Traditional pre-processors define a simulation model for a specific geometry or a mesh. When the geometry changes, the model set-up has to be adapted or, depending on the nature of the changes, completely redone. Abstract models define a simulation set-up in a geometry and mesh independent way, which makes Abstract Models re-usable for any product shape whether it differs just minimally or radically.
In an Abstract Model, material information, volume and boundary conditions are applied to abstract (not explicit shapes) geometry classes instead of geometrical entities or mesh regions.
The real simulation model is created when an Abstract Model is combined with a CFD CAD model. In simulation model, these abstract classes get associated with the real geometry entities by matching strings attached on real geometry entities with name of abstract geometry classes. This real simulation model is used for automatic mesh generation, application of all necessary material information, boundary- and volume-conditions as well creation of the CFD solver input deck.
The creation and testing of Abstract Models requires CFD expertise and is done by analysts; the use of Abstract Models needs no CFD knowledge. Selecting a best practice Abstract Model and relevant CAD geometry to work with is all that a designer has to do to get a reliable CFD simulation started.
Importing CAD geometry into a pre-processor can be very time-consuming when the geometry kernels of the CAD system and CFD pre-processor are not identical. Adding to this problem is the fact that whenever the CAD design is changed, the same process has to be repeated.
FluidNexus/AcuNexus avoids these efforts by using only the CAD system for all geometry related tasks, as well as for meshing. The CAD model is the reference geometry representation, no translated otherwise derived geometry models exist. Having only one geometry representation not only eliminates conversion and healing problems, but it also eliminates the possibility of having unsynchronized geometry versions.
To enable the use of a CAD model by FluidNexus/AcuNexus, simulation relevant volumes and surfaces need to be tagged with simulation text strings. The text strings allow FluidNexus/AcuNexus to apply the desired material models, volume or boundary-conditions and create a mesh according to the best practices for the simulation type at hand.
Mesh quality plays an important role to ensure robust execution of simulations and for the quality of CFD results. FluidNexus/AcuNexus offer users many capabilities to create meshes most suitable for a specific type of application and for the solver type involved.
Mesh parameters are defined in an abstract model allowing for re-use with varying geometries. The available control parameters include for instance: mesh size (absolute and relative to model size), curvature adaptation and multiple options for boundary layer definition (prism and tetrahedral).