标题: 如何确定多孔介质系数 [打印本页] 作者: lansetian 时间: 2010-8-9 09:08 标题: 如何确定多孔介质系数 Most porous media are filters or screens for which it is impossible to determine the pressure resistance data by analysis. A perforated plate is a special case porous media where the user can create a separate analysis model of a small section of the perforated plate within a channel which only includes a few holes. The user can then run several flow rates and determine the pressure drop for each case, or run several pressure drops and determine the flow rate. The user would then enter the pressure drop vs. flow rate data into the Engineering Database for the Porous media and use the properties to represent the actual perforated plate.
We will take as an example the determination of porous medium coefficients for a perforated plate.作者: mandingo88 时间: 2010-8-9 09:10
作者: parki 时间: 2010-8-9 09:15
The next step was to run several simulations to determine the pressure drop for different velocities. In this example, the inlet velocities we chose to use are 0.1, 0.5, 2 and 5m/s.
The flow passing in each hole creates local turbulences, which then stabilize downstream.
A sample pressure variation along a curve at the center of the duct can be seen below. The pressure drops as it goes through the central hole of the plate, due to the increase in velocity caused by the restricted flow passage. Note that this phenomenon will not be present when using porous media. The pressure stabilizes downstream and this is how the pressure drop can be estimated.作者: 一点点蓝 时间: 2010-8-9 09:20
作者: pocky0610 时间: 2010-8-9 09:26
Then, comes the time to choose a method of resistance to fluid flow.
In this example, we will try to use the method named Dependency on velocity [k = (A*V+B)/r]
Coefficients A and B can be determined using these two equations for k:
k = - grad(P)/(r*V) and k = (A*V+B)/r
Equating them and simplifying r gives:
grad(P) = A*V²+B*V
In this case, grad(P) is assumed to be constant in the porous medium. Therefore, grad(P) = Pressure drop / Thickness.
The pressure drop and velocities have been determined by simulation and are shown in the table above. The thickness is the thickness of the porous medium we CHOOSE to use in the main simulation. In the case of the perforated plate, its thickness is 4mm. However, it can be decided to use a different thickness for the porous medium. Let's use 10mm for instance.作者: aljwsza 时间: 2010-8-9 09:30
可不可用汉语啊。我英语只过了三级作者: A_s 时间: 2010-8-9 09:32
我也想用中文，太翻译太难了，用金山基本可以看懂作者: ciqob 时间: 2010-8-9 09:34 作者: ljh88688609 时间: 2010-8-9 09:36
这个不属于多孔介质吧？多孔介质里面孔隙率是材料的属性。作者: qwert13145 时间: 2010-8-9 09:37
大致意思就是把多孔介质模型放到一个管道中，分别添加不同速度的边界条件做流体分析。找到在不同条件下两侧的压差。然后把这个曲线做为多孔介质的参数。
