Geometry creation for body-fitted fluid meshing

A body-fitted fluid mesh requires a solid body that represents the fluid volume. To model this fluid, you must mesh the void between the solid bodies and to mesh the void, you must create a solid body that occupies the void.

You use Pre/Post tools to create a body-fitted fluid mesh in the FEM file. These meshing tools are the same tools you use to create a structural mesh. However, when you use the flow solver, the available elements, element attributes, and mesh defaults are tailored to the flow analysis environment.

Building complex solid bodies for flow modeling

In Modeling, you must create or arrange several solid bodies to replicate the physical space occupied by a single fluid. These solid bodies must adhere to the requirements of the flow mesh.

You can use any solid modeling technique to build complex fluid bodies for the flow model:

• Create two solid bodies and unite, subtract, or intersect them.

• Create two solid bodies and translate or rotate them so that they have a pair of coplanar surfaces. The surfaces do not need to be the same size.

• Sketch, then extrude or revolve the sketch to create a body.

In Pre/Post, you can use the Surface Wrap commands to generate a polygon surface wrap body and its associated 2D mesh from regular polygon bodies, which represent the solid bodies.

Faces for 2D flow simulation objects

In the 3D flow model, you are not required to create 2D meshes on surfaces of 2D simulation objects, because they are defined by selecting polygon faces, which are in contact with 3D fluid elements.

When your existing polygon, boundary or internal, faces do not match the size and position of the 2D entity you want to define, you can define polygon faces for simulation objects by dividing faces in Modeling.

Faces for modeling convection

The flow and thermal solvers exchange information on flow surfaces where convection occurs. You mesh these flow surfaces with 2D solid elements for automatic detection of flow surfaces, or define Flow Surface simulation objects on the faces of the fluid polygon body. In some cases, you must create additional surfaces to delimit a flow surface, particularly when they are surrounded by the fluid.

Since the polygon faces define the location and extent of the convecting surface, the faces, from which they originate, must be created and constrained carefully in Modeling. A Flow Surface simulation object defined on a polygon face is fully associative with that face. If you modify the dimensions of a face, a part update automatically modifies the selection in the Flow Surface simulation object to reflect the change.

Create faces in Modeling on which to define a Flow Surface by combining the following techniques:

• Using Boolean operations to create two bodies with shared faces.

• Dividing a face shared by two bodies of the part.

Body-fitted meshing between fluid bodies

With body-fitted fluid meshing, the basic rule is that fluid can only pass from one fluid domain to another if the faces of the 3D flow elements are co-planar at the interface. For greatest accuracy and performance, the adjacent faces should have coincident nodes. The Mesh Mating Condition command ensures that nodes are coincident at the interface between two fluid bodies. The flow solver uses the coincident nodes to join the two fluid volumes at the interface, recognizing them as a single fluid domain.

When a mismatch occurs between the adjacent faces at the interface where mesh mating is not possible, the flow solver can still recognize the two fluid bodies as a single fluid domain. However, the flow coupling across the mismatched element faces results in some loss of accuracy and performance.

Depending on the flow solver, you activate the joining of fluid volumes with mismatched meshes at interface as follows:

• For the serial flow solver, select the Connect Disjoint Fluid Meshes check box on the 3D Flow page in the Solution dialog box.

• For the parallel flow solver, define the Disjoint Fluid Mesh Pairing simulation object at the interface between the two adjacent faces.

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Geometry creation for body-fitted fluid meshing, Simcenter 3D 2021.1 Series

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