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Valeo chose Gridgen as a tool to help with the development of their fan system product line. Gridgen replaces the previous integrated meshing tools within CFX-TASCflow, which were based on parametric templates to create structured blocks and attach them together.
Input data are relatively limited, since no CAD geometries are available a priori for fans at the earlier stage of development, and for which performance has to be estimated before any physical prototype. ASCII files are simply used to describe the blade profile at different given radii from bottom to top, and the whole topology of the computational domain is extrapolated from these airfoil data by a program written in Fortran. The user specifies values for the numerous parameters which are used to describe the fan geometry (number of blades, hub and shroud diameter, etc.), to dimension the computational domain around the fan mimicking the experimental set-up (length of inlet and outlet domains) and to control the grid quality (thickness of “O-grid” around blade).
Resulting files describe the whole computational topology by curves and surfaces. They are read by Gridgen and converted into the native Pointwise database. All connectors are directly created from curves, whereas the number of nodes and their distribution is completely parameterized in the script. Domains and blocks can be easily built on the base of previous connectors and database surfaces.
All these operations have been scripted in GridgenGlyph files, which have been linked in a final command file. The objective is to have an automated meshing tool for fans. This last point is absolutely needed because meshes must be created iteratively and automatically in a short amount of time (few minutes), if several simulations must be launched everyday to create performance curves for the designer.
In parallel to the creation of such standard grids used daily for fan development, the database and the mesh previously described can also be used partially when there is a specific need for special geometries and more complicated fan system configuration. For instance, removing the rotating ring on the fan and replacing it by a more classical tip clearance between the blades and the stationary shroud requires only a few hours for an inexperienced user, while modifying the shape and the size of inlet or outlet domains can be done quickly.
In summary, Gridgen has provided significant improvement, especially regarding the following aspects:
- rapid training of the whole fan system group
- ability to manage complex geometries with structured or unstructured meshes
- smoothing capabilities with outstanding performance
- output format available for all commercial codes and main standards of the market
- possibility to script by Gyph command, which allows us to automatically create standard meshes
A first version of the GridgenGlyph script is already in production and used by the whole fan system group and gives the ability to create good quality meshes. The development of a second more advanced version is in progress, and should take more advantage of the extrusion tool (around the blade in particular) and Gridgen’s elliptic smoothing capabilities (in the blade to blade passage).
For more information about the script VALEO is using, please contact Yves-Marie Lefebvre at yves-marie.lefebvre@sirehna.com.
The script generates geometry for blades, hub, shroud, and inflow and outflow sections.
This fan grid was created automatically with Valeo's GridgenGlyph script.
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