Negative Streamwise Force (CFx) for Imported 3D Wing Geometry Despite Physically Reasonable Pressure Distribution

[MartinG-ux]

Hi everyone,

I'm developing a Python-based aerodynamic framework that automatically generates a parametric 3D wing, meshes it with Gmsh, and runs SU2. I've encountered an issue where the integrated streamwise force is negative, even though the solution appears physically reasonable.

Environment
SU2: v8.4.0 Harrier (Windows MPI)
Gmsh: 4.14.1
Geometry generation: Python + CadQuery
CAD export: STEP
Mesh generation: Gmsh OCC
Solver: Euler
Flow:
Mach = 0.3
AoA = 5°
Geometry:
NACA 2412
Half-wing
Root symmetry plane
Closed wing tip
Closed trailing edge
Automated Pipeline
Wing Parameters
↓
Python Geometry
↓
CadQuery Loft
↓
STEP Export
↓
Gmsh importShapes()
↓
Boolean Difference
↓
Automatic Boundary Classification
↓
SU2 Mesh
↓
Generated config.cfg
↓
SU2_CFD

The pipeline is fully automated.

Mesh Verification
STEP imports successfully.
CAD solid is valid.
Positive solid volume.
Boolean difference succeeds.
One fluid volume is created.
Boundary classification:
Wing : 3 surfaces
Symmetry : 1 surface
Farfield : 6 surfaces
Gmsh reports no ill-shaped tetrahedra after optimization.
SU2 Configuration
SOLVER = EULER
MACH_NUMBER = 0.3
AOA = 5.0

MARKER_EULER = (Wing)
MARKER_SYM = (Symmetry)
MARKER_FAR = (Farfield)

MARKER_MONITORING = (Wing)

REF_AREA =
REF_LENGTH =
Observed Behaviour

The simulation runs normally and converges.

However, the integrated force in the freestream direction is negative.

Example:

CFx = -0.026
CD = -0.019

The pressure coefficient distribution appears qualitatively reasonable, and changing the angle of attack changes the lift direction as expected.

Verification Already Performed
Official SU2 tutorial (same installation) runs correctly and produces positive drag.
SU2 installation therefore appears to be working correctly.
Mesh quality has been checked.
Geometry is watertight.
STEP import succeeds.
Pressure field looks physically reasonable.
Lift changes with AoA as expected.
Reference area has been verified.
Question

Could this behaviour be related to:

face orientation after importing a STEP geometry,
Gmsh OCC surface orientation,
force integration on imported geometries,
or another issue that I may be overlooking?

I've attached a minimal reproducible example consisting of:

wing.step
fluid_domain.su2
config.cfg
history.dat
pressure coefficient screenshot

Any suggestions for additional diagnostics or likely causes would be greatly appreciated.

Thank you!
Minimal_Reproducible_file.zip

[pcarruscag]

And is the lift realistic?