Hello,
in a Finite Volume based software like Ansys Fluent, what is the difference between structured and unstructured mesh ? And what are exactly are they ?
I searched through the Internet, but unfortunately could not understand it good.
I would appreciate if you could help.
As mentioned, the structural mesh will not be used in the present work and unstructured mesh will be a possible alternative. There are different options to create an element through CFD simulation used for creating different element types such as Point Element by Node, Line Element by Bar, Surface Element by Triangular element (Tri) and Quadrilateral element (Quad).While volume can be represented by a Tetrahedral element(Tetra) which has four tri faces (may be used in surface mesh), a Prism element has two tri faces and three quad faces, Pyramid element has four tri faces and one quad face. A hexahedral element has six quad faces (Hexa).
A general FV-based code does not make differences between structured and unstructured grids. It works by doing a flux reconstruction on each face of the finite volume, whatever its shape is.
Thus, you should rather focus on the grid generation issue. Structured grids are ordered-type by indices such (i,j,k) so that any value for these integers correspond to a spatial location and its topology is easily associated to next indices. Unstructured grids have not such ordering, therefore a node is associated to a single integer index and the topology is known by associating the connections of the node with the neighbouring nodes.
(I) Structured Meshing
In this approach, the governing equations transformed into the curvilinear coordinate system aligned with the surface. It is trivial for simple shapes. In structured–grid type there is an advantage and disadvantage, the advantage of this type is the easy nodal neighbour connectivity, which simplified programmed see figure 3.5. The disadvantage of this type is that they cannot be used for highly complex geometry (more complex than the flow over cylinder), another disadvantage is that when it is required to have concentration of point in one region (for reason of accuracy), unnecessary small spacing in other parts of the solution domain is produced, which is waste resources. Therefore, it excluded in this research.
(II) Unstructured Meshing
In this approach, the integral form of governing equations is discretized and either a finite-volume or finite-element scheme is used. This type of grid is best adapted for complex geometry discretization. It is the most flexible type that fit any arbitrary boundary. The advantage of this type is that it could be used with any discretization scheme. In addition, there is a large computational overhead owing to a large number of operations per node.
As mentioned, the structural mesh will not be used in the present work and unstructured mesh will be a possible alternative. There are different options to create an element through CFD simulation used for creating different element types such as Point Element by Node, Line Element by Bar, Surface Element by Triangular element (Tri) and Quadrilateral element (Quad).While volume can be represented by a Tetrahedral element(Tetra) which has four tri faces (may be used in surface mesh), a Prism element has two tri faces and three quad faces, Pyramid element has four tri faces and one quad face. A hexahedral element has six quad faces (Hexa).
I recommend you to visit next forum about it: https://www.cfd-online.com/Forums/cfx/19480-difference-between-structured-unstructured-mesh.html
The main difference between structured and unstructured meshes is that in unstructured meshes, the indices of the neighboring cells have to be stored for each cell. In a structured mesh, this is not necessary since, due to the structure, the indices of neighboring cells can be easily calculated.
Grids in structural form are identified by regular connectivity and the most common choices are quadrilateral in 2D and hexahedron in 3D. there is highly space efficient between nodes and another good thing with this form the convergence and good resolution. while, in unstructured form the connectivity of nodes irregular and it cost more time to computational solution and these grids usually involves triangles in 2D and tetrahedron in 3D.
Dear Seyed, following discussion, may help you to draw the comparison:
https://www.quora.com/What-are-the-points-of-comparison-between-a-structured-and-unstructured-mesh
http://imechanica.org/node/9864
http://www.cimec.org.ar/ojs/index.php/mc/article/viewFile/1289/1230
https://www.cfd-online.com/Forums/cfx/19480-difference-between-structured-unstructured-mesh.html
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