F-packing 参数

F-packing 算法用来消除流动过程产生的小空泡或由较大的自由液面破碎形成的泡沫。它可以用来计算内部流体空间产生的负离散，其流体体积分数小于 0.99。它只可用在产生自由表面的单向流中。

The F-packing algorithm is used to eliminate small voids or “foaming” in flows with significant free-surface breakup. The algorithm works by creating small negative divergences in internal fluid cells, in which the fluid fraction is less than 0.99. It is only used in one-fluid flows with free surfaces.

F-packing 算法可以通过以下方式激活，Numerics > Volume-of-fluid advection > Advanced options > F-packing，如图所示。

The F-packing algorithm is activated by choosing one of the three options in Numerics > Volume-of-fluid advection > Advanced options > F-packing that activate the model.

默认设置是最佳的选择，适用于所有类型的流体。

No f-packing 就是完全关闭模式，默认是针对那种流动不受受突体扰动的情况（一般也不会产生空泡，实际是突体扰动有助于水流强迫掺气，产生空泡）。如果针对受突体扰动的水流不关闭空泡有可能造成一种非正常的现象。

close up interior voids，从选项就可以看出是将内部空泡关闭，这就确保了 f-packing 模式一直开启（这种模式针对那种水流表面受扰动情况下的单相流）。

By default, Default f-packing is selected: this is the optimal setting for all types of flow. Selecting No f-packing completely turns off the model and is the default for flows without sharp interfaces. For one fluid, sharp interface flows, however, this can cause unphysical voids to open up within the flow. The option Close up interior voids is selected, it ensures that the F-packing model is always turned on.

F-packing 的比率与系数成比例。默认值为 1。当设置为 0 则没有 packing 发生。

偶然情况下，由于 f-packing 的开启造成的压力改变会大大影响主流。这种情况一般出现在那些在某特定位置的流速和压力（例如随来流变化的水跃跃首），其值会偏离实际。在这种情况，减小 f-packing 系数（FLOW3D 中简称为cfpk）就显得尤为重要。

The rate of F-packing is proportional to the F-packing coefficient. The default value is 1.0. When it is equal to 0.0 no packing will take place. Occasionally, pressure changes due to F-packing may significantly interfere with the main flow. An indication of such situation can be a “run away” pressure and/or velocity at a location in the flow, which is out of range of physically meaningful values. In that case a smaller value of the F-packing coefficient may be necessary.

fluid fraction cleanup 值控制了孤立液滴（不足一网格时 ）发生。这种液滴的出现会造成 CPU 计算长时间且模拟不精准。默认值为 0（没有液滴移除）；当设定值大于 0 时，计算的过程中会丢弃液滴所占网络单元小于设定值的情况。建议此参数设定最好不要超过 0.05，否则会造成流体的减少。

The Fluid fraction cleanup value controls what FLOW-3D does when isolated fluid droplets (i.e., fluid occupying less than one cell) occur. The presence of such droplets can cause excessively long CPU times without adding to the accuracy of the simulation.The default value is 0.0 (i.e., no droplets removed); values greater than this will throw away such droplets when the fluid fraction within a computational cell is less than the prescribed value. This value should not be set greater than 0.05 or else excessive fluid volume loss can occur.

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