Structured and Semi-Structured Blocks

Structured and semi-structured blocks can used locally to enrich the mesh with structured elements, or globally to create a fully structured mesh.

Local regions of hexahedral meshes of H-type can be added to the interior of the mesh (Floating), and they can also be attached to the geometry or existing blocks using the following types of connections.

Connection Option	Usage
Floating	The new block is a block that is not connected to the geometry, boundary layer mesh, or any existing blocks. The new block’s shape is a simple geometric shape like a cylinder or hexahedron.
Extended Hex Layers (EHL)	The new block starts from the outer surface of the boundary layer mesh generated on the panel. It is connected to 4-sided Struct Hex panels/superpanels or 2-, 3- or 4-sided Unstruct Hex panels/superpanels. It covers the entire panel area.
Extended Prism Layers (EPL)	The new block starts from the outer surface of the boundary layer mesh generated on the panel. It is connected to 2-, 3- or 4-sided Prism panels or superpanels. It covers the entire panel area.
Base Panels Connected	The new block starts from the panel surface and replaces the local boundary layer mesh. It is connected only to 4-sided panels or superpanels and creates a block of structured hexahedra directly connected to the panels. It covers the entire panel area.
Side Panels Connected	The new block is connected to Hybrid and/or Tetrahedra panels. Those panels do not have a boundary layer mesh generated started from them (e.g. panels with Symmetry boundary condition). It covers the entire panel area or just a portion of it.
Existing Blocks Connected	The new block is attached either to other connected blocks (e.g. EHL, EPL, Base Panel blocks) or to free blocks.
Cavity Block	The new block fills a cavity or other region with a fully structured mesh so that the boundary layer mesh in the adjacent region will not be interrupted by the presence of the cavity. A cavity block will have one or more of its faces defined as the Cavity Interface (its exposed faces). Hexahedral layers will be generated from the Cavity Interface during the generation of the typical boundary layer mesh and will be continuous with boundary layer mesh grown from adjacent wall panels. The Cavity option is usually chosen along with Base Panels. Blocks cannot have both Cavity and EHL connections.
Wake Block	The new block is attached to the trailing edge panels of the geometry. A wake block consisting of either hexahedra and/or prisms is created, depending on the shape of the selected panels and the element type chosen.
Swept Block	The new block is created by sweeping a surface mesh along a path defined by panels within the geometry. A swept block can start and/or end at an existing panel or a free surface. For blocks that start/end on a free surface, layers of prisms or hexahedra can be grown outward from this surface. The starting surface mesh may consist of either triangles or quadrilaterals.

Notes:

These local meshes can cover simple geometry volumes, while the more flexible hybrid meshes will cover the remaining of the domain.
Using the Base Panel option, Hex Blocks can also be used to completely fill simple cases with a purely hexahedral mesh.
Special care is taken in order to ensure a smooth coupling of the two types of meshes to make sure the sizes for both the structured and unstructured domains are compatible.
The mesh generator automatically takes care of interfacing the quadrilateral faces of the hexahedra with the triangular faces of the tetrahedra.
These connections can also be mixed together on a single block or multiple blocks as needed.
Blocks can either have straight sides or curved sides allowing for curved pipes to be filled with hexahedra.
Structured blocks (EHL, Base Panel, Cavity and Floating) can be exported as a structured set of nodes in ijk-notation.

When To Use

This meshing approach allows for certain flow features like vortices, wakes and mixing regions to be more accurately resolved through the use of aligned elements.

EHL blocks and EPL blocks allow local thickening of the prismatic boundary layer mesh to capture flow features like vortices, shocks and boundary layer separation.

Pure hexahedral meshes are also useful for simple configurations like ducts and pipes.

How to Use

Hex blocks are created using the options found in the Blocks/Hexahedra menu. The Create Block Wizard can also be started using the toolbar button. They can be exported as unstructured grid data or as IJK Hex blocks. Hex blocks can be re-used from one case to another through the usage of Hex Block (HXB) files or Hex Block Template (HBT) files. These files can be exported via Blocks>Save Block File (for HXB files) Blocks/Hexahedra>Block Templates>Save Block Template File… (for HBT files). The HXB file is used to save all blocks including blocks linked to panels. The block template (HXB) file is used to store the blocks in using block templates where blocks are linked to groups. Block templates can then be used to exchange blocks between cases that are similar, but do not have the same panel numbering. Either file format enable blocks to be used in a scripting environment.

Please see the following tutorials to learn how to use this feature:

Basic Extended Hex Layers (EHL) Block Tutorial – Basic EHL Technique
Advanced Extended Hex Layers (EHL) Block Tutorial – Advanced EHL Technique
Extended Prism Layers (EPL) Block Tutorial – EPL Technique
Free (Floating) Block with Side Panel and Hex Block Connections Tutorial – Free Floating Blocks with Side Panel and Hex Block Connections
All Hexahedra Tutorial – Creation of a Purely Hexahedral Mesh
All Hexahedra (Split Face) Tutorial – Creation of a Purely Hexahedral Mesh using Panel Splitting to create the proper block shapes
Advanced All Hexahedra Tutorial – More advanced techniques used to create a Purely Hexahedral Mesh for complicated geometries
Fill Gaps with Blocks (All Hexahedra) Tutorial – Creation of a Purely Hexahedral Boundary Layer Mesh and use of EHL blocks to fill the gap with hexahedra
Hexa Blocks for Pipes and Holes Tutorial – Using EHL blocks to fill a simple pipe (hole) with hexahedra
Cavity Blocks Tutorial – Using a Cavity Block to fill a slot with hexahedra without disturbing the boundary layer mesh.
Special Cavity Blocks Tutorial – Using Cavity Blocks to fill a cooling hole with hexahedra without disturbing the boundary layer mesh.
Swept Blocks Tutorial – Using a Swept Block to fill a curved hole geomtry.
Transition Blocks Tutorial – Use multiple block types to create a path of structured elements from the inlet to the outlet of a duct geometry with a circular inlet.