fluent unit計(jì)算單位和設(shè)計(jì)單位、網(wǎng)格單位、縮放單位的關(guān)系

2016-09-20 by:CAE仿真在線來源:互聯(lián)網(wǎng)

fluent 里頭有幾個(gè)單位概念unit,如:計(jì)算單位和設(shè)計(jì)單位、網(wǎng)格單位、縮放單位的關(guān)系

1、Define Units 通過菜單 define-》units設(shè)置,這里面的值是計(jì)算的單位,這個(gè)單位必須與網(wǎng)格尺寸的單位、udf代碼、參數(shù)輸入中的所有數(shù)值的單位保持一致

2、設(shè)計(jì)單位:即設(shè)計(jì)CAD模型時(shí)候使用的單位,這個(gè)單位極為原始模型單位,后面fluent中必須與之保持實(shí)質(zhì)長(zhǎng)度上的一致即可,比如創(chuàng)建的時(shí)候時(shí)1cm,則對(duì)應(yīng)于fluent默認(rèn)的1e-2m

3、網(wǎng)格單位:其實(shí)就是設(shè)計(jì)單位,因?yàn)閯澐志W(wǎng)格時(shí)候使用的單位同樣基于CAD實(shí)際模型的尺寸。但是這個(gè)要與網(wǎng)格放縮單位相互區(qū)別。

4、fluent網(wǎng)格單位放縮

這是個(gè)容易混淆的概念,很多人認(rèn)為這就是fluent的單位,其實(shí)不是。

我們可以參考下面的fluent的幫助文件來進(jìn)行原汁原味的說明:

#5.8.14. Scaling the Mesh

Internally, ANSYS Fluent stores the computational mesh in meters, the SI unit of length. When mesh information is read, it is assumed that the mesh was generated in units of meters. If your mesh was created using a different unit of length (inches, feet, centimeters, and so on), you must scale the mesh to meters. To do this, you can select from a list of common units to convert the mesh or you can supply your own custom scale factors. Each node coordinate will be multiplied by the corresponding scale factor.

Scaling can also be used to change the physical size of the mesh. For instance, you could stretch the mesh in the direction by assigning a scale factor of 2 in the direction and 1 in the and directions. This would double the extent of the mesh in the direction. However, you should use anisotropic scaling with caution, since it will change the aspect ratios of the cells in your mesh.

翻譯為:fluent內(nèi)部使用的是SI國(guó)際單位,即m,kg,s,N,這個(gè)在讀取網(wǎng)格mesh數(shù)據(jù)時(shí)是默認(rèn)的,即一個(gè)單位就是1m

下面是解釋:

為啥fluent提供一個(gè)Scaling the Mesh這樣一個(gè)明顯的功能呢?

答案是:有些軟件輸出的mesh并沒有轉(zhuǎn)換成meter,比如mm,那么1mm在fluent中會(huì)認(rèn)為是1m,這個(gè)時(shí)候請(qǐng)你打開這個(gè)窗口,看看xmin,ymin,xmax,ymax這四個(gè)模型規(guī)模,是否是對(duì)的,如果對(duì)的,則不需要去處理了,如果是不對(duì)的,那么就要執(zhí)行scale

這個(gè)地方會(huì)影響fluent對(duì)模型尺寸的理解,一定要注意。

但是如果在icem,gambit或fluent meshing,ansys workbench mesh中直接輸入到fluent的基本不用做處理,因?yàn)樗麄兌紩?huì)在劃分網(wǎng)格的時(shí)候,完全遵守cad的原始尺寸轉(zhuǎn)換成SI單位了。

但是其他軟件這一點(diǎn)卻不能保證,所以還是要注意。

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