Dynamic Mesh CFD Simulation

What is Dynamic Mesh?

In some cases, the shape of the mesh and the domain can change due to the shifting of borders over time. Also, in steady-state cases, the mesh form may be altered during the solution for reasons beneficial to the numerical solution.

These changes are referred to as dynamic mesh. It should be noted that in a dynamic mesh, the mesh cells can be moved, change their shape and size, and their number can increase or decrease. To use a dynamic mesh, you need to introduce a starting volume mesh and specify the characteristics of each moving zone.

 

Dynamic Mesh Applications

Dynamic mesh can be used wherever a domain boundary is moved. Here we will examine some of these issues

Automotive Engineering

The piston inside the cylinder of the internal combustion engine moves and the volume changes regularly. CFD simulation of an internal combustion engine is done with dynamic mesh.

 

Turbomachine Design

In all turbomachines, the blades move and the simulation range is constantly changing. One of the ways of ANSYS Fluent CFD simulation for such problems is to use dynamic mesh. Another way is to use the Multiple Reference Frames (MRF) and Single Reference Frame (SRF)

 

Biomedical Applications

The heart changes shape to pump blood. Dynamic mesh is used for CFD simulation of this phenomenon due to the change of shape in the domain.

 

Structural Analysis

Due to the movement of fluid and the forces caused by it, in some cases, structures change shape. Such simulations are called Fluid-Structure Interactions and dynamic mesh is used in them.

Dynamic mesh window in ANSYS Fluent

 

Dynamic Mesh Methods in ANSYS Fluent

The mesh methods offer different ways to update the mesh after each change.

Smoothing

In this method, the number of cells and their connection does not change. This method itself consists of several other methods, including spring/Laplace/boundary layer, diffusion, linearly elastic solid, and radial basis function.

 

Layering

In prismatic meshes such as wedge or tetrahedral, this method is used to reduce or add a layer of cells in the neighborhood of the moving boundary.

 

Remeshing

When the displacement of the boundary is larger than the local mesh, the quality of the cells may decrease. This leads to wrong results in calculations and convergence problems.

To solve this problem, Fluent identifies the cells that make the problem and re-meshes their location. When you use the remeshing method, it is recommended to use the unified remeshing method. In this way, the original mesh distribution is tried to be preserved. This method reduces the computational cost.

 

Dynamic Mesh Options in ANSYS Fluent

To the right of the dynamic mesh settings, there are options that specify dynamic mesh models.

In-cylinder

This model is only for transient problems. A in-cylinder dynamic mesh model focuses on the simulation of fluid flow around a cylindrical body that may be moving or deforming, which has applications in many devices such as automobiles. The interior of an internal combustion engine cylinder, is a good choice to simulate with this model. because the solution domain changes with the movement of the piston.

In-cylinder dynamic mesh is used to simulate combustion inside the cylinder of an internal combustion engine car. As the piston moves, the simulation domain changes.

 

Six Degree of Freedom (DOF)

In this model, at every moment, different forces acting on moving rigid bodies are calculated. These forces are calculated using pressure and shear force on objects. In this model, the equations of motion and rotation of the rigid body are solved along with calculations related to fluid flow. 6 degrees of freedom include displacement and rotation in three directions of Cartesian axes. In the 6 DOF model, if needed, movement and rotation can be limited in several or one axis.

 

Implicit update

We use this model whenever we want the mesh to be updated in each time step. This model is used for cases where the mesh movement depends on the fluid flow, for instance for Fluid-Structure Interaction simulation.

 

Contact Detection

This model allows the simulation to detect when two or more geometries, such as a moving object and a fixed boundary or other moving parts, come into contact, and enables the mesh to maintain mesh accuracy and quality accordingly.

Velocity ​​contour. In this simulation, the shape of the foil changes with the movement of the fluid flow, so dynamic mesh is used. Adopted from “Dynamic Mesh for Wavy Foil CFD Simulation”

 

CFDLAND expertise in Dynamic Mesh Modeling Using ANSYS Fluent Software

We explained how complex and extensive dynamic mesh is. Our experts at CFDLAND have done many CFD dynamic mesh simulations, some of which you can see at the top of this page. Learning dynamic mesh is very time-consuming and requires a lot of experience and trial and error. Don’t worry, we are here to help you. Order ANSYS Fluent CFD simulation from us. Be sure of the quality of our work.