FoilGrid User Manual · CAE Utilities

Last updated: 2026-10-09 25 min read

FoilGrid GUI generates an O-grid, C-grid, or C-H grid for a single airfoil, lets you inspect its quality, and exports a solver-ready CGNS or VTU mesh. This manual describes the user interface, the airfoil .dat input format, and the output conventions of the final mesh.

Quick Start
Airfoil DAT Input Format
TE Closure and Topology
Settings Panel
Render Toolbar and Quality Inspection
CGNS Output Conventions
Logs and Problem Reports

1. Quick Start

Open a .dat file with Open Airfoil, or create an analytic airfoil with Create Airfoil….
Select TE Closure and Topology to match the input trailing-edge shape.
Set the required grid resolution and wall spacing, then click Generate.
Inspect the grid lines and quality values. Invalid cells must be zero.
Click Export Mesh… to save the mesh. CGNS is the default GUI output format.

Coordinate convention
Unit-chord coordinates with LE ≈ (0, 0) and TE ≈ (1, 0) are recommended. FoilGrid does not automatically normalize or rotate coordinates loaded from a file.

Single-airfoil O-grid generated in FoilGrid GUI

Use the left panel to define the geometry, grid, and wall-spacing settings, and inspect the generated mesh and quality in the center view. If you change a setting, the previous mesh remains visible but is marked stale. It cannot be exported until you generate the mesh again.

2. Airfoil DAT Input Format

FoilGrid reads the XFOIL/Selig labeled coordinate format. The first non-comment line is the airfoil name. Enter whitespace-separated x y coordinates on the following lines.

text

# Full-line comments are allowed
NACA 0012
1.000000   0.001260   # TE upper
0.750000   0.031600
0.250000   0.059400
0.000000   0.000000   # LE
0.250000  -0.059400
0.750000  -0.031600
1.000000  -0.001260   # TE lower

The recommended coordinate order is:

text

upper TE → upper surface → LE → lower surface → lower TE

2.1 Supported Rules

Spaces, tabs, and floating-point values in decimal or scientific notation are allowed.
Blank lines and full-line or inline # comments are allowed.
A reversed point order is corrected using a heuristic based on the Y coordinates near the endpoints.
At least three points are required. At least 50 points are generally recommended for curvature reconstruction.
The number of input points is independent of Surface nodes in the GUI. The input curve is reconstructed and redistributed to the requested number of nodes.
The X-coordinate difference between the first and last points must not exceed 1e-9. An open TE may have different Y coordinates at the two endpoints, but their X coordinates must match.

2.2 Formats That Require Conversion

Format	Required preparation
Coordinate list without a header	Add one line containing the airfoil name; otherwise, the first coordinate is consumed as the name
Lednicer format	Remove the upper/lower point-count header and convert the coordinates into one continuous surface list
`!` comments	Replace them with `#` comments
Multi-element airfoil	The current GUI supports one continuous airfoil section only

If the X coordinates of the two TE endpoints do not match, Generate is disabled and the GUI displays instructions for correcting the input. When converting an input file, follow the supported rules and coordinate order above.

3. TE Closure and Topology

Input and closure	O-grid	C-grid	C-H grid
Open TE + Rounded	Supported, 1 block	Not supported	Not supported
Open TE + Flat	Supported, 1 block	Not supported	Supported, 4 blocks
Closed TE + Closed (sharp)	Supported, 1 block	Supported, 3 blocks	Interpreted as a C-grid, 3 blocks

O-grid: The simplest and most robust default. One periodic block surrounds the complete airfoil.
C-grid: Creates grid lines extending downstream from a closed, sharp TE.
C-H grid: Closes an open, blunt TE with a flat base and creates separate TE-base and wake blocks.
Rounded: Connects an open TE with a curve. The GUI allows this closure for O-grids only.

O-grid and C-H Grid with the Same Flat TE

O-grid	C-H grid

One block surrounds the entire shape.	Separate blocks connect the TE base and wake region.

