rtx-cfd: OverlapMap::region_force — momentum flux into a background region (control-volume face formula, one-sided next to holes); overset_cfd1 prints the four momentum routes (CV box, ring outer, hole boundary, wall) and their defects at the settled state

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

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

@@ -10,7 +10,7 @@
 use rtx_cfd::mesh::PatchSide;
 use rtx_cfd::mesh::patch_gen::cylinder_flag_patch;
 use rtx_cfd::solvers::incompressible::{
-    AleBoundaries, CurvilinearParameters, CurvilinearPisoSolver, EmbeddedParameters,
+    AleBoundaries, CellClass, CurvilinearParameters, CurvilinearPisoSolver, EmbeddedParameters,
     EmbeddedPisoSolver, FlowField, NormalDiffusion, OversetField, OversetParameters,
     OversetPisoSolver, PatchConvection, PatchField, PoissonSolverKind, SideBoundary,
 };
@@ -262,6 +262,29 @@ async fn run_cfd1(ny: usize) -> CfdResult<Cfd1> {
         .patch()
         .surface_force(&field.patch, PatchSide::Inner, solver.time());
     let (drag_cv, lift_cv) = cv_force(&field, &solver);
+    // P4 momentum-defect measurement: the force the background transmits
+    // into the ring (fringe + hole), into the hole alone, and the patch's
+    // wall force — consecutive differences are the active region's
+    // residual, the fringe ring's momentum defect, and the patch region's.
+    let ring = solver
+        .overlap()
+        .region_force(&field.background, RHO, mu, |c| c != CellClass::Active);
+    let hole = solver
+        .overlap()
+        .region_force(&field.background, RHO, mu, |c| c == CellClass::Hole);
+    let wall = load.total();
+    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,
+        ring.1,
+        hole.0,
+        hole.1,
+        wall[0],
+        wall[1],
+        100.0 * (drag_cv - ring.0) / wall[0],
+        100.0 * (ring.0 - hole.0) / wall[0],
+        100.0 * (hole.0 - wall[0]) / wall[0],
+    );
     Ok(Cfd1 {
         drag_surface: load.total()[0],
         lift_surface: load.total()[1],