From da502b9f17b6633e0b33430f0930a25906ec7308 Mon Sep 17 00:00:00 2001
From: shaia <shaia@outlook.com>
Date: Sat, 4 Apr 2026 20:59:18 +0300
Subject: [PATCH] Fix adiabatic BC corner overwrites in natural convection test

Adiabatic top/bottom wall BCs were overwriting corner cells that
belong to the hot/cold Dirichlet sidewalls. Restrict adiabatic
Neumann copies to interior columns (i=1..nx-2) so sidewall
temperatures are preserved at corners.
---
 tests/validation/test_natural_convection.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tests/validation/test_natural_convection.c b/tests/validation/test_natural_convection.c
index 668cbdf..2ff959e 100644
--- a/tests/validation/test_natural_convection.c
+++ b/tests/validation/test_natural_convection.c
@@ -87,11 +87,14 @@ static void apply_cavity_bcs(flow_field* field, size_t nx, size_t ny) {
         field->v[j * nx + (nx - 1)] = 0.0;
     }
 
-    for (size_t i = 0; i < nx; i++) {
+    for (size_t i = 1; i < nx - 1; i++) {
         /* Bottom wall: adiabatic (Neumann dT/dy=0 via copy from interior) */
         field->T[0 * nx + i] = field->T[1 * nx + i];
         /* Top wall: adiabatic */
         field->T[(ny - 1) * nx + i] = field->T[(ny - 2) * nx + i];
+    }
+
+    for (size_t i = 0; i < nx; i++) {
 
         /* No-slip on top and bottom walls */
         field->u[0 * nx + i] = 0.0;