Debug airfoil sign error

[danieljvickers]

Description

The levelsets of airfoils have a sign error, causing them to point into the aifoil rather than away. This causes the airfoil IB to suck in fluid rather than repel it. This is very evident in low mach numbers and causes instabilities.

Type of change

• Bug Fix

Checklist

• I added or updated tests for new behavior
• I updated documentation if user-facing behavior changed

See the developer guide for full coding standards.

GPU changes (expand if you modified src/simulation/)

• GPU results match CPU results
• Tested on NVIDIA GPU or AMD GPU

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[github-actions]

Claude Code Review

Head SHA: 418efe8

Files changed:

• 1
• src/simulation/m_compute_levelset.fpp

Findings

1. s_airfoil_levelset (2D): upper and lower surfaces now use opposing normal conventions

The PR reverses dist_vec for the lower surface only, leaving the upper surface unchanged. After this diff:

• Upper surface (unchanged): dist_vec = xy_local - airfoil_grid_u(global_id) — vector points from surface point toward ghost point (outward)
• Lower surface (changed): dist_vec = airfoil_grid_l(global_id) - xy_local — vector points from ghost point toward surface (inward)

Both branches feed directly into:

gp%levelset_norm = matmul(rotation, dist_vec(:))/dist

For a 2D airfoil, levelset_norm now points outward for ghost points above the chord line and inward for ghost points below it. This inconsistent sign on the lower-surface normal will corrupt boundary condition enforcement at those ghost points.

2. s_3d_airfoil_levelset (3D): all surface normals now point inward

Both the upper and lower branches of the 3D subroutine are flipped. The resulting dist_vec in every branch now points from the ghost point toward the nearest surface point (inward), and is stored directly as:

gp%levelset_norm = matmul(rotation, dist_vec(:)/dist_surf)

Every other geometry in this module (s_circle_levelset, s_sphere_levelset, s_rectangle_levelset, s_cuboid_levelset) builds dist_vec as ghost_point_position − surface_point_position, yielding an outward-pointing normal. The post-PR 3D airfoil normals are systematically reversed relative to the module convention, producing wrong wall-normal directions for IB boundary conditions in 3D.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.31%. Comparing base (7081882) to head (418efe8).

Files with missing lines	Patch %	Lines
src/simulation/m_compute_levelset.fpp	0.00%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1443   +/-   ##
=======================================
  Coverage   61.31%   61.31%           
=======================================
  Files          72       72           
  Lines       19771    19771           
  Branches     2852     2852           
=======================================
  Hits        12123    12123           
  Misses       5699     5699           
  Partials     1949     1949           

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[sbryngelson]

@danieljvickers have a look at the claude comments for a double check