Fluent計(jì)算熱耦合問題

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

問題:在設(shè)定邊界條件的時(shí)候,固體和液體相接觸的那個(gè)面如何設(shè)定?有人建議設(shè)為interface,但好象是用于滑移網(wǎng)格的,在計(jì)算的時(shí)候出錯(cuò)說明設(shè)為INTERFACE是錯(cuò)誤的,那么應(yīng)該怎么設(shè)定呢?

好象設(shè)置成WALL就可以了,沒有什么特別的!
在fluent里面怎么設(shè)定WALL的性質(zhì)呢?我又不知道它的實(shí)際溫度?
耦合是不需要設(shè)置的interface是兩邊網(wǎng)格不是conform時(shí)才使用,又不是真真的邊界條件,更不是你所要求的固液交界面。你既然設(shè)定完材料屬性,固體和液體,還需要設(shè)置嗎?
可以把整個(gè)管道設(shè)置為WALL的邊界條件,WALL的厚度為管道壁的厚度,管道材料的屬性如導(dǎo)熱系數(shù)等可以自己在MATERIAL里定義,計(jì)算時(shí)只要知道傳送介質(zhì)的溫度和管道外界的溫度等邊界條件,在管道WALL的邊界條件選COUPLE,就可以耦合管道內(nèi)外溫度進(jìn)行求解,最近正在采用這種辦法進(jìn)行計(jì)算。
我是用phoenics軟件的,但是最近也是需要解決一些耦合的問題,我想請教一個(gè)問題:
管道WALL的邊界條件選COUPLE是不是因?yàn)樗倪吔缂扔袀魉徒橘|(zhì)的溫度邊界,也有管道外界的溫度邊界的原因??
我認(rèn)為如果上面的問題你的回答是肯定的話,你的這種做法根本行不通,主要原因在于傳送介質(zhì)的溫度你根本沒辦法知道的,這就是耦合問題跟別的不同的地方所在!我用的是fluent,個(gè)人認(rèn)為,其中的couple求解可能就是因?yàn)榱鲃?dòng)方向的溫度分布事先并不知道,比如求解管壁內(nèi)外的對流和管壁的導(dǎo)熱傳熱,這時(shí)可能就要用到couple了,這種求解估計(jì)就是根據(jù)定義的邊界條件,逐步迭代求解流動(dòng)方向上各節(jié)點(diǎn)的溫度分布的
不過fluent中的用couple的邊界條件求解感覺有點(diǎn)太傻瓜化了,自己驗(yàn)證了好多case,結(jié)果總是不能令人完全信服,搞的問題太復(fù)雜了?？纯刺战淌诘臄?shù)值傳熱學(xué)后面一章的流固耦合問題
另外,如果你把"整個(gè)管道設(shè)置為WALL的邊界條件"
你怎么在這個(gè)固體WALL來MAPPING MESH,又怎么可以算出這個(gè)固體WALL里面的溫度梯度呢?
一點(diǎn)必須注意的就是:你的計(jì)算NODES只是在計(jì)算區(qū)域,不是在WALL.
耦合計(jì)算就是不需要設(shè)置,建體的時(shí)候用split將流體域和固體域分開,兩者共面,分別設(shè)定成fluid和solid后,自動(dòng)將兩者的交界面定義成coupled邊界條件,不需要再指定。wall可以指定厚度,一般我都是安實(shí)際尺寸畫出網(wǎng)格作為計(jì)算域一部分進(jìn)行計(jì)算。好像就是這樣,沒有他說得那么復(fù)雜。這種壁面可以不用設(shè)置的。網(wǎng)格當(dāng)然在gambit里面建了,邊界條件給定和計(jì)算當(dāng)然在Fluent里面進(jìn)行了。
其實(shí)關(guān)于TWO SIDE WALL的熱邊界條件設(shè)定問題,FLUENT里的UG寫得很清楚,的確不需要再設(shè)置其他條件,WALL的厚度也是可以設(shè)置的,以下是FLUENT的UG里的描述:

Thermal Conditions for Two-Sided Walls
If the wall zone has a fluid or solid region on each side, it is called a``two-sided wall''. When you read a grid with this type of wall zone intoFLUENT, a ``shadow'' zone will automatically be created so that each side ofthe wall is a distinct wall zone. In the Wall panel, the shadow zone's namewill be shown in the Shadow Face Zone field. You can choose to specifydifferent thermal conditions on each zone, or to couple the two zones:
To couple the two sides of the wall, select the Coupled option under ThermalConditions. (This option will appear in the Wall panel only when the wall is atwo-sided wall.) No additional thermal boundary conditions are required,because the solver will calculate heat transfer directly from the solution inthe adjacent cells. You can, however, specify the material type, wallthickness, and heat generation rate for thin-wall thermal resistancecalculations, as described above. Note that the resistance parameters you setfor one side of the wall will automatically be assigned to its shadow wallzone. Specifying the heat generation rate inside the wall is useful if, forexample, you are modeling printed circuit boards where you know the electricalpower dissipated in the circuits but not the heat flux or walltemperature.
To uncouple the two sides of the wall and specify different thermal conditionson each one, choose Temperature or Heat Flux as the thermal condition type. (Convection and Radiation are not applicable for two-sided walls.) Therelationship between the wall and its shadow will be retained, so that you cancouple them again at a later time, if desired. You will need to set therelevant parameters for the selected thermal condition, as described above. Thetwo uncoupled walls can have different thicknesses, and are effectivelyinsulated from one another. If you specify a non-zero wall thickness for theuncoupled walls, the thermal boundary conditions you set will be specified on theouter sides of the two thin walls, as shown in Figure 6.13.3,where is the Temperature (or is the Heat Flux) specified on one wall and is theTemperature (or is the Heat Flux) specified on the other wall. and are thethermal conductivities of the uncoupled thin walls. Note that the gap betweenthe walls in Figure 6.13.3 is not part of the model; it is included in thefigure only to show where the thermal boundary condition for each uncoupledwall is applied.
雖然如此,但是FLUENT在處理流固耦合問題時(shí),的確很弱,如果只關(guān)心流體的問題,可以用FLUENT算,如果流體和固體問題都很重要。個(gè)人覺得還是用ANSYS計(jì)算比較可行,個(gè)人觀點(diǎn)。
至于INTERFACE邊界條件,在FLUENT里只有采用滑移網(wǎng)格才能使用。

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