FLUENT的单精度和双精度求解器

2016-09-30 by:CAE仿真在线来源:互联网

单精度和双精度的区别:

单精度:具有7位精确小数位。

双精度:具有15位精确小数位。

另外,双精度需要占用两倍的内存空间,需要更长的时间完成计算。

看了一遍FLUENT帮助文件中对如何选择单精度和双精度求解器的说明:

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对大多数算例来说,单精度求解器已经足够精确。但是对以下几种情况,双精度求解器更适合:

1.流域具有显著的长度尺度(例如一根细长的管道),用单精度表示点坐标可能不够精确。

2.流域是几个区域,彼此之间用小尺寸的管道连接起来(例如汽车发动机歧气管),其中的一个区域的气压大大高于整个流域的平均水平,这种情况有必要用双精度方案来求解压差。

3.对于涉及到高的热传导率的共轭问题(共轭问题,我的理解是两个区域的相邻边界传热或者边界和区域内流体相互传热)、或网格单元的长宽高尺寸比率很大的网格(扁的或狭长的网格),单精度求解器不能有效地传递边界信息,会导致计算不收敛和不精确。

4.对于采用了population balance模式求解particle size分布可能包含数个数量级跨度的statistical moments的的多相流问题,适合用双精度求解器。(没用过population balance模式,完全不知道这一条什么意思 FLUENT的单精度和双精度求解器

)

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另外,我个人的经验,当计算瞬态问题的时间步长很小时,用双精度求解器可以获得更好的收敛性。

附:FLUENT帮助文件原文:

Single-Precision and Double-Precision Solvers

Both single-precision and double-precision versions of ANSYS FLUENT are available on all computer platforms. For most cases, the single-precision solver will be sufficiently accurate, but certain types of problems may benefit from the use of a double-precision version. Several examples are listed below:

If your geometry has features of very disparate length scales (e.g., a very long, thin pipe), single-precision calculations may not be adequate to represent the node coordinates.

If your geometry involves multiple enclosures connected via small-diameter pipes (e.g., automotive manifolds), mean pressure levels in all but one of the zones can be quite large (since you can set only one global reference pressure location). Double-precision calculations may therefore be necessary to resolve the pressure differences that drive the flow, since these will typically be much smaller than the pressure levels.

For conjugate problems involving high thermal-conductivity ratios and/or high-aspect-ratio meshes, convergence and/or accuracy may be impaired with the single-precision solver, due to inefficient transfer of boundary information.

For multiphase problems where the population balance model is used to resolve particle size distributions, which could have statistical moments whose values span many orders of magnitude.

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