💥💥💥 How to handle with complex geometries (models) in Ansys Fluent?

ANSYS Fluent is a powerful software for simulating fluid dynamics and heat transfer problems. It can handle complex geometries (models) by using different meshing methods and workflows. Meshing is the process of dividing the geometry into small elements that can be used for numerical calculations. Depending on the type and quality of the geometry, you may need to use different meshing tools and techniques.

One of the meshing methods available in ANSYS Fluent is the Watertight Geometry Workflow. This workflow is suitable for clean and watertight geometries, which means that there are no gaps, overlaps, or errors in the geometry. The Watertight Geometry Workflow can automatically generate a high-quality mesh for complex geometries, such as aircraft, cars, or turbines. You can also customize the mesh settings and refine the mesh in specific regions. To learn more about the Watertight Geometry Workflow, you can watch this video or take this course.

Another meshing method available in ANSYS Fluent is the Fault-Tolerant Workflow. This workflow is suitable for dirty and non-watertight geometries, which means that there are some defects or errors in the geometry. The Fault-Tolerant Workflow can wrap the geometry with a thin layer of mesh and create a fluid region without modifying the original geometry. This can save a lot of time and effort in geometry preparation and meshing. To learn more about the Fault-Tolerant Workflow, you can watch this webinar or this video.

What is Watertight Geometry Workflow?

The Watertight Geometry Workflow is a meshing method in ANSYS Fluent that can automatically generate a high-quality mesh for complex geometries, such as aircraft, cars, or turbines. The workflow guides users through a step-by-step process of simple, intuitive inputs, while behind the scenes, Fluent Meshing uses built-in intelligence and automation to create a CFD mesh using its sophisticated meshing technology. The workflow can also be customized and saved for future use. The Watertight Geometry Workflow is suitable for clean and watertight geometries, which means that there are no gaps, overlaps, or errors in the geometry. You can learn more about the Watertight Geometry Workflow by taking this course or watching this video. 😊

How do I know if my geometry is watertight?

To check if your geometry is watertight, you can use the Check Geometry tool in SpaceClaim or Fluent Meshing. This tool will detect any errors or defects in your geometry, such as gaps, overlaps, or non-manifold edges, that can prevent the geometry from being watertight. A watertight geometry is one that has no holes or leaks, and can be completely filled with fluid. You can access the Check Geometry tool by selecting the geometry in the structure tree, right-clicking, and choosing Check Geometry¹. Alternatively, you can also use the Fault Detection tool in DesignModeler¹. You can learn more about how to check and repair your geometry by watching this video or taking this course. 😊

Can you recommend any other tools for geometry preparation?

Sure, there are some other tools that you can use for geometry preparation in ANSYS Fluent. Here are some of them:

• ANSYS DesignModeler: This is a CAD tool that is integrated with ANSYS Workbench and can be used to create, modify, and repair geometries for CFD analysis. You can use parametric modeling, sketching, Boolean operations, and other features to create complex geometries. You can also use the Fault Detection tool to identify and fix any errors or defects in your geometry. You can learn more about ANSYS DesignModeler by taking this course or watching this video.
• ANSYS Meshing: This is a meshing tool that is integrated with ANSYS Workbench and can be used to generate high-quality meshes for CFD analysis. You can use different meshing methods, such as patch conforming, patch independent, cutcell, and polyhedral, to create structured, unstructured, or hybrid meshes. You can also use local sizing controls, inflation layers, and mesh quality checks to optimize your mesh. You can learn more about ANSYS Meshing by taking this course or watching this video.
• ANSYS Fluent Meshing: This is a meshing tool that is integrated with ANSYS Fluent and can be used to generate high-quality meshes for CFD analysis. You can use different meshing workflows, such as Watertight Geometry Workflow, Fault-Tolerant Workflow, and Mosaic Meshing, to create surface and volume meshes for complex geometries. You can also use mesh adaption, mesh morphing, and mesh quality checks to improve your mesh. You can learn more about ANSYS Fluent Meshing by taking this course or watching this video.

What is the difference between ANSYS Meshing and Fluent Meshing?

ANSYS Meshing and Fluent Meshing are two different meshing tools that can be used for CFD analysis. They have some common features, such as generating 3D meshes with tet, hex, prism/wedge, and pyramid elements, and integrating with ANSYS Workbench. However, they also have some differences, such as:

• Fluent Meshing is a strictly 3D mesher, while ANSYS Meshing can generate 2D and 3D meshes.
• Fluent Meshing can generate meshes with conformal polyhedron elements, which can reduce cell count and improve gradient calculations, while ANSYS Meshing cannot.
• Fluent Meshing has different meshing workflows, such as Watertight Geometry Workflow, Fault-Tolerant Workflow, and Mosaic Meshing, which can handle complex geometries with different levels of quality and automation, while ANSYS Meshing has physics-aware mesh settings that can be customized for different analysis types.
• Fluent Meshing can handle non-conformal meshes at interfaces, which means that the mesh nodes do not have to match between adjacent cells, while ANSYS Meshing requires conformal meshes.
• Fluent Meshing is more suitable for experienced users who want to have more control and flexibility over the meshing process, while ANSYS Meshing is more suitable for beginners or intermediate users who want to have a simpler and faster meshing process.

