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[交流] ANSYS CFX14.5离散格式已有1人参与

请问一下各位，ANSYS CFX14.5非定常计算求解中空间离散和时间离散格式都是什么呢？？？

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致力航空，心系国防

1楼 2014-05-28 20:14:59

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时间有点长，本来还是了解一些的，今天仔细看了一下，忘记的太多了，希望下面的东东对你有帮助，对于空间离散，其实很简单，就是基于把N-S方程基于网格离散化，我截取一段，CFX的内容考过来没公式，你去看一下帮助（详细介绍查cfx帮助）；里面有一大章节讲的是这个。
Discretization of the Governing Equations
ANSYS CFX uses an element-based finite volume method, which first involves discretizing the spatial domain using a mesh. The mesh is used to construct finite volumes, which are used to conserve relevant quantities such as mass, momentum, and energy. The mesh is three dimensional, but for simplicity we will illustrate this process for two dimensions

关于时间离散，我不记得具体应该怎么解释了，你也看一下帮助吧，我也把部分内容截给你看，我看了一下，觉得没怎么解释的太明白，所以不好在这里给你瞎解释，你自己参考一下。
11.1.1.8. Transient Term

For control volumes that do not deform in time, the general discrete approximation of the transient term for the nth time step is:
(11–35)
where values at the start and end of the time step are assigned the superscripts n+½ and n-½, respectively.
With the First Order Backward Euler scheme, the start and end of time step values are respectively approximated using the old and current time level solution values. The resulting discretization is:

(11–36)
It is robust, fully implicit, bounded, conservative in time, and does not have a time step size limitation. This discretization is, however, only first-order accurate in time and will introduce discretization errors that tend to diffuse steep temporal gradients. This behavior is similar to the numerical diffusion experienced with the Upwind Difference Scheme for discretizing the advection term.
With the Second Order Backward Euler scheme, the start and end of time step values are respectively approximated as:

(11–37)

(11–38)
When these values are substituted into the general discrete approximation, Equation 11–35, the resulting discretization is:

(11–39)
This scheme is also robust, implicit, conservative in time, and does not have a time step size limitation. It is second-order accurate in time, but is not bounded and may create some nonphysical solution oscillations. For quantities such as volume fractions, where boundedness is important, a modified Second Order Backward Euler scheme is used instead.

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