overset mesh: the flat-tip outline (P5-3 option B) — cylinder_flag_outline_deformed_tip / cylinder_flag_patch_deformed{,_from}_tip take the tip's corner radius (t = the recorded semicircle, bit for bit; smaller = the benchmark's flat face between corner arcs sampled at the wall spacing, point count fixed across the deformation, the tip's corners kept off the hull source); pins: corner t reproduces the recorded outline, the 2.5 mm outline has the exact area excess with no collapsed spacing, the O-grid builds straight and at ± 80 mm cold and warm at ny 41/62; harness knob RTX_FSI2O_TIP_CORNER (default 0.01) on the cold and warm builds, printed in both headers; pinned-toolchain fmt on touched crates

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

@@ -13,7 +13,7 @@ use std::sync::{Arc, RwLock};
 
 use nalgebra::Vector3;
 use rtx_cfd::mesh::PatchSide;
-use rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed;
+use rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed_tip;
 use rtx_cfd::solvers::incompressible::{
     AleBoundaries, ConvectionScheme, CurvilinearParameters, CurvilinearPisoSolver,
     EmbeddedParameters, EmbeddedPisoSolver, FlowField, MgPrecision, NormalDiffusion, OversetField,
@@ -45,6 +45,17 @@ fn patch_offset_h() -> f64 {
         .unwrap_or(6.0)
 }
 
+/// The tip's corner radius (`RTX_FSI2O_TIP_CORNER`, metres; the recorded
+/// outline is the full semicircle, corner = t = 0.01): P5-3 option B — the
+/// benchmark's flat tip with rounded corners (2.5 mm) against the
+/// semicircle, gated on the lift phase and the per-period amplitude.
+pub fn tip_corner() -> f64 {
+    std::env::var("RTX_FSI2O_TIP_CORNER")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(FLAG_T)
+}
+
 /// 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).
@@ -292,7 +303,7 @@ impl OversetFluid {
             }
         });
 
-        let (cold_mesh, _) = cylinder_flag_patch_deformed(
+        let (cold_mesh, _) = cylinder_flag_patch_deformed_tip(
             CYL_CENTRE,
             CYL_R,
             FLAG_T,
@@ -304,6 +315,7 @@ impl OversetFluid {
             patch_rows(),
             patch_stretch(),
             sweeps,
+            tip_corner(),
         )?;
         // With the warm-started regeneration (`RTX_FSI2O_WARM_SWEEPS`), the
         // march starts on the converged fixed point of the warm build's
@@ -314,7 +326,7 @@ impl OversetFluid {
             .unwrap_or(0);
         let start_mesh = if warm_sweeps > 0 {
             let t0 = std::time::Instant::now();
-            let (m, (it, last)) = rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed_from(
+            let (m, (it, last)) = rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed_from_tip(
                 Some(&cold_mesh),
                 CYL_CENTRE,
                 CYL_R,
@@ -327,6 +339,7 @@ impl OversetFluid {
                 patch_rows(),
                 patch_stretch(),
                 20_000,
+                tip_corner(),
             )?;
             println!(
                 "  warm base: {it} sweep+respace iterations (last move {last:.1e}) in {:.1} s; {warm_sweeps} per regeneration",
@@ -788,7 +801,7 @@ impl OversetFluid {
     /// The patch around the interface `d`.
     pub fn patch_for(&self, d: &[f64]) -> CfdResult<rtx_cfd::mesh::PatchMesh> {
         let start = std::time::Instant::now();
-        let (mesh, _) = rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed_from(
+        let (mesh, _) = rtx_cfd::mesh::patch_gen::cylinder_flag_patch_deformed_from_tip(
             if self.warm_sweeps > 0 {
                 self.warm_base.as_ref()
             } else {
@@ -809,6 +822,7 @@ impl OversetFluid {
             } else {
                 self.sweeps
             },
+            tip_corner(),
         )?;
         self.regen_count.set(self.regen_count.get() + 1);
         self.regen_seconds

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 {}, fillet {} m",
+        "  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, tip corner {} m",
         cfg.coupler,
         cfg.reuse,
         cfg.initial_relaxation,
@@ -117,6 +117,7 @@ pub fn run_march_overset(case: BenchmarkCase, config: &OversetMarchConfig) -> Ov
         super::overset::bg_convection(),
         super::overset::patch_stretch(),
         super::overset::fillet(),
+        super::overset::tip_corner(),
     );
 
     // Phase 1: rigid flag to t_release (`RTX_FSI2O_LOAD=dir` replaces the