fluent:[讨论]对inlet/outlet vent边界的理解

2017-03-21 by:CAE仿真在线来源:互联网

其实大部分的进出口边界条件都好理解,最让人困惑的是Pressure inlet/outlet和 inlet/outlet vent的区别。下面是我对inlet/outlet vent边界的理解:

Pressure inlet/outlet是界面上没有遮挡的进出口边界,需要定义进出口边界周围环境的压力。

而inlet/outlet vent是界面上被均匀遮挡的进出口边界,如下图所示,除了需要定义边界周边环境的压力外,还需要定义压力损失系数。

我这样理解的根据是帮助文件里面介绍压力损失系数的一段话:参看下图

其中第一句提到“inlet vent被认为是无限薄的(狭窄的),通过该边界的压降与动态压力水头成比例,该比例是用户根据经验提供的损失系数。”既然是“无限薄的(狭窄的)”的进出口边界,就很容易让人联想到百叶窗类型的通风口,气流通过这样的通风口时的确会产生压降。

当然,我不确定这样的理解就是正确的。还请有经验的网友指正。

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以下是帮助文件理对进出口边界的概述的翻译。贴出来免得将来又得看英文原文。

FLUENT中的进出口边界选项如下:

1.Velocity inlet速度进口边界:用来定义进口的速度和其他参数

2.Pressure inlet压力进口边界:用来定义进口的总压和其他参数

3.Mass flow inlet质量进口边界:用于定义可压缩流的进口质量流量,没有必要在不可压缩流动中使用质量流量入口边界,因为当密度不变时,确定了流体速度即可确定质量流量。像速度进口和压力进口一样,质量进口也需要定义一些其他的参数。

4.Pressure outlet压力出口边界:用于定义出口的静压(和其他考虑到回流的参数),当迭代过程中出口存在回流时,采用压力出口边界可以取得更好的收敛性。

5.Pressure far-field压力远场边界:用于定义一个无限远处的可压缩自由流(free-stream flow),这个边界需要定义自由流马赫数(free-stream Mach number)和其他静态参数。这个边界只可用于可压缩流。

6.Outflow边界:用于出口速度和压力事先不清楚的出口边界,适用于出口流动接近于完全发展流动(fully developed flow),因为outflow边界假设边界处沿流动方向的各种物理量梯度为0(压力梯度除外)。这种边界不适用于可压缩流的计算。

注意以下情况不可使用outflow边界:

a.当入口为Pressure inlet时,出口应选用Pressure outlet

b.当计算可压缩流动时

c.当计算密度可变的非稳态流动时,即使采用的是不可压缩流模型也不能用outflow边界

d.多相流模型不可用outflow边界,唯一例外是明渠模型(open chennel)

7.Inlet vent边界:用于定义入口的损失系数、入口周围环境的总压和温度.

8.Intake fan进气风扇边界:用于定义一个外部进气风扇,其压力突变量(pressure jump)、流动方向、周围环境总压和温度需要被定义。

9.Outlet vent边界:用于定义出口的损失系数、入口周围环境的总压和温度.

10.Exhaust fan边界:用于定义一个外部排气风扇,其压力突变量(pressure jump)、流动方向、周围环境总压和温度需要被定义。

The inlet and exit boundary condition options in ANSYS FLUENT are as follows:

1.Velocity inlet boundary conditions are used to define the velocity and scalar properties of the flow at inlet boundaries.

2.Pressure inlet boundary conditions are used to define the total pressure and other scalar quantities at flow inlets.

3.Mass flow inlet boundary conditions are used in compressible flows to prescribe a mass flow rate at an inlet. It is not necessary to use mass flow inlets in incompressible flows because when density is constant, velocity inlet boundary conditions will fix the mass flow. Like pressure and velocity inlets, other inlet scalars are also prescribed.

4.Pressure outlet boundary conditions are used to define the static pressure at flow outlets (and also other scalar variables, in case of backflow). The use of a pressure outlet boundary condition instead of an outflow condition often results in a better rate of convergence when backflow occurs during iteration.

5.Pressure far-field boundary conditions are used to model a free-stream compressible flow at infinity, with free-stream Mach number and static conditions specified. This boundary type is available only for compressible flows.

6.Outflow boundary conditions are used to model flow exits where the details of the flow velocity and pressure are not known prior to solution of the flow problem. They are appropriate where the exit flow is close to a fully developed condition, as the outflow boundary condition assumes a zero streamwise gradient for all flow variables except pressure. They are not appropriate for compressible flow calculations.

7.Inlet vent boundary conditions are used to model an inlet vent with a specified loss coefficient, flow direction, and ambient (inlet) total pressure and temperature.

8.Intake fan boundary conditions are used to model an external intake fan with a specified pressure jump, flow direction, and ambient (intake) total pressure and temperature.

9.Outlet vent boundary conditions are used to model an outlet vent with a specified loss coefficient and ambient (discharge) static pressure and temperature.

10.Exhaust fan boundary conditions are used to model an external exhaust fan with a specified pressure jump and ambient (discharge) static pressure.

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