氢气非预混燃烧的流场输运特性分析

Transport Characteristics of Flow Field in Hydrogen Non-Premixed Combustion

采用高精度直接数值模拟的方法对氢气非预混燃烧流场进行了精细的预测.模拟所求解的控制方程为三维可压缩的无量纲形式的Navier-Stokes方程,采用六阶精度紧致差分格式,结合基于详细化学反应和输运过程的FGM化学反应机制,利用768个处理器核、共近4.53亿网格点进行了基于CPU的大规模高效并行计算,分析氢气非预混燃烧特性,并进一步探讨了浮力对氢气燃烧流场输运特性的影响.研究发现,由于氢气燃烧过程中产生不同扩散性质的化学组分,使燃烧过程中遵循优势扩散的行为.这将影响流场的输运特性和火焰不稳定性的形成.在浮力驱动的氢气优势扩散燃烧流场中,对流是质量、动量及热量输运行为的主要影响因素,而无浮力火焰中优势扩散主导着流场的输运特性.平均统计结果表明,有浮力和无浮力的燃烧流场中都可以捕捉到逆梯度输运现象,且浮力会促进逆梯度输运行为的发生.

The high-precision direct numerical simulation method was used to accurately predict the flow field in hydrogen non-premixed combustion.The governing equations obtained by the simulation were Navier-Stokes equations of three-dimensional compressible dimensionless forms.The sixth-order precision compact difference format was used,the FGM chemical reaction mechanism based on detailed chemical reaction and transport process was employed,and a large-scale and efficient CPU-based parallel computing was performed using 768 processor cores and nearly 453 million grid points.The non-premixed combustion characteristics of hydrogen were analyzed,and the influence of buoyancy on the transport characteristics of hydrogen combustion flow field was further discussed.Studies show that chemical components with different diffusion properties are produced during the combustion of hydrogen,which leads to the preferential diffusion behavior in the combustion process.It will affect the transport properties of the flow field and the formation of flame instability.Convection is the main influencing factor of mass,momentum and heat transport in the buoyancy-driven hydrogen preferential diffusion combustion flow field,while the preferential diffusion in the buoyancy-free flame dominates the transport characteristics of the flow field.The average statistical results show that the counter-gradient transport phenomenon can be captured in both buoyancy and buoyancy-free combustion flow fields,and buoyancy will promote the occurrence of counter-gradient transport behavior.