💥💥💥 How to define good mesh in Ansys Fluent?

 A good mesh in Ansys Fluent is one that has low skewness, aspect ratio, and size change values for the cells. These parameters measure the quality and uniformity of the mesh, and affect the accuracy and convergence of the solution. According to the Ansys Knowledge Forum¹, the recommended limits for these parameters are:

• Skewness: less than 0.9 (good 0-0.9, average 0.9-0.95, poor > 0.95)
• Aspect ratio: less than 10 in the domain and less than 100 in the boundary layers
• Size change: less than 10

You can check these values using the Mesh Quality tool in Fluent Meshing, or by displaying and inspecting the geometry. You can also use the Surface Mesh Improvement tool to adjust the face quality limit and the collapse skewness limit to improve the surface mesh quality.

If you want to learn more about how to generate and improve a mesh in Ansys Fluent, you can watch some of the video tutorials from the search results, such as How to Improve Surface Mesh Quality in Ansys Fluent Meshing’s Watertight Geometry Workflow or ANSYS Fluent: Complete Meshing-to-Postprocessing Workflow.

How to improve mesh quality in Ansys Fluent?

Mesh quality is an important factor in Ansys Fluent, as it affects the accuracy and convergence of the solution. There are several ways to improve the mesh quality, depending on the type and shape of the mesh. Here are some general tips and resources that might help you:

• Check the mesh quality parameters, such as skewness, aspect ratio, and size change, using the Mesh Quality tool in Fluent Meshing. These parameters measure the quality and uniformity of the mesh, and have recommended limits for a good mesh¹.
• Use the Surface Mesh Improvement tool to adjust the face quality limit and the collapse skewness limit to improve the surface mesh quality. The face quality limit is the skewness threshold for improving the faces, and the collapse skewness limit is the skewness threshold for collapsing the faces. You can find more details about these options in this forum post².
• Use different meshing methods, such as sweep, polyhedral, or hexahedral, depending on your geometry and flow physics. You can also use body sizing or sphere of influence to control the element size in specific regions. You can learn more about these methods in this video tutorial³ or this user guide⁴.
• Use smoothing and diagonal swapping to improve the cell shape and alignment. Smoothing adjusts the node positions to reduce cell distortion, and diagonal swapping changes the cell connectivity to reduce cell skewness. You can find more information about these options in this user guide⁴.
• Modify the geometry to avoid sharp angles, small gaps, or thin surfaces that might cause meshing difficulties. You can use tools such as scale, translate, merge, separate, or fuse to modify the geometry in Fluent Meshing. You can also use CAD tools to create a clean and watertight geometry before importing it to Fluent Meshing. You can watch this video tutorial⁵ to see an example of a complete meshing-to-postprocessing workflow.

How do I know if my mesh is good enough for my simulation?

There is no definitive answer to whether your mesh is good enough for your simulation, as it depends on the complexity of your geometry, the physics of your problem, and the accuracy and convergence criteria you have set. However, there are some general guidelines and methods that you can use to evaluate and improve your mesh quality, such as:

• Check the mesh quality parameters, such as skewness, aspect ratio, and size change, using the Mesh Quality tool in Fluent Meshing. These parameters measure the quality and uniformity of the mesh, and have recommended limits for a good mesh.
• Compare the results of your simulation with different mesh sizes and types, and see if they converge to a similar solution. You can use the Solution History tool in Fluent to monitor and plot the residuals, forces, moments, or other quantities of interest during the simulation. You can also use the Solution Adaption tool to refine or coarsen the mesh based on gradients, errors, or regions of interest.
• Validate your results with experimental data or analytical solutions, if available. You can use the Validation tool in Fluent to compare your results with data from various sources, such as NACA airfoils, NASA rotor 37, or Ahmed body. You can also use the Report Definitions tool to calculate and display various quantities of interest, such as lift coefficient, drag coefficient, or pressure drop.

How do I use Solution Adaption to refine my mesh?

Solution Adaption is a tool in Ansys Fluent that allows you to refine or coarsen your mesh based on the solution data, such as gradients, errors, or regions of interest. You can use Solution Adaption to improve the accuracy and convergence of your simulation, as well as reduce the cell count and computational time. To use Solution Adaption, you need to follow these steps:

• Define the adaption criteria, such as boundary, gradient, isovalue, region, volume, or yplus/ystar. You can also create custom adaption fields using expressions or user-defined functions. You can find more details about the adaption criteria in this user guide.
• Mark the cells that meet the adaption criteria using the Mark button. You can also preview the marked cells using the Display button. You can modify the adaption criteria and mark the cells again until you are satisfied with the result.
• Adapt the mesh using the Adapt button. This will create a new mesh with refined or coarsened cells based on the adaption criteria. You can also undo the adaption using the Undo button.
• Check the mesh quality using the Mesh Quality tool in Fluent Meshing. You can also display and inspect the geometry to see the changes in the mesh. You can use the Surface Mesh Improvement tool to adjust the face quality limit and the collapse skewness limit to improve the surface mesh quality.
• Initialize and continue the solution using the new mesh. You can monitor and plot the residuals, forces, moments, or other quantities of interest using the Solution History tool in Fluent. You can also compare your results with experimental data or analytical solutions using the Validation tool or the Report Definitions tool in Fluent.

You can repeat these steps until you achieve a satisfactory solution with a good mesh quality. You can also use Solution Adaption in combination with other meshing methods, such as sweep, polyhedral, or hexahedral, depending on your geometry and flow physics. 

