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

 

[Sunil Lilhare]

 

Hello, which tool are you using for meshing? Please make sure that your CAD is free from any errors before meshing. If you are using Watertight Workflow Meshing then assuming that you have only one fluid domain, the geometry consists of only one fluid region and no voids is the valid option in the Describe Geometry task.

Similarly, you will have one fluid region in the update regions task which is basically the fluid domain surrounding substracted portion of the CAD. If you are not including more than one fluid region.

To know more about the Describe Geometry and Update Regions task of Ansys Fluent Meshing Watertight Geometry Workflow, please refer to the link of a course given below

Describe Geometry - ANSYS Innovation Courses

 

[Paul Stephen]

 

I’m currently working on a project involving CAD geometry imported into the Space Claim, and creating the domains. Here’s what I’ve observed:

 

1. Creating a Domain: In Space Claim, I import a CAD geometry and create a domain around it.

2. Creating a Second Domain Inside: I then create another domain inside the initial one using Space Claim’s capabilities.

3. Specifying it as a BOI: Afterward, I specify this inner domain as a “BOI” (Bodies of Influence) when performing Fluent (watertight) meshing.

 

Now, here’s the intriguing part:

 

• When I don’t create an extra domain inside and simply subtract the geometry, I receive a message stating, “The region consists of 1 fluid and no voids.”

• However, when I create an inner domain (BOI) and proceed with the meshing process, it displays a different message: “The region consists of 1 fluid and 1 void.”

 

I’m currently following the course provided by ANSYS, and it’s perplexing to me why I’m consistently getting this void region when I use the BOI approach.