# How to calculate free-surface area in a computational cell

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 December 21, 2017, 05:49 How to calculate free-surface area in a computational cell #1 New Member   Join Date: Aug 2017 Posts: 20 Rep Power: 5 hi experts, I am working on a two-phase (gas-liquid) flow problem using the VOF method. I need to calculate the surface area of the free-surface in a computational cell. I am wondering if there is any macro for this purpose. If not, how can I calculate this surface area?

 December 22, 2017, 04:25 #2 New Member   Doruk Yelkenci Join Date: Apr 2017 Posts: 20 Rep Power: 5 I am currently working on a similar case. I am trying to find the surface normal. They way I see it is very difficult to get it by using ansys fluent. There are no macros except C_VOF which only gives you the volume fraction of the cell. Even tough ansys fluent calculates these values we need (area, normal, curvature of the area etc) they dont let us use them in udf. You have to calculate them again in your own way then use them. I suggest you to find some papers about how to calculate these values.

 December 22, 2017, 13:10 Calculate the interfacial area density using C_VOF_G #3 Member   Daniel Edebro Join Date: Feb 2016 Location: Gothenburg Posts: 39 Rep Power: 6 You can calculate the interfacial area density by first calculating the gradient of VOF. The macro is called "C_VOF_G" The surface area is calculated by taking the absolute value of the components of this.

 December 22, 2017, 15:38 #4 New Member   Join Date: Aug 2017 Posts: 20 Rep Power: 5 Thanks for your replies. As far as I know, the macro "C_VOF_G"[x] returns the gradients of the VOF function in different directions. A normal to the free-surface can be found by the magnitude of the VOF function. My problem is how to calculate the free-surface area in a computational cell.

 December 22, 2017, 16:21 #5 Member   Daniel Edebro Join Date: Feb 2016 Location: Gothenburg Posts: 39 Rep Power: 6 Check out this thread How to get the surface area between two phases in VOF model

March 12, 2018, 02:05
#6
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xiatiantian
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Quote:
 Originally Posted by DEd You can calculate the interfacial area density by first calculating the gradient of VOF. The macro is called "C_VOF_G" The surface area is calculated by taking the absolute value of the components of this.
Hi DEd,
Could you tell me how to use the macro "C_VOF_G"? When I load the macro by UDF, it always has the error:
received a fatal signal (Segmentation fault)

July 12, 2018, 13:24
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 Originally Posted by xiatt Hi DEd, Could you tell me how to use the macro "C_VOF_G"? When I load the macro by UDF, it always has the error: received a fatal signal (Segmentation fault)
Dear Xiatt,

You should prevent the solver from freeing up memory. You can do that by answering "yes" to “Keep temporary solver memory from being freed?” from /solve/set/expert.

I hope it helps.