R4-i + R5 design pass: RTX_FSI2O_REGEN_ONCE (one patch regeneration per coupled step; dies at step 0 — the registered test is void), the step CSV's subit/dres_y/dres_norm/fx_nodal/fy_nodal columns; the cut predictor's per-face term probe (enable_term_probe) and the curved instrument's exact side/wall viscous integrals — the static convex wall's flat residual is the viscous closure's first-order relative accuracy on O(1/h) fluxes

Co-Authored-By: Claude Fable 5.1 <[email protected]>

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/cut_predictor.rs

@@ -111,7 +111,8 @@ impl Solver {
         let cv = mask.cv_geometry(c, p);
         // S2-7b: the convective sides' own apertures (host prototype).
         let conv_parts = if mask.conv_sides_exact {
-            mask.cut().and_then(|cut| mask.exact_cv_side_parts(cut, c, p))
+            mask.cut()
+                .and_then(|cut| mask.exact_cv_side_parts(cut, c, p))
         } else {
             None
         };
@@ -159,7 +160,9 @@ impl Solver {
                     // The two half faces' own apertures times their faces' values.
                     let v = |q: [i64; 3]| val(d, q).unwrap_or(0.0);
                     (
-                        0.5 * (parts[d][1].0 * v(add(cell_minus, ed, 1)) + parts[d][1].1 * v(add(cell_plus, ed, 1))) * a_d,
+                        0.5 * (parts[d][1].0 * v(add(cell_minus, ed, 1))
+                            + parts[d][1].1 * v(add(cell_plus, ed, 1)))
+                            * a_d,
                         0.5 * (parts[d][0].0 * v(cell_minus) + parts[d][0].1 * v(cell_plus)) * a_d,
                     )
                 }
@@ -260,7 +263,8 @@ impl Solver {
                     return 0.0;
                 }
                 let cvq = mask.cv_geometry(c, q);
-                let ubq = mask.surface_velocity_at(body, foot_of(q, lat.face_position(c, q)), c, t_old);
+                let ubq =
+                    mask.surface_velocity_at(body, foot_of(q, lat.face_position(c, q)), c, t_old);
                 // Explicit, with a coefficient ∝ 1/d_f: take the gradient from
                 // the faces at least TRANSVERSE_DISTANCE_FLOOR h off the wall —
                 // a FULL neighbour too, over its own distance along the cut
@@ -426,6 +430,23 @@ impl Solver {
             + wall_rhs)
             / (inertia + shear + wall_implicit);
         let v_alpha = fraction * h[c] * area[c];
+        if let Some(tp) = self.term_probe.borrow_mut().as_mut() {
+            let m = rho * v_eff;
+            let terms = [
+                -conv / m,
+                diff / m,
+                (shear * (ub - u_star) - shear_explicit) / m,
+                pressure / m,
+                source / m,
+                (wall_rhs - wall_implicit * u_star) / m,
+                (u_star - u0) / dt,
+            ];
+            let v = &mut tp[c];
+            if v.len() <= idx_f {
+                v.resize(idx_f + 1, [0.0; 7]);
+            }
+            v[idx_f] = terms;
+        }
         (u_star, rho * (v_eff - v_alpha) * (u_star - u0) / dt)
     }
 }

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/mod.rs

@@ -230,7 +230,8 @@ impl Default for Parameters {
                 .is_ok_and(|v| v == "off"),
             // ON by default since S2-7 (`=h` reproduces the records before it).
             wall_exchange_axis: std::env::var("RTX_E3_WALL_EXCHANGE").map_or(true, |v| v != "h"),
-            wall_exchange_foot: std::env::var("RTX_E3_WALL_EXCHANGE").is_ok_and(|v| v == "axisfoot"),
+            wall_exchange_foot: std::env::var("RTX_E3_WALL_EXCHANGE")
+                .is_ok_and(|v| v == "axisfoot"),
             conv_sides_exact: std::env::var("RTX_E3_CONV_SIDES").is_ok_and(|v| v == "exact"),
             wall_flux_true_normal: std::env::var("RTX_E3_WALL_FLUX").is_ok_and(|v| v == "true"),
             wall_foot_centroid: std::env::var("RTX_E3_WALL_FOOT").is_ok_and(|v| v == "centroid"),
@@ -238,7 +239,8 @@ impl Default for Parameters {
             momentum_volume_tiled: std::env::var("RTX_E3_MOMENTUM_VOLUME")
                 .is_ok_and(|v| v == "tiled"),
             cv_sides_exact: std::env::var("RTX_E3_CV_SIDES").is_ok_and(|v| v == "exact"),
-            wall_order2_centroid: std::env::var("RTX_E3_WALL_ORDER2").is_ok_and(|v| v == "centroid"),
+            wall_order2_centroid: std::env::var("RTX_E3_WALL_ORDER2")
+                .is_ok_and(|v| v == "centroid"),
             // ON by default since S2-5 (`=0` reproduces the records before it).
             diffusion_centroid: std::env::var("RTX_E3_DIFFUSION_CENTROID")
                 .map_or(true, |v| v != "0"),
@@ -269,6 +271,11 @@ pub struct Solver {
     /// cut predictor only): the box route counts it, the operator route
     /// does not.
     pub(super) floor_source: std::cell::Cell<[f64; 3]>,
+    /// R5 design-pass instrument (host cut predictor only): per unknown
+    /// face of each component, the last step's momentum terms as
+    /// accelerations `[−conv, diff, wall shear, pressure, source, solid
+    /// exchange, total] / (ρ V_eff)`; `None` (the default) records nothing.
+    pub(super) term_probe: std::cell::RefCell<Option<[Vec<[f64; 7]>; 3]>>,
     /// The closure lag of the pressure corrections over the last step
     /// (`Mask::closure_lag` summed over the correctors; host path).
     pub(super) pressure_lag: std::cell::Cell<[f64; 3]>,
@@ -308,6 +315,7 @@ impl Solver {
             params,
             momentum_source: None,
             floor_source: std::cell::Cell::new([0.0; 3]),
+            term_probe: std::cell::RefCell::new(None),
             pressure_lag: std::cell::Cell::new([0.0; 3]),
             vol_old: Vec::new(),
             apertures_old: None,
@@ -402,6 +410,16 @@ impl Solver {
         .expect("embedded mask")
     }
 
+    /// R5 instrument: record the cut predictor's momentum terms per face
+    /// from the next step on (host path only; a no-op on the device path).
+    pub fn enable_term_probe(&self) {
+        *self.term_probe.borrow_mut() = Some([Vec::new(), Vec::new(), Vec::new()]);
+    }
+    /// The recorded terms per component face index (see `term_probe`).
+    #[must_use]
+    pub fn term_probe(&self) -> Option<[Vec<[f64; 7]>; 3]> {
+        self.term_probe.borrow().clone()
+    }
     /// The small-cell floor's momentum source over the last step (a force
     /// on the fluid; host cut predictor only, zero otherwise).
     #[must_use]