fsi2 harness: RTX_FSI2O_FILLET knob (the outline's fillet radius, 5 mm = t/2 in every recorded run: a half-round tip and 5 mm root fillets vs the reference's sharp rectangle; printed in both headers) — P5-3's first problem-definition probe after the h-term was traced to the wake's strength on the background

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01LzcjQX7tvgn87CQCyg9Cfr

crates/specialized/rtx-fsi/tests/fsi2_harness/overset.rs

@@ -45,6 +45,19 @@ fn patch_offset_h() -> f64 {
         .unwrap_or(6.0)
 }
 
+/// The outline's fillet radius (`RTX_FSI2O_FILLET`, metres; 5 mm = t/2 in
+/// every recorded run, so the tip is a full half-round and the root
+/// carries 5 mm fillets — the reference's flag is a sharp rectangle).
+/// P5-3's problem-definition probe: the tip's rounding sets how the flag
+/// sheds, i.e. the wake's strength, which the h-ladder says is the
+/// excitation that keeps growing.
+pub fn fillet() -> f64 {
+    std::env::var("RTX_FSI2O_FILLET")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(FILLET)
+}
+
 /// The patch's across stretch (`RTX_FSI2O_PATCH_STRETCH`, the geometric
 /// ratio of the outer to the wall cell, 4.0 in every recorded run): with
 /// 12 rows over 6 h the wall cell is 6 h (r − 1)/(r¹² − 1), r¹¹ = stretch —
@@ -286,7 +299,7 @@ impl OversetFluid {
             &interface.edges(&zero_d),
             FLAG_X1,
             h,
-            FILLET,
+            fillet(),
             patch_offset_h() * h,
             patch_rows(),
             patch_stretch(),
@@ -309,7 +322,7 @@ impl OversetFluid {
                 &interface.edges(&zero_d),
                 FLAG_X1,
                 h,
-                FILLET,
+                fillet(),
                 patch_offset_h() * h,
                 patch_rows(),
                 patch_stretch(),
@@ -640,7 +653,7 @@ impl OversetFluid {
         ) {
             let on_cyl =
                 ((centre[0] - CYL_CENTRE[0]).powi(2) + (centre[1] - CYL_CENTRE[1]).powi(2)).sqrt()
-                    < CYL_R + 1.5 * FILLET;
+                    < CYL_R + 1.5 * fillet();
             let near_tip = ((centre[0] - tip_mid[0]).powi(2) + (centre[1] - tip_mid[1]).powi(2))
                 .sqrt()
                 < 2.5 * FLAG_T;
@@ -787,7 +800,7 @@ impl OversetFluid {
             &self.interface.edges(d),
             FLAG_X1,
             self.h,
-            FILLET,
+            fillet(),
             patch_offset_h() * self.h,
             patch_rows(),
             patch_stretch(),

crates/specialized/rtx-fsi/tests/fsi2_harness/overset_march.rs

@@ -100,7 +100,7 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
     // Every setting the acceptance rule reads, printed once: P5-3 lost a
     // day to a floor of 2e-4 against the overnight marches' 1e-6.
     println!(
-        "  coupling: {} (reuse {}, ω0 {}, c1 {}), floor {:.1e}, rtol {:.1e}, stall accept {:.1e}, max subit {}, predictor {}, s = {}, patch offset {} h × {} rows, patch convection {:?}, bg convection {:?}, patch stretch {}",
+        "  coupling: {} (reuse {}, ω0 {}, c1 {}), floor {:.1e}, rtol {:.1e}, stall accept {:.1e}, max subit {}, predictor {}, s = {}, patch offset {} h × {} rows, patch convection {:?}, bg convection {:?}, patch stretch {}, fillet {} m",
         cfg.coupler,
         cfg.reuse,
         cfg.initial_relaxation,
@@ -116,6 +116,7 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
         super::overset::patch_convection(),
         super::overset::bg_convection(),
         super::overset::patch_stretch(),
+        super::overset::fillet(),
     );
 
     // Phase 1: rigid flag to t_release (`RTX_FSI2O_LOAD=dir` replaces the