O-grid and C-grid Examples by Solver

Topology	Elliptic	Hyperbolic
O-grid
C-grid

These figures illustrate how the outer boundary and grid-line distribution vary with solver and topology. The actual distribution also depends on the node counts, farfield size, wake settings, and Advanced options.

4. Settings Panel

The default values in collapsed sections are suitable for an initial grid in most cases.

4.1 TE Closure

Item	Description
Closed (sharp)	Use for input with an endpoint gap of `1e-9` or less
Flat	Connect an open TE with a flat base surface
Rounded	Connect an open TE with a curve; available for O-grids only
TE gap display	Shows whether the input is open or closed and reports the actual endpoint distance

4.2 Grid

Item	Description
Topology	Select O-grid, C-grid, or C-H grid
Solver	Select hyperbolic marching or elliptic smoothing
Surface nodes	Number of nodes around the airfoil after closure processing; independent of the DAT input point count
Normal nodes	Number of wall-normal nodes, including the wall and farfield rows
Farfield radius	Size of the outer boundary in the input coordinate system

4.3 LE / TE Spacing

Item	Description
LE spacing	Surface-direction spacing at the leading edge; a smaller value clusters more points at the LE
TE spacing	Surface-direction spacing at the trailing edge; also used to determine the number of closure points

When either value is zero, FoilGrid uses the automatically calculated value shown in the GUI. These values are spacings along the wall, not the height of the first wall-normal cell.

4.4 Wall Spacing

Method	Input	Description
From y+	y+, Reynolds, Reference chord	Calculate First height with a flat-plate correlation
First-layer height	Height	Enter the first wall-normal cell height directly

The calculated First height appears below the settings. Reference chord and a directly entered Height must use the same length unit as the airfoil coordinates.

4.5 Wake Settings

Item	Description
Wake nodes	Number of downstream wake nodes for C/C-H grids; not used for O-grids
Length factor	Length multiplier for the elliptic outer wake boundary
First-cell factor	First-spacing multiplier for the elliptic outer wake boundary

Length factor and First-cell factor apply to the elliptic outer wake boundary. They are disabled for the hyperbolic solver.

4.6 Advanced — Hyperbolic

Item	Actual role
Surface coupling (α)	Surface-direction coupling in the marching matrix; this is not a relaxation factor
Next-row smoothing	Reduces surface-direction irregularity in the displacement of the next row; its effect increases away from the wall
Current-row correction	Curvature correction for current-row coordinates; increasing it does not always produce a smoother grid
Outer-area uniformity	Blends the target cell area toward a uniform value near the farfield; a higher value preserves less surface clustering
Target-area passes	Number of neighbor-averaging passes applied to the target cell area at each marching step; it does not directly average coordinates
Block smoothing iterations	Elliptic smoothing budget after hyperbolic C/C-H blocks are connected; not used for O-grids

4.7 Advanced — Elliptic and Output Cells

Item	Actual role
Primary iterations	Initial elliptic iterations for an O-grid; included in the connected-block smoothing budget for C/C-H grids
Additional iterations	Additional smoothing after O-grid wall spacing is applied; added to the connected-block budget for C/C-H grids
Outer-boundary clustering	Circumferential distribution on an elliptic O-grid outer boundary; 1 is uniform and the option is not used for C/C-H grids
Triangulate (3D: prisms)	Split 2D quads into triangles, or 3D hexahedra into prisms

Change Advanced values one at a time from their defaults, then compare the grid lines and quality values for the same input.

4.8 3D Extrusion

Item	Description
Extrude to a 3D grid	Uniformly extrude the 2D mesh; generating a 3D grid automatically unlocks the 2D view
Length	Total extrusion distance
Divisions	Number of cells in the extrusion direction; the number of sections is `Divisions + 1`
Rotate output to Z-up (+Y → +Z)	Rotate 90° about +X so the airfoil thickness direction, +Y, aligns with global +Z

C-grid extruded to 3D and rotated to Z-up

The figure shows a C-grid extruded to 3D with Z-up rotation enabled. The number of sections in the extrusion direction is Divisions + 1, and the two end sections are exported as symmetry markers.

