在一些自由面流中，由紊流或流动条件改变（例如，冲击射流）造成空气卷入自由水面。掺气模型在模拟水流通过溢洪道，bottle filling（不知道该如何翻译，应该跟铸模有关）以及金属铸模的缺陷预测等方面从有着广泛的用途。
In some free-surface flows, gas may be entrained at the free surface due to turbulence or the flow conditions (e.g., an impinging jet). This has a wide variety of applications, from modeling the flow down a spillway, to bottle filling, and defect prediction in metal casting.
在FLOW-3D中，流体掺气可通过两相流模型或者使用了 Air entraiment模型的单向流来模拟。Air entrainment 通过Model Setup > Physics激活，通过平衡稳定力（重力和表面张力）和扰动力（紊动力）来预估流体中的掺气量（空泡区域）。Air entraiment 模型不仅包括了自由表面扰动产生的掺气，还包括了层流射入自由表面造成的掺气。因此，此模型在层流或者紊流中均可使用。当模拟紊流时，推荐使用k-ε双方程，RNG或者k – ω双方程模型。可通过Physics>Viscosity and Turbulence 激活，详细信息将在Turbulence（紊流）章节中讨论。
In FLOW-3D, the entrainment of gas can be modeled using the two-fluid model or, in one-fluid cases, by using the Air entrainment model. The Air entrainment model is activated on the Model Setup–>Physics tab and estimates the rate at which gas (represented by the void regions) is entrained into the flow using a balance of stabilizing forces (gravity and surface tension) and destabilizing forces (turbulence). Although the primary focus of the model is to compute the air entrainment resulting from turbulent disturbances at a free surface, the model also contains logic for handling entrainment resulting from laminar jets impinging on a free surface. Therefore, the model may be used for both laminar and turbulent cases. When modeling turbulent flows, the Two-equation , RNG or Two-equation turbulence models are recommended. These models can be activated in Physics →Viscosity and Turbulence and are discussed in more detail in Turbulence.
当使用 Air Entraiment 模型时，Entrainmet rate coefficient（含气率）必须设定为正。默认值为0.5，适合大多数情况下的初始设置。
同样可以设置流体的Surface tension coefficient（表面张力系数），包含以表面张力作为平衡力来定义掺气量的方式。这种情况下无需激活Surface tension模型。
When using the Air entrainment model, the Entrainment rate coefficient must be defined to be a positive value; the default value of 0.5 is a suitable starting point for most cases. The Surface tension coefficient for fluid can also be defined to include surface tension in the balance of forces defining the amount of entrained air. It does not activate the surface tension model.
基本模式下，掺气模型因不会影响流动，一般充当主流模型影响下的一种被动增加。当掺气量相对较小（<10%）时，显然是足够的。如果不是这种情况，则流动会受流体中掺气量的影响。这些影响可通过选择Activat bulking，Activate buoyancy选项以及定义相关参数来模拟。
In this basic mode, the model acts as a passive addition to the main flow model in that it does not affect the fluid flow. This is sufficient when the amount of entrained air is relatively small (<10%). If this is not the case, the flow may be affected by the air entrained in the fluid. These effects can be included by selecting the Activate bulking and Activate buoyancy options and defining the associated parameters. The Activate bulking option enables the Density evaluation model to account for the non-uniform fluid density resulting from the entrained air (see Flows with Density Variations). In this case, input the value for Density of phase #2 in the model panel.
Activate bulking选项使得Density evaluation模型解释了由掺气造成非均匀流密度的改变。在这种情况下，需要输入Density of phase #2的值。Activate buoyancy 选项使得Drift-flux模型引起了两相之间的相互作用。选中Activate bulking情况下，由于密度的不同，气泡在流体中移动影响流动。具体参见Drift Flux模型。如果选中Allow gas to escape at free surface（允许气体跃离液面 ），默许了液体质点跃离页面，回落时带入空气，详见Escape of Gas through a Free Surface。
The Activate buoyancy option enables the Drift-flux model to account for the interaction between the two phases. It requires that the Activate bulking option is already enabled. In this case, the air bubbles can move within fluid due to the difference in their densities and affect the fluid motion. See the full description of the model in Drift Flux. If the Allow gas to escape at free surface check box is selected, the entrained air can also escape back into the void, as described in Escape of Gas through a Free Surface.
Air entrainment模型模拟存储的值为Vol.fraction of entrained air（掺气量），可在后处理中导出。
The Air entrainment model evaluates and stores a quantity called Vol. fraction of entrained air, which is available for postprocessing in spatial and history plots.