How does mesh quality affect the adaption criteria?

Mesh quality is an important factor that affects the adaption criteria in Ansys Fluent, as it determines the accuracy and convergence of the solution. The adaption criteria are the parameters that define which cells need to be refined or coarsened based on the solution data, such as gradients, errors, or regions of interest. The mesh quality parameters, such as skewness, aspect ratio, and size change, measure the quality and uniformity of the mesh, and have recommended limits for a good mesh¹.

The mesh quality affects the adaption criteria in two ways:

• First, the mesh quality influences the solution data that are used to define the adaption criteria. For example, if the mesh is too coarse or distorted, the gradients or errors of the solution variables might be inaccurate or noisy, which can lead to incorrect or inefficient adaption. Therefore, it is recommended to check and improve the mesh quality before performing adaption.
• Second, the mesh quality changes after the adaption process, as new cells are created or removed based on the adaption criteria. For example, if the adaption criteria are too strict or too loose, the mesh might become too fine or too coarse, which can affect the cell shape and alignment. Therefore, it is recommended to check and improve the mesh quality after performing adaption.

There are several ways to check and improve the mesh quality in Ansys Fluent, such as using the Mesh Quality tool in Fluent Meshing, using the Surface Mesh Improvement tool to adjust the face quality limit and the collapse skewness limit, using smoothing and diagonal swapping to improve the cell shape and alignment, or modifying the geometry to avoid sharp angles, small gaps, or thin surfaces. 

How does adaption affect the cell count and computational time?

Adaption is a method of refining or coarsening the mesh based on the solution data, such as gradients, errors, or regions of interest. Adaption can affect the cell count and computational time in Ansys Fluent in the following ways:

• Adaption can reduce the cell count by coarsening the mesh in areas where the solution is smooth or less important, and increase the cell count by refining the mesh in areas where the solution is complex or critical. This can improve the accuracy and efficiency of the simulation, as well as reduce the memory and disk space requirements.
• Adaption can reduce the computational time by adjusting the time step based on the CFL number, which is a measure of the stability and convergence of the solution. A higher CFL number means a larger time step and a faster simulation, but it may also cause numerical errors or divergence. A lower CFL number means a smaller time step and a more accurate simulation, but it may also increase the computational time. Adaption can find an optimal balance between accuracy and speed by changing the time step according to the solution behavior.

According to some of the web search results, adaption can result in up to 70% cell count reductions and up to 4X speed ups for steady state cases¹. You can also watch some of the video tutorials from the search results, such as How to Accelerate Ansys Fluent Simulations with Adaptive Meshing or CFL in adaptive time-step definition vs. max Cell Convective Courant number, to see some examples of how adaption affects the cell count and computational time in Ansys Fluent.

How does adaption affect the solution accuracy and convergence?

 Adaption can affect the solution accuracy and convergence in Ansys Fluent in the following ways:

• Adaption can improve the solution accuracy by resolving the flow features and capturing the physics more accurately. For example, adaption can refine the mesh in areas where the flow is turbulent, compressible, or reacting, and coarsen the mesh in areas where the flow is laminar, incompressible, or non-reacting. This can reduce the numerical errors and increase the confidence in the results.
• Adaption can improve the solution convergence by reducing the cell count and adjusting the time step. For example, adaption can coarsen the mesh in areas where the solution is smooth or less important, and refine the mesh in areas where the solution is complex or critical. This can improve the efficiency and stability of the simulation, as well as reduce the memory and disk space requirements.

How does mesh quality affect the solution accuracy and convergence?

Mesh quality is an important factor that affects the solution accuracy and convergence in Ansys Fluent, as it determines how well the mesh represents the geometry and the physics of the problem. The mesh quality can be measured by several parameters, such as skewness, aspect ratio, size change, and cell squish. These parameters indicate how distorted or stretched the cells are, and how far they deviate from the ideal shape. A good mesh should have low values of these parameters, as high values can cause numerical errors or instability in the solution.

According to some of the web search results, a good quality mesh can improve the accuracy and convergence of the solution in Ansys Fluent by:

• Resolving the flow features and capturing the physics more accurately. For example, a good mesh can refine the mesh in areas where the flow is turbulent, compressible, or reacting, and coarsen the mesh in areas where the flow is laminar, incompressible, or non-reacting. This can reduce the numerical errors and increase the confidence in the results¹.
• Reducing the cell count and adjusting the time step. For example, a good mesh can coarsen the mesh in areas where the solution is smooth or less important, and refine the mesh in areas where the solution is complex or critical. This can improve the efficiency and stability of the simulation, as well as reduce the memory and disk space requirements².

You can check and improve the mesh quality in Ansys Fluent using various tools and methods, such as:

• The Mesh Quality tool in Fluent Meshing, which can report and display the values of different mesh quality parameters for your mesh³.
• The Surface Mesh Improvement tool in Fluent Meshing, which can adjust the face quality limit and the collapse skewness limit to improve the surface mesh quality³.
• The Solution Adaption tool in Fluent, which can refine or coarsen the mesh based on gradients, errors, or regions of interest during the simulation⁴.
• The Solution History tool in Fluent, which can monitor and plot the residuals, forces, moments, or other quantities of interest during the simulation⁴.
• The Validation tool in Fluent, which can compare your results with experimental data or analytical solutions from various sources⁴.