LE/TE spacing, first-cell height, Farfield radius, and extrusion Length all use the same length unit as the input coordinates.

2D view: Locks the camera to a +Z parallel projection and disables rotation. Pan, zoom, and fit remain available.
Surface: Shows cell faces only.
Surface with edges: Shows cell faces and grid lines.
Wireframe: Shows grid lines only.
Direction, rotation, and parallel-projection controls become available after you turn off 2D view.
Starting 3D generation automatically unlocks the 2D view.

5.2 Quality Values

Display	Meaning
Cells	Number of cells in the final exported mesh
Min Jacobian	Minimum scaled Jacobian; it must be positive, and a larger value is better
Max skewness	Equiangle skewness in `[0, 1]`; zero is ideal
Invalid cells	Number of cells with non-finite values or a scaled Jacobian ≤ 0; this must be zero before export

Do not rely on the numbers alone. Inspect the LE, TE, wake, and block interfaces for abrupt bends or sudden spacing changes. If invalid cells exist, the result remains visible for inspection, but Export Mesh… is disabled.

6. CGNS Output Conventions

CGNS is the default export format in the GUI, with VTU available as a secondary format. Interface nodes from the internal structured blocks are merged, and the final output is written as one unstructured zone.

Item	Output convention
Mesh name	`foilgrid`
Zone name	`fluid`
Default 2D cells	`QUAD_4`; `TRI_3` when Triangulate is enabled
Default 3D cells	`HEXA_8`; `PENTA_6` when Triangulate is enabled
2D coordinates	`z = 0`, cell dimension 2, physical dimension 3
Block interfaces	Shared nodes are merged to form a continuous mesh in the final zone

6.1 Boundary Markers and CGNS BC Types

Marker	CGNS BC type	Creation condition and meaning
`airfoil`	`BCWallViscous`	Airfoil wall in every topology
`te_base`	`BCWallViscous`	C-H base surface for an open, flat TE
`farfield`	`BCFarfield`	Farfield boundary, including the C/C-H outlet
`symmetry_low_z`	`BCSymmetryPlane`	Start section of the default 3D extrusion, `z = 0`
`symmetry_high_z`	`BCSymmetryPlane`	End section of the default 3D extrusion, `z = Length`
`symmetry_high_y`	`BCSymmetryPlane`	Start section after Z-up rotation, `y = 0`
`symmetry_low_y`	`BCSymmetryPlane`	End section after Z-up rotation, `y = -Length`

FoilGrid provides boundary names and CGNS BC types; it does not assign the solver's physical boundary-condition values. Verify that marker names and BC types map to the intended conditions when connecting the mesh to a solver.

6.2 3D Coordinate Axes

The default 3D mode uniformly extrudes the 2D grid in the +Z direction.
Cell spacing is Length / Divisions, and the number of sections is Divisions + 1.
With Rotate output to Z-up enabled, FoilGrid first applies (x, y, z) → (x, -z, y) and then extrudes in the -Y direction.
In Z-up mode, the original +Y airfoil thickness direction becomes global +Z.

7. Logs and Problem Reports

The Generation log records:

FoilGrid version, build type, Qt version, operating system, and CPU architecture
Input shape name, path, coordinate count, chord, thickness, and TE gap
Requested settings and the resolved topology, spacing, and grid dimensions
Engine debug, info, warning, and error messages
Block, node, and cell counts; quality values; and invalid-cell count
Boundary marker names, CGNS BC types, and zone connectivity
Export path, completion status, and file size

If you encounter a problem, click Copy Log in the Log panel and send the complete contents to [email protected].

Anonymous usage statistics can be disabled in the About dialog. Telemetry includes only the product version and build, OS, CPU, memory, and generation success or failure. It does not transmit airfoil data, meshes, file paths, or settings.

Automation through the CLI program is available through a separate sales channel. For customization or separate development, contact [email protected].

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