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In some free-surface flows, gas may be entrained at the free surface due to turbulence or the flow conditions (e.g., an impinging jet). This has a wide variety of applications, from modeling the flow down a spillway, to bottle filling, and defect prediction in metal casting.
在FLOW-3D中，流体掺气可通过两相流模型或者使用了 Air entraiment模型的单向流来模拟。Air entrainment 通过Model Setup > Physics激活，通过平衡稳定力（重力和表面张力）和扰动力（紊动力）来预估流体中的掺气量（空泡区域）。Air entraiment 模型不仅包括了自由表面扰动产生的掺气，还包括了层流射入自由表面造成的掺气。因此，此模型在层流或者紊流中均可使用。当模拟紊流时，推荐使用k-ε双方程，RNG或者k – ω双方程模型。可通过Physics>Viscosity and Turbulence 激活，详细信息将在Turbulence（紊流）章节中讨论。
In FLOW-3D, the entrainment of gas can be modeled using the two-fluid model or, in one-fluid cases, by using the Air entrainment model. The Air entrainment model is activated on the Model Setup–>Physics tab and estimates the rate at which gas (represented by the void regions) is entrained into the flow using a balance of stabilizing forces (gravity and surface tension) and destabilizing forces (turbulence). Although the primary focus of the model is to compute the air entrainment resulting from turbulent disturbances at a free surface, the model also contains logic for handling entrainment resulting from laminar jets impinging on a free surface. Therefore, the model may be used for both laminar and turbulent cases. When modeling turbulent flows, the Two-equation , RNG or Two-equation turbulence models are recommended. These models can be activated in Physics →Viscosity and Turbulence and are discussed in more detail in Turbulence.
当使用 Air Entraiment 模型时，Entrainmet rate coefficient（含气率）必须设定为正。默认值为0.5，适合大多数情况下的初始设置。
同样可以设置流体的Surface tension coefficient（表面张力系数），包含以表面张力作为平衡力来定义掺气量的方式。这种情况下无需激活Surface tension模型。
When using the Air entrainment model, the Entrainment rate coefficient must be defined to be a positive value; the default value of 0.5 is a suitable starting point for most cases. The Surface tension coefficient for fluid can also be defined to include surface tension in the balance of forces defining the amount of entrained air. It does not activate the surface tension model.
基本模式下，掺气模型因不会影响流动，一般充当主流模型影响下的一种被动增加。当掺气量相对较小（<10%）时，显然是足够的。如果不是这种情况，则流动会受流体中掺气量的影响。这些影响可通过选择Activat bulking，Activate buoyancy选项以及定义相关参数来模拟。
In this basic mode, the model acts as a passive addition to the main flow model in that it does not affect the fluid flow. This is sufficient when the amount of entrained air is relatively small (<10%). If this is not the case, the flow may be affected by the air entrained in the fluid. These effects can be included by selecting the Activate bulking and Activate buoyancy options and defining the associated parameters. The Activate bulking option enables the Density evaluation model to account for the non-uniform fluid density resulting from the entrained air (see Flows with Density Variations). In this case, input the value for Density of phase #2 in the model panel.
Activate bulking选项使得Density evaluation模型解释了由掺气造成非均匀流密度的改变。在这种情况下，需要输入Density of phase #2的值。Activate buoyancy 选项使得Drift-flux模型引起了两相之间的相互作用。选中Activate bulking情况下，由于密度的不同，气泡在流体中移动影响流动。具体参见Drift Flux模型。如果选中Allow gas to escape at free surface（允许气体跃离液面 ），默许了液体质点跃离页面，回落时带入空气，详见Escape of Gas through a Free Surface。
The Activate buoyancy option enables the Drift-flux model to account for the interaction between the two phases. It requires that the Activate bulking option is already enabled. In this case, the air bubbles can move within fluid due to the difference in their densities and affect the fluid motion. See the full description of the model in Drift Flux. If the Allow gas to escape at free surface check box is selected, the entrained air can also escape back into the void, as described in Escape of Gas through a Free Surface.
Air entrainment模型模拟存储的值为Vol.fraction of entrained air（掺气量），可在后处理中导出。
The Air entrainment model evaluates and stores a quantity called Vol. fraction of entrained air, which is available for postprocessing in spatial and history plots.
关注flow3d公众号，每周二、五推送两篇关于flow3d软件的学习以及操作技巧，扫码关注公众号。
