fluent:[討論]對inlet/outlet vent邊界的理解

2017-03-21 by:CAE仿真在線來源:互聯(lián)網(wǎng)

其實大部分的進出口邊界條件都好理解,最讓人困惑的是Pressure inlet/outlet和 inlet/outlet vent的區(qū)別。下面是我對inlet/outlet vent邊界的理解:

Pressure inlet/outlet是界面上沒有遮擋的進出口邊界,需要定義進出口邊界周圍環(huán)境的壓力。

而inlet/outlet vent是界面上被均勻遮擋的進出口邊界,如下圖所示,除了需要定義邊界周邊環(huán)境的壓力外,還需要定義壓力損失系數(shù)。

我這樣理解的根據(jù)是幫助文件里面介紹壓力損失系數(shù)的一段話:參看下圖

其中第一句提到“inlet vent被認為是無限薄的(狹窄的),通過該邊界的壓降與動態(tài)壓力水頭成比例,該比例是用戶根據(jù)經(jīng)驗提供的損失系數(shù)。”既然是“無限薄的(狹窄的)”的進出口邊界,就很容易讓人聯(lián)想到百葉窗類型的通風口,氣流通過這樣的通風口時的確會產(chǎn)生壓降。

當然,我不確定這樣的理解就是正確的。還請有經(jīng)驗的網(wǎng)友指正。

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以下是幫助文件理對進出口邊界的概述的翻譯。貼出來免得將來又得看英文原文。

FLUENT中的進出口邊界選項如下:

1.Velocity inlet速度進口邊界:用來定義進口的速度和其他參數(shù)

2.Pressure inlet壓力進口邊界:用來定義進口的總壓和其他參數(shù)

3.Mass flow inlet質量進口邊界:用于定義可壓縮流的進口質量流量,沒有必要在不可壓縮流動中使用質量流量入口邊界,因為當密度不變時,確定了流體速度即可確定質量流量。像速度進口和壓力進口一樣,質量進口也需要定義一些其他的參數(shù)。

4.Pressure outlet壓力出口邊界:用于定義出口的靜壓(和其他考慮到回流的參數(shù)),當?shù)^程中出口存在回流時,采用壓力出口邊界可以取得更好的收斂性。

5.Pressure far-field壓力遠場邊界:用于定義一個無限遠處的可壓縮自由流(free-stream flow),這個邊界需要定義自由流馬赫數(shù)(free-stream Mach number)和其他靜態(tài)參數(shù)。這個邊界只可用于可壓縮流。

6.Outflow邊界:用于出口速度和壓力事先不清楚的出口邊界,適用于出口流動接近于完全發(fā)展流動(fully developed flow),因為outflow邊界假設邊界處沿流動方向的各種物理量梯度為0(壓力梯度除外)。這種邊界不適用于可壓縮流的計算。

注意以下情況不可使用outflow邊界:

a.當入口為Pressure inlet時,出口應選用Pressure outlet

b.當計算可壓縮流動時

c.當計算密度可變的非穩(wěn)態(tài)流動時,即使采用的是不可壓縮流模型也不能用outflow邊界

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

7.Inlet vent邊界:用于定義入口的損失系數(shù)、入口周圍環(huán)境的總壓和溫度.

8.Intake fan進氣風扇邊界:用于定義一個外部進氣風扇,其壓力突變量(pressure jump)、流動方向、周圍環(huán)境總壓和溫度需要被定義。

9.Outlet vent邊界:用于定義出口的損失系數(shù)、入口周圍環(huán)境的總壓和溫度.

10.Exhaust fan邊界:用于定義一個外部排氣風扇,其壓力突變量(pressure jump)、流動方向、周圍環(huán)境總壓和溫度需要被定義。

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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