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Dynamic meshing in ANSYS FLUENT
Dynamic meshing refers to situations in which the computational grid changes dynamically during the run of the CFD simulation. This opens up for the possibility to simulate flows where the geometry changes with time, e.g. flows around falling objects or internal combustion in cylinders.
For most CFD simulations the physical geometry does not change with time, and a steady mesh will then generally be the appropriate choice. For moving geometries, dynamic meshing becomes a necessary part of the modeling. Further, in many such cases it is not possible to determine the exact behavior of the geometry change a priori. A good example of this is a falling object that is subject to a transient flow. Since the object will affect the flow, and vice versa, it is not possible to determine the exact trajectory of the object before the simulation is run. A separate model is implemented interactively to calculate the fluid-object interaction “on-the-fly”. In the subsequent step, the mesh is updated.
The following example serves as an illustration of some of the features of dynamic meshing.
A triangular-shaped object is attached close to the ceiling of a wind tunnel. At a given instant, the object is released and falls towards the floor due to gravity. As the object enters the “wind section” of the wind tunnel it is accelerated by the flowing fluid and starts to move with it. The sequence is shown in video 1. Since it is not possible to determine the exact trajectory in advance, ANSYS FLUENT uses the object’s forces and moments to calculate the translational and angular motion of the center of gravity of the object at every time step. This is accomplished by the built-in 6dof (“six degrees of freedom”) solver. It then updates the mesh. The velocity contour of the flow is shown in video 2, and the mesh is dynamically updated as seen in video 3.
Video 1:
Video 2:
Video 3: