rtx-cfd: overset_cfd1 RTX_OVERSET_ROWS — the overlap depth (patch rows kept non-hole below the acceptor row, default 4) as a knob for the §5.11 band probe; saved-field tags carry it; rows ≤ 3 are refused by the map at ny = 41 (acceptor donors reach the hole at the flag tip)

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_0116sg1Qz1gMv9hdcKP1XUam

crates/specialized/rtx-cfd/tests/overset_cfd1.rs

@@ -25,6 +25,34 @@ const U_MEAN: f64 = 0.2;
 const REF_DRAG: f64 = 14.2929;
 const REF_LIFT: f64 = 1.11905;
 
+/// Tag of a settled-field set: resolution, scheme, and the overlap depth
+/// when it is not the default (`RTX_OVERSET_ROWS`).
+fn field_tag(ny: usize) -> String {
+    let rows = overlap_rows();
+    format!(
+        "ny{ny}_{}{}",
+        if std::env::var("RTX_OVERSET_CFD1_TVD").is_ok() {
+            "tvd"
+        } else {
+            "upwind"
+        },
+        if rows == OversetParameters::default().overlap_rows {
+            String::new()
+        } else {
+            format!("_rows{rows}")
+        }
+    )
+}
+
+/// `RTX_OVERSET_ROWS`: patch rows kept non-hole below the acceptor row
+/// (the overlap depth; default 4). The band probe of §5.11.
+fn overlap_rows() -> usize {
+    std::env::var("RTX_OVERSET_ROWS")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(OversetParameters::default().overlap_rows)
+}
+
 fn inflow(y: f64) -> f64 {
     1.5 * U_MEAN * y * (H - y) / (0.5 * H).powi(2)
 }
@@ -143,6 +171,7 @@ async fn run_cfd1(ny: usize, max_steps: usize) -> CfdResult<Cfd1> {
             .ok()
             .and_then(|v| v.parse().ok())
             .unwrap_or(OversetParameters::default().max_rounds),
+        overlap_rows: overlap_rows(),
         ..OversetParameters::default()
     };
     let mut solver = OversetPisoSolver::new(background, patch, (nx, ny, h, h), params)?;
@@ -182,14 +211,7 @@ async fn run_cfd1(ny: usize, max_steps: usize) -> CfdResult<Cfd1> {
     // run offline in seconds instead of the 20–50 min settle.
     let loaded = match std::env::var("RTX_OVERSET_CFD1_LOAD") {
         Ok(dir) => {
-            let tag = format!(
-                "ny{ny}_{}",
-                if std::env::var("RTX_OVERSET_CFD1_TVD").is_ok() {
-                    "tvd"
-                } else {
-                    "upwind"
-                }
-            );
+            let tag = field_tag(ny);
             let dir = std::path::Path::new(&dir);
             field.background = FlowField::load(&dir.join(format!("bg_{tag}.bin")))?;
             let read = |name: &str| -> Vec<f64> {
@@ -308,6 +330,11 @@ async fn run_cfd1(ny: usize, max_steps: usize) -> CfdResult<Cfd1> {
         .overlap()
         .region_force(&field.background, RHO, mu, |c| c == CellClass::Hole);
     let wall = load.total();
+    println!(
+        "    overlap rows {} (patch nn {})",
+        overlap_rows(),
+        solver.patch().mesh().nn()
+    );
     println!(
         "    momentum routes ny = {ny}: CV box ({drag_cv:.4}, {lift_cv:.4}) | ring outer ({:.4}, {:.4}) | hole boundary ({:.4}, {:.4}) | wall ({:.4}, {:.4}); defects [% of wall drag]: active {:+.2} fringe ring {:+.2} patch region {:+.2}",
         ring.0,
@@ -560,14 +587,7 @@ async fn run_cfd1(ny: usize, max_steps: usize) -> CfdResult<Cfd1> {
     // diagnostics without the march (background in `FlowField::save`'s
     // format; patch u, v, p as raw little-endian f64 vectors).
     if let Ok(dir) = std::env::var("RTX_OVERSET_CFD1_SAVE") {
-        let tag = format!(
-            "ny{ny}_{}",
-            if std::env::var("RTX_OVERSET_CFD1_TVD").is_ok() {
-                "tvd"
-            } else {
-                "upwind"
-            }
-        );
+        let tag = field_tag(ny);
         let dir = std::path::Path::new(&dir);
         std::fs::create_dir_all(dir).expect("save dir");
         field.background.save(&dir.join(format!("bg_{tag}.bin")))?;