了随机涡旋特征时空尺度及发生频率分布数理模型,在求解动量、组分和能量层流边界层方程的同时,对随机涡旋进行物理概率意义上的模拟．化学反应采用23步氢气氧化详细机理．控制方程组数值求解时,时间积分采用Williamson发展的三阶精度、全显式、低存储Runge-Kutta法,空间离散采用类谱高精度Padé紧致差分格式．结果表明,高精度数值离散格式能更好表达湍流小尺度的时空结构．运用一维全尺度湍流模型对氢气湍流射流扩散火焰结构进行计算研究,模拟结果充分展示了湍流涡旋串级现象,表明湍流涡旋对标量混合具有重要影响,涡旋增强了燃料和氧化剂之间的湍流输运,强化了混合,从而大大影响湍流燃烧速率．

This paper presents the results of a detailed study of one-dimensional turbulence （ODT） to a jet flame. The approach is based on the mechanistic distinction between molecular processes （reaction and diffusion）, and implemented by the direct solution of unsteady boundary-layer reaction-diffusion equations and the stochastic process of turbulent advection in a time-resolved simulation on a 1D domain which corresponds to a direction transverse to the mean flow of the jet. A 23- step chemical mechanism is used to predict rates of reaction in hydrogen-air mixtures. Considering that all the relevant scales are required to be properly represented in ODT simulation, the governing equations are integrated forward in time using a third-order compact-storage fully explicit Runge-Kutta scheme developed by Williamson, and spatial differentiation is obtained by using the high-order compact （Padé） finite-difference scheme with spectral-like resolution. It is found that the schemes used here provide a better expression of the shorter space and time scales compared to the previous finite difference approximations performed in ODT studies. Two-dimensional renderings of stirring events from a single realization show that ODT reproduces a number of salient features of this developing turbulent shear flows that reflect the growth of the boundary layer and the mechanisms of turbulent cascade and spatial intermittency. Moreover, chemical properties of interest can be captured by the method. The results also show strong differential diffusion effects in the near field, with attenuation farther downstream.