Learning Forum

[Paul Stephen]

Hello ANSYS community,

I'm currently working on an external flow analysis and have encountered a perplexing issue during my simulation setup. I hope someone here can shed some light on this matter.

Problem Description:
I have created an enclosure around my body and successfully performed a Boolean (subtract) operation to create a fluid domain. This step went smoothly. Subsequently, I imported the model into ANSYS Fluent for meshing. After assigning the necessary local sizing and creating the surface mesh, I noticed some unusual messages in the console:

1) "After surface mesh, there is 1 fluid/solid region and 1 void."
2) A region named "fluid" was automatically created under the "Update Region" options, and the region type assigned was "fluid" for that region.
Attempted Solutions:
In an attempt to resolve this, I proceeded as follows:

1) I ignored the first error message and selected an option called "The region consists of only fluid with no void regions" during the setup.
2) I altered the region type for the automatically created "fluid" region from "fluid" to "dead."

However, my actions led to a new warning message in the console:

"Region fluid cannot be deleted as it is completely enclosed by other regions."

Questions:
At this point, I find myself with two primary questions:

1) Why is there a void region present when my intention was to create a fully enclosed fluid domain around my body?
2) How might the presence of this void region affect my simulation results in both cases (with and without modifications to the "fluid" region)?

I would greatly appreciate any insights, suggestions, or guidance regarding this issue. Your expertise and advice will be invaluable in helping me resolve this unexpected challenge in my external flow analysis.

Thank you in advance for your assistance.

Best regards,
Paul

[Federico Alzamora Previtali]

Hello Paul, 

can you show a screenshot of your model with the Update Region task so that we can see what should be labeled as fluid and/or dead?

Thank you

[Paul Stephen]

 

Hello 

Certainly, here’s a screenshot of my model with the Update Region task:

I've been using Boolean operations to subtract the blade portion from the domain. Surprisingly, I noticed that ANSYS automatically considers the subtracted region as fluid, even though it started as a solid geometry. This automation led me to ponder where the software recognizes a void or fluid region and why it makes this automatic assignment.

I followed the same steps as outlined in ANSYS courses, which typically result in the blade portion being subtracted without leaving a void region behind. However, it appears that ANSYS is handling this process slightly differently than I expected.

I'm reaching out to the community for insights or experiences you might have regarding this automatic assignment of fluid properties to subtracted regions in ANSYS. Your knowledge and expertise would be greatly appreciated as I continue to explore this phenomenon.

Thank you for taking the time to read my message, and I look forward to your input.

best Regards,

Paul

Best regards,

 

[Federico Alzamora Previtali]

It seems to me that you do have 1 void/dead region.

One of those regions should be left as fluid, and the second should be assigned as dead. You can display them separately to check.

[Paul Stephen]

Hello, 

The region called as geom-flow domain is the remaining portion when the blade is subtracted from the enclosure. I kept that as a fluid region and changed the other to dead. During that time I received a new warning message in the console: "Region fluid cannot be deleted as it is completely enclosed by other regions."

[Federico Alzamora Previtali]

Do you get the same warning if you choose Geometry consists of fluids and solids and/or void regions, in the Describe geometry task?

[Paul Stephen]

In the "Describe geometry" task, I noticed that there is an option that asks, "Will you cap openings and extract fluid regions?" This option has two choices: "Yes" and "No."

1. When "No" is Selected:
   If I choose "No" for this option, I have observed that the number of fluid regions is automatically adjusted to two. However, I expected to have only one fluid region. This adjustment has left me somewhat puzzled as I am not sure why it is creating two fluid regions when I explicitly select "No" for capping openings.

2. When "Yes" is Selected:
   On the other hand, when I select "Yes," an option to create a cap for the fluid region is presented. While this is a valuable feature, I must admit that I am unsure about the specific circumstances in which creating a cap for the fluid region is necessary, and where in the geometry this cap region should be created.

[Federico Alzamora Previtali]

This task is meant to be used if you import the solid-only part of a model for which the fluid was not created in the CAD. For example, you import only the solid pipe and want to create the fluid from within Fluent.

[Paul Stephen]

In my case, there should be only a fluid region and no void region. However, the software is assuming something different

[Federico Alzamora Previtali]

Shouldn't there be a void for the blade? Or do the walls of the blade reach the sides of the enclosure, meaning that the blade is not fully enclosing the blade? If the latter, then you should select Domain consists of only Fluids with no voids.

[Paul Stephen]