基于CFD的天然气管道混气扩散规律研究

Research on natural gas pipeline mixing-flow properties based on computational fluid dynamics

随着我国多气源天然气市场发展和整体供气管网的形成,多气源直接接入管网混输已成为必然,不同气质气源直接管道混气的技术问题亟待研究和解决。基于CFD模拟,对不同气源混合输运的气质扩散规律进行研究,为混输管网合理设计和准确设定气质监控点提供依据,以保证燃气管网系统的安全可靠运行。重点对典型混气管路(Y型管)的天然气气质扩散规律进行数值模拟,获得掺混流体剪切层质量传递特征和天然气气质扩散规律。根据混气湍流形态和质量浓度场分布特征,获得Y型管的三类混气类型。通过对气质扩散质量浓度的不均匀性理论分析和模拟结果的综合数据分析,建立了预测混气管道达到气质均匀的混合长度无因次准则方程,为工程设计提供理论方法和计算基础。

With rapid development of natural gas markets and supplying resources in China, the national-wised mutual connection of variousgas suppliers to local distribution grids and supplying of multiple gas sources with different quality specificationsto consumers will appear unavoidably in the near future. To meet the gas interchangeability requirement and control the supplied gas quality specification have become one of the most important issues for the multi-source gas transportation and distribution. The gas property distribution in a Y-type mixing pipeline with two different gases was investigated by means of the computational fluid dynamics simulation. The mixing flow shear layer mass diffusion behaviors and the gas quality mixing and transport distances were analyzed to provide the theoretical basis forthe mixing pipeline design and setting thelocation of the gas qualitymonitory point at which the correct and reliable sampling gas quality can be ensured. The numerical simulation reveals the mixing flow shear layer and turbulent mass transport patterns for different inject flow velocity ratios and inject angles, and according to the patterns, the concentration distribution of the gaseous mixtures and the uniformity of the gas quality along the mixing flow pipeline were analyzed and formulated with the transport analogy theory. A dimensionless formula, which takes into account of the inject flow velocity ratio, inject angle and Reynolds number, was developed for the prediction of the mixing distance for uniform mixing of gases, and successfully correlated with the numerical simulation results.