基于湍动能谱的自适应大涡模拟方法

Adaptive Large Eddy Simulation Based on Energy Spectrum

关键词:  大涡模拟  自适应  湍动能谱  跨尺度算法  湍流燃烧 

Key words:  Large eddy simulation  Adaptive  Energy spectrum  Trans-scale algorithm  Turbulent combustion

摘要:

为了在计算量有限的前提下实现对不同尺度上湍流燃烧结构的直接求解,提出了新的基于湍动能谱的自适应大涡模拟的概念。在这一概念下,利用湍动能谱和自适应网格技术建立了跨尺度算法,从而实现DNS和LES两种方法的耦合。在湍流非预混氢气射流火焰的模拟中,该方法既能捕捉大尺度湍流结构,又能分辨小尺度燃烧结构,计算出的物理量的瞬态和时均分布和DNS结果吻合得较好。计算偏差主要体现在DNS和LES区域的过渡处,这与亚格子湍动能在过渡处的变化不够平滑有关,表明跨尺度算法需要优化,以完善对不同尺度间湍动能传输的模拟。 

Abstract:

In order to directly resolve turbulent combustion at different scales with acceptable computational expenditure, a new method called Energy Spectrum Based Adaptive Large Eddy Simulation was proposed. A trans-scale algorithm based on energy spectrum and dynamic adaptive mesh technology was developed for this method to couple DNS and LES. It is shown in the simulation of a turbulent nonpremixed hydrogen jet flame that this method can resolve the turbulent coherent structures at large scales as well as the combustion structures at small scales. It is validated with good agreement on transient and temporal-average distribution of physical quantities between this method and DNS. The computational deviations of this method in the transition region between DNS and LES regimes are greater than those in other places. This is because the variation of sub-grid turbulent kinetic energy in the transition region is not sufficient smooth, indicating that the trans-scale algorithm has to be optimized for a better simulation of turbulent kinetic energy cascade between different scales. 