Renormalization Group-Based Transport Modeling of Premixed Turbulent Combustion. II. Finite Density Gradient and Direct Heat Release

A new method for numerical simulation of flame propagation in turbulent premixed combustible gaseous mixtures is proposed and tested. The method combines (I) a modified eikonal equation, employed to model the flame front dynamics; (2) a method of front tracking using a strip of computational cells containing the flame; and (3) a formula for turbulent flame propagation speed. The method includes two separate models. The first one obviates the necessity to solve equations for heat release, temperature and enthalpy, and utilizes a model equation of state to accurately render the volumetric effect and related instabilities. The second one provides a model for direct heal release and temperature calculation in the presence of heat-conducting boundaries (walls), in the multi-component combustible mixtures with variable composition and temperature-dependent heat capacities of all species. This model can be used when the heat transport on the walls is of interest, effects of flame quenching are essential and for the especially important case of combustion in a closed volume, e.g., in a cylinder of an internal combustion engine or chemical reactor. This modification is also effective for simulation of ramjet engines. The new method proves to be self-consistent, robust and highly effective.     

Two-Equation RNG Transport Modeling of High Reynolds Number Pipe Flow

New solutions of two-equation RNG turbulence transport model are used to calculate high Reynolds number pipe flows. The results are compared with experimental Superpipe data of Zagarola et al. (1996) up to Reynolds number of 3.5 × 10⁷.     

Renormalization group analysis of turbulence. I. Basic theory

We develop the dynamic renormalization group (RNG) method for hydrodynamic turbulence. This procedure, which uses dynamic scaling and invariance together with iterated perturbation methods, allows us to evaluate transport coefficients and transport equations for the large-scale (slow) modes. The RNG theory, which does not include any experimentally adjustable parameters, gives the following numerical values for important constants of turbulent flows: Kolmogorov constant for the inertial-range spectrumC _K=1.617; turbulent Prandtl number for high-Reynolds-number heat transferP _t =0.7179; Batchelor constantBa=1.161; and skewness factor¯S ₃=0.4878. A differentialK- model is derived, which, in the high-Reynolds-number regions of the flow, gives the algebraic relationv=0.0837 K²/ , decay of isotropic turbulence asK=O(t ^–1.3307), and the von Karman constant=0.372. A differential transport model, based on differential relations betweenK, , and, is derived that is not divergent whenK 0 and is finite. This latter model is particularly useful near walls.     

基于GML的公共交通数据建模

文章分析了目前的交通信息系统的建模方法及其存在的问题,结合GML3.1、GML模式和线性参考方法,研究了使用GML对公共交通数据模型的几何和拓扑关系建模的方法。以城市公共交通模型为开发实例,给出了基于GML的郑州市公共交通的建模方案和具体实现方法,并使用XSLT技术将最终结果可视化。     

群组通信模型及运输协议映射*

新型网络应用要求通信协议提供多点投递和相应群组管理功能,同时,高速传输服务和新型网络层协议也开始具有数据多点传输和简单群组控制能力,跨越两者的运输层协议,从而又重新成为学术研究和标准化的热点和趋势.文章主要描述建立群组通信抽象模型的过程和结论以及参照新型运输协议XTP(express transport protocol)和计算机会议应用的模型映射和评价.