rtx-cfd: overset momentum residual carries its pieces per ring face (time, convective, diffusive, pressure); overset_cfd1 offline probes on the saved fields — RTX_OVERSET_CFD1_FRONT dumps the cylinder-front faces by piece, RTX_OVERSET_CFD1_RAW re-evaluates the ring on the raw interpolated stamping without balance_fringe_fluxes (the balance is not the ring's source: +0.241 raw vs +0.247 balanced at ny = 41 upwind)

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01X2GmJXeQ2njUecEKiJZ1G2

crates/specialized/rtx-cfd/src/solvers/incompressible/overset/residual.rs

@@ -88,6 +88,9 @@ pub struct FaceResidual {
     pub r: f64,
     /// Between two fringe cells (else fringe–hole).
     pub fringe_fringe: bool,
+    /// The pieces of `r` (N/m): unsteady, convective, diffusive, pressure
+    /// (`r = time + conv − diff + pres`; upwind, interior faces).
+    pub pieces: [f64; 4],
 }
 
 /// The momentum residual by face class.
@@ -198,6 +201,55 @@ impl OversetPisoSolver {
         };
         let vol = dx * dy;
         let mut prescribed = Vec::new();
+        let mu = self.background.config().viscosity;
+        let upw = |f: f64, a: f64, b: f64| if f >= 0.0 { a } else { b };
+        // The upwind predictor's pieces on an interior u face, × ρ·vol.
+        let u_pieces = |m: &crate::solvers::incompressible::flow_field::FlowField,
+                        j: usize,
+                        i: usize| {
+            let (u, v) = (&m.u_old, &m.v_old);
+            let ue = 0.5 * (u[(j, i)] + u[(j, i + 1)]);
+            let uw = 0.5 * (u[(j, i - 1)] + u[(j, i)]);
+            let vn = 0.5 * (v[(j + 1, i - 1)] + v[(j + 1, i)]);
+            let vs = 0.5 * (v[(j, i - 1)] + v[(j, i)]);
+            let conv = (ue * upw(ue, u[(j, i)], u[(j, i + 1)])
+                - uw * upw(uw, u[(j, i - 1)], u[(j, i)]))
+                / dx
+                + (vn * upw(vn, u[(j, i)], u[(j + 1, i)]) - vs * upw(vs, u[(j - 1, i)], u[(j, i)]))
+                    / dy;
+            let diff = (u[(j, i + 1)] - 2.0 * u[(j, i)] + u[(j, i - 1)]) / (dx * dx)
+                + (u[(j + 1, i)] - 2.0 * u[(j, i)] + u[(j - 1, i)]) / (dy * dy);
+            let pres = (m.p[(j, i)] - m.p[(j, i - 1)]) / dx;
+            [
+                rho * (m.u[(j, i)] - m.u_old[(j, i)]) / dt * vol,
+                rho * conv * vol,
+                mu * diff * vol,
+                pres * vol,
+            ]
+        };
+        let v_pieces = |m: &crate::solvers::incompressible::flow_field::FlowField,
+                        j: usize,
+                        i: usize| {
+            let (u, v) = (&m.u_old, &m.v_old);
+            let vn = 0.5 * (v[(j, i)] + v[(j + 1, i)]);
+            let vs = 0.5 * (v[(j - 1, i)] + v[(j, i)]);
+            let ue = 0.5 * (u[(j - 1, i + 1)] + u[(j, i + 1)]);
+            let uw = 0.5 * (u[(j - 1, i)] + u[(j, i)]);
+            let conv = (vn * upw(vn, v[(j, i)], v[(j + 1, i)])
+                - vs * upw(vs, v[(j - 1, i)], v[(j, i)]))
+                / dy
+                + (ue * upw(ue, v[(j, i)], v[(j, i + 1)]) - uw * upw(uw, v[(j, i - 1)], v[(j, i)]))
+                    / dx;
+            let diff = (v[(j + 1, i)] - 2.0 * v[(j, i)] + v[(j - 1, i)]) / (dy * dy)
+                + (v[(j, i + 1)] - 2.0 * v[(j, i)] + v[(j, i - 1)]) / (dx * dx);
+            let pres = (m.p[(j, i)] - m.p[(j - 1, i)]) / dy;
+            [
+                rho * (m.v[(j, i)] - m.v_old[(j, i)]) / dt * vol,
+                rho * conv * vol,
+                mu * diff * vol,
+                pres * vol,
+            ]
+        };
 
         // u faces (j, i), i = 1..nx: cells (j, i−1) | (j, i).
         for j in 0..ny {
@@ -243,6 +295,7 @@ impl OversetPisoSolver {
                         i,
                         r,
                         fringe_fringe: w == CellClass::Fringe && e == CellClass::Fringe,
+                        pieces: u_pieces(&m, j, i),
                     });
                 }
             }
@@ -290,6 +343,7 @@ impl OversetPisoSolver {
                         i,
                         r,
                         fringe_fringe: s == CellClass::Fringe && n == CellClass::Fringe,
+                        pieces: v_pieces(&m, j, i),
                     });
                 }
             }