Tutorial 8: Creating Superblocks

Tutorial 8. Part 2. Using the Merge Block Utility

Step 1. Understanding Basic Block Structure

When a grid is created, GridPro creates the grid in elementary blocks based on the topology design. The user can merge these elementary blocks into larger “superblocks” based on predefined criteria and the GridPro algorithm developed by Dr. Rigby, Dr. Steinthorsson and W. Coirier at the NASA Lewis Research Center. Each block in GridPro has 6 unique faces and each block is connected to adjacent blocks by patches which function as a glue binding faces together. Two adjacent faces that belong to separate blocks will share a patch that will allow the two blocks to communicate. This connectivity functions as a “glue” and is saved into the blk.tmp.conn file that is automatically created as a result of the gridding algorithm. In order to merge two block faces that share a patch, the patch must be equal to or smaller than the cross sectional area of the adjacent block faces. The arrangement of the block faces and patches is shown in the picture below.

Step 2. Basic Merge

The basic merge command to by typed at the prompt is: mrgb file_name [options] If we want to carry out a merge procedure in GridPro format based on our property file, typing in the command without the options will merge all blocks with a similar property. Let’s merge the same grid as we did in Part I and take a look at the results. Save the grid as blk_basic.tmp, start GridPro, load in the grid file named Tutorial_8_blk and enter the PDC property setter.

Step 3. Merge Criteria

The merge routine can merge elementary blocks into super blocks based on user defined criteria. The syntax for this criteria is: mrgb file_name [options]

The four global criteria that control the merge operation are:
1) Superblock Properties
2) Faces
3) Patches
4) Surfaces created in the topology builder
When the merge routine begins, GridPro will output the merge criteria based on the user options. Below is an example of the basic merge that we conducted above.

Step 4. Merge Block Options

Graphics that illustrate the merge block features will help the user speed up his/her understanding of what kind of superblock grids that can be created. A number of options can be chosen by the user to create superblocks in a desired format.

Step 5. Limiting Number of Merged Blocks

The user can limit the number of blocks to be merged by using the Setting Block Number Limits.

Step 6 Merge Block with Face Properties

The user can control the merge block routine by specifying the face properties. Load the grid into the property setter and set two faces on the side as a PDC user5 property in the 2D Property Setter. The remaining faces will be set at their default values.

Step 7. Merge using Internal Surfaces

The user can choose whether internal surfaces should be used as a way to restrict the merge process (internal surfaces are those created in the Topology Builder).

Step 8. Scheduled Merge

GridPro allows the user to merge blocks using a predefined routine created in previous runs. As stated above, the schedule merge data is saved in the file_name.conn_m file.