What is polyhedral meshing?

Polyhedral meshing is a method of generating meshes for computational fluid dynamics (CFD) analysis, where each cell is a polyhedron with multiple faces. Polyhedral meshes can have several advantages over other types of meshes, such as:

• They can reduce the number of cells and memory requirements, while maintaining the same accuracy and resolution.
• They can better capture the gradients and flow alignments, because of the multiple neighbors and directions of each cell.
• They can improve the convergence and stability of the numerical solver, because of the more off-diagonal terms in the linear system.

Polyhedral meshes can be created from different sources, such as tetrahedral meshes, octree meshes, or surface meshes. There are different tools and workflows that can generate polyhedral meshes, such as ANSYS Fluent Meshing, Simcenter STAR-CCM+, or Polygon Mesh Processing. 

How do I create a polyhedral mesh in ANSYS Fluent?

To create a polyhedral mesh in ANSYS Fluent, you can use one of the following methods:

• Converting the entire domain into polyhedral cells. This method is applicable only for meshes that contain tetrahedral and/or wedge/prism cells. To do this, you can use the Mesh/Polyhedra/Convert Domain menu in Fluent. Fluent will automatically decompose each non-hexahedral cell into multiple sub-volumes called “duals” and then agglomerate them into polyhedral cells around the original nodes. You can learn more about this method by reading the ANSYS Fluent User’s Guide¹ or watching this video².
• Converting skewed tetrahedral cells to polyhedral cells. This method is applicable for meshes that contain some tetrahedral cells that have poor quality or skewness. To do this, you can use the Mesh/Polyhedra/Convert Skewed Cells menu in Fluent. Fluent will identify the skewed cells and convert them to polyhedral cells using the same dual decomposition and agglomeration technique as the previous method. You can learn more about this method by reading the ANSYS Fluent User’s Guide¹.
• Using the Watertight Geometry Workflow. This method is suitable for clean and watertight geometries, which means that there are no gaps, overlaps, or errors in the geometry. To do this, you can use the Fluent Meshing mode in Workbench and select the Watertight Geometry Workflow option. Fluent Meshing will guide you through a step-by-step process of simple, intuitive inputs, while behind the scenes, it will use built-in intelligence and automation to create a polyhedral mesh using its sophisticated meshing technology. You can learn more about this method by taking this course³ or watching this video⁴.

What is the difference between polyhedral and tetrahedral meshes?

Polyhedral and tetrahedral meshes are two types of meshes that can be used for computational fluid dynamics (CFD) analysis. They have some similarities and differences, such as:

• Polyhedral meshes are derived from tetrahedral meshes by forming polygons around each node in the tetrahedral mesh¹.
• Polyhedral meshes can reduce the number of cells and memory requirements, while maintaining the same accuracy and resolution as tetrahedral meshes¹².
• Polyhedral meshes can better capture the gradients and flow alignments, because of the multiple neighbors and directions of each cell¹².
• Polyhedral meshes can improve the convergence and stability of the numerical solver, because of the more off-diagonal terms in the linear system¹².
• Tetrahedral meshes are more general and can handle any geometry, while polyhedral meshes require clean and watertight geometries²³.
• Tetrahedral meshes are easier and faster to generate, while polyhedral meshes require more processing and time²⁴.

How do I choose the best meshing method for my project?

Choosing the best meshing method for your project depends on several factors, such as:

• The geometry and complexity of your model. Some geometries may require more refinement or special treatment to capture the flow features and boundary conditions accurately.
• The physics and solver settings of your simulation. Some physics models, such as turbulence, heat transfer, or multiphase, may require finer or different types of meshes to ensure numerical stability and convergence.
• The computational resources and time available for your simulation. Finer meshes usually result in more accurate solutions, but they also increase the computational cost and time of the simulation.

There is no single meshing method that works best for all cases, so you may need to try different methods and compare the results. However, some general guidelines that can help you choose a suitable meshing method are:

• Use adaptive meshing or physics-controlled meshing to automatically adjust the mesh density according to the solution gradient and the physics settings¹².
• Use boundary layer meshing or inflation layers to resolve the thin regions near the walls where the flow velocity changes rapidly³⁴.
• Use polyhedral meshing or mosaic meshing to reduce the number of cells and improve the solution quality and convergence, especially for complex geometries⁴⁵.
• Use structured or hexahedral meshing for simple geometries or regions where the flow is aligned with the mesh, as they can reduce the numerical errors and diffusion²⁵.
• Use unstructured or tetrahedral meshing for complex geometries or regions where the flow is not aligned with the mesh, as they can conform to any shape and capture the flow features²⁵.