embedded3 S2-6: the oblique-wall instrument (tests/embedded3_wall_position_oblique.rs: z-flow / in-plane Poiseuille + Couette linear exactness; gate oblique_wall_position_is_second_order) and the closures it found, host + device, default OFF — the transverse centroid correction (RTX_E3_DIFFUSION_TRANSVERSE=1, wall_order bit 7), the fine distance floor (RTX_E3_DISTANCE_FLOOR=fine, bit 8); kernel geometry factored into cut_cv; DFG 2D-1 x-shift knob (RTX_E3_DFG_SHIFT_X); FLAG_X0 0.6 -> 0.25 in the three flag tests (the flag of every record was detached)

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

crates/specialized/rtx-cfd/tests/embedded3_dfg_2d1.rs

@@ -47,6 +47,10 @@ fn dfg_2d_1_on_the_device() {
     let nz = NZ;
     let lz = nz as f64 * h;
     let t_end = env_f("RTX_E3_DFG_T", 10.0);
+    // S2-6: the body (and the Δp probes) shifted in x by a fraction of h —
+    // the lift's grid-registration scatter (a y-shift would change the
+    // physical lift: the cylinder is 5 mm off the centreline).
+    let cx = CX + env_f("RTX_E3_DFG_SHIFT_X", 0.0) * h;
     // Explicit stability: CFL 0.3 on U_m and half the viscous limit.
     let dt = (0.3 * h / U_M).min(0.5 * h * h / (6.0 * NU));
     let mut solver = Solver::new(
@@ -81,7 +85,7 @@ fn dfg_2d_1_on_the_device() {
     // traction route (S2-1).
     solver.set_body(Body::extruded(
         rtx_cfd::solvers::incompressible::EmbeddedBody::circle(
-            CX,
+            cx,
             CY,
             0.5 * D + env_f("RTX_E3_DFG_DR", 0.0) * h,
         ),
@@ -101,8 +105,10 @@ fn dfg_2d_1_on_the_device() {
     solver.initialize(&mut field);
     let mask_cells = solver.mask().map_or(0, |m| m.fluid_cells());
     println!(
-        "  DFG 2D-1 ny {ny}: {nx}×{ny}×{nz} = {} cells ({mask_cells} fluid), h {h:.4e}, dt {dt:.3e}, t_end {t_end}",
-        g.cells()
+        "  DFG 2D-1 ny {ny}: {nx}×{ny}×{nz} = {} cells ({mask_cells} fluid), h {h:.4e}, dt {dt:.3e}, t_end {t_end}, centre x/h {:.3} y/h {:.3}",
+        g.cells(),
+        cx / h,
+        CY / h
     );
     let mut device = DeviceStep::new(solver, g);
     device.upload(&field);
@@ -138,8 +144,8 @@ fn dfg_2d_1_on_the_device() {
             let ci = |x: f64| ((x / h).round() as usize).clamp(2, nx - 2);
             let cj = |y: f64| ((y / h).round() as usize).clamp(2, ny - 2);
             let bx = (
-                ci(CX - margin),
-                ci(CX + margin),
+                ci(cx - margin),
+                ci(cx + margin),
                 cj(CY - 0.15),
                 cj(CY + 0.15),
                 0,
@@ -159,10 +165,10 @@ fn dfg_2d_1_on_the_device() {
             let (cd_s, cl_s) = (coef * fs.f[0], coef * fs.f[1]);
             let zc = 0.5 * lz;
             let p_front = mask
-                .pressure_at(&field.p, CX - 0.5 * D, CY, zc)
+                .pressure_at(&field.p, cx - 0.5 * D, CY, zc)
                 .unwrap_or(f64::NAN);
             let p_back = mask
-                .pressure_at(&field.p, CX + 0.5 * D, CY, zc)
+                .pressure_at(&field.p, cx + 0.5 * D, CY, zc)
                 .unwrap_or(f64::NAN);
             let dp = p_front - p_back;
             let (cd, cl, cd_cv, cl_cv) = (coef * fw[0], coef * fw[1], coef * fcv[0], coef * fcv[1]);