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大涡模拟中的条件滤波耗散和扩散的统计特性

Statistics of conditionally filtered dissipation and diffusion in large eddy simulation

  • 摘要: 当大涡模拟用于研究化学反应流动时,传统的滤波方法会导致化学反应项不封闭. 为克服这个困难,发展了条件滤波大涡模拟方法. 在选择适当的条件变量后,条件滤波的化学反应项可以表达为一个封闭项. 但同时也带来了新的问题:条件滤波耗散或条件滤波扩散项的不封闭. 为解决这一问题,采用了直接数值模拟方法研究了它们在大小尺度上的统计特性. 研究结果表明:条件滤波耗散和扩散对于大尺度的依赖主要体现在大尺度标量场中扩散层结构的影响,同时小尺度脉动的变化几乎与条件滤波扩散无关,而它对条件滤波耗散却显现出明显的作用. 在构造条件滤波耗散的亚格子模型时,小尺度脉动的作用不容忽视.

     

    Abstract: In the large eddy simulation of turbulent reacting flows, thefiltered reaction terms are unclosed. It is difficult to construct thesubgrid scale (SGS) model for filtered reaction terms due to the absenceof a universal energy cascade process, which is the foundation of SGS modelsin fluid turbulence. With the conditional filter approach, theSGS models for conditionally filtered reaction terms can be closed, butconditional diffusion and dissipation have to be modeled. We use a directnumerical simulation of turbulent mixing to investigate the scale-dependenceof the conditional filtered diffusion and dissipation. The results show that theconditional filtered diffusion depends on large scales, but the conditionalfiltered dissipation depends on both large and small scales. The effectsof small scales on the conditional filtered dissipation have to be includedin its SGS models.

     

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