Complex / adaptive geometries

Complex meshes can occur in a number of size ranges from the cooling system of a desktop PC over the interior of a sports car to modern architecture and entire mountain ranges. Complex forms in real-life environments often come with their own set of challenges for CFD simulation. On one hand, the number of total cells must not be so big to unduly increase the simulation time for a particular project, on the other hand - depending on the used solver model - the resolution needs to be high enough to ensure a high quality simulation.

Typically this is handled with various mesh refinement techniques, where particular parts of the geometry are resolved in greater detail than other parts. In most cases this will be surface cells, but sometimes also purely volumetric cells, for example when calculating site assessments for wind turbines. The situation is complicated by the fact that some solvers are sensitive to mesh size (e.g. certain Euler solvers) and mesh refinement factors (e.g. LES) and even more complicated when multiple layers of fluid/solid meshes are needed (e.g. for heat transfer simulations with fully resolved heat exchanger material).

We have experience in all these fields and take great care to ensure correct cell sizes in critical parts of the geometry to achieve accurate simulation results at feasible computational costs. We also do advanced refinements like for example simulating wind in a large area (several kilometres square) with an intransient solver to determine the average flow field and then use the result from this simulation as input for a transient (time dependent) simulation in a smaller region. Below you can find some examples.

Hexahedral mesh with complex terrain

Here is an example of a hexahedral mesh over a complex terrain for the LES (Large Eddy Simulation) of a wind turbine. More details can be found on our page about hexahedral and structured meshes.


 

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City block with buildings including round walls and holes

The mesh refinement of ground plane, walls and inlet layer in the video below show a fine resolution near surfaces and high velocity gradients. This allows full resolution of the curved wall elements, openings and architectural details, while still keeping a very reasonable cell count of ~14 Mio cells over a relatively large area (~1 Mio m²). There is also a video of a urban wind simulation done with this mesh.


 

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Car interior, air conditioning including driver and moisture transport