• For simple geometries, quad/hex meshes can provide higher-quality solutions with fewer cells than a comparable tri/tet mesh. Align the gridlines with the flow.

• For complex geometries, quad/hex meshes show no numerical advantage, and you can save meshing effort by using a tri/tet mesh.

Different types of meshes used in CFD

The following types of meshes are used in Computational Fluid Dynamics.

• Triangular mesh: mesh consisting entirely of triangular elements.
• Tetrahedral mesh: mesh with only tetrahedral elements.
•  Hybrid mesh: mesh with one of the following:
•  Triangles and quadrilaterals in 2D
•  Any combination of tetrahedral , prisms, pyramids in 3D
•  Non-conformal mesh: mesh in which grid nodes do not match up along an interface.
•  Hex-core mesh: mesh consisting of tetrahedral /prism elements next to boundaries and a Cartesian hexahedral mesh in the core flow regions

There are various reasons why CFD is becoming popular, some of which are:

• CFD allows numerical simulation of fluid flows, results for which are available for study even after the anaylsis is over. This is a big advantage over, say, wind tunnel testing where analysts have a shorter duration to perform flow measurements.
• CFD allows observation of flow properties without disturbing the flow itself, which is not always possible with conventional measuring instruments.
• CFD allows observation of flow properties at locations which may not be accessible to (or harmful for) measuring instruments. For example, inside a combustion chamber, or between turbine blades.
• CFD can be used as a qualitative tool for discarding (or narrowing down the choices between), various designs. Designers and analysts can study prototypes numerically, and then test by experimentation only those which show promise.
  

Source : CFD -wiki

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