embedded3: cut predictor convection carries ρ (host + e3_cut.cu; density-scaling pin); operator load route includes the wall exchange (exchange.rs); reconstructed_parts, probe aperture floor knob; dfg_split diagnostic test

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

crates/specialized/rtx-cfd/tests/embedded3_density_scaling.rs

@@ -0,0 +1,101 @@
+//! Density-scaling pin for the cut-cell predictor (host): the same flow at
+//! `ρ` and `1000 ρ` with `μ` scaled alike is the same velocity field and a
+//! pressure scaled by 1000 — every term of the momentum equation carries
+//! `ρ` (the convection term used to be a bare volume flux times velocity,
+//! which starved every ρ = 1000 cut-cell run of convection).
+use rtx_cfd::solvers::incompressible::ConvectionScheme;
+use rtx_cfd::solvers::incompressible::embedded3::{
+    Body, Boundaries, Field, Fluid, Grid, Parameters, Side, Solver, WallScheme,
+};
+
+fn run(rho: f64, moving: bool) -> Field {
+    let n = 16;
+    let h = 1.0 / n as f64;
+    let g = Grid::cubic(2 * n, n, n, h);
+    let nu = 1e-2;
+    let mut solver = Solver::new(
+        Fluid {
+            density: rho,
+            viscosity: rho * nu,
+            reference_velocity: 1.0,
+            reference_length: 0.3,
+        },
+        Parameters {
+            corrector_steps: 2,
+            tolerance: 1e-11,
+            convection_scheme: ConvectionScheme::TvdVanAlbada,
+            wall_scheme: WallScheme::CutCell,
+            boundaries: Boundaries {
+                x1: Side::PressureOutlet,
+                ..Boundaries::default()
+            },
+            max_surface_speed: if moving { Some(0.5) } else { None },
+            ..Parameters::default()
+        },
+    );
+    solver.set_boundary_velocity(|x, _, _, _| {
+        if x <= 0.0 {
+            (1.0, 0.0, 0.0)
+        } else {
+            (0.0, 0.0, 0.0)
+        }
+    });
+    let xc = move |t: f64| 0.7 + if moving { 0.1 * (3.0 * t).sin() } else { 0.0 };
+    let body = Body::from_sdf(move |x, y, z, t| {
+        ((x - xc(t)).powi(2) + (y - 0.5_f64).powi(2) + (z - 0.5_f64).powi(2)).sqrt() - 0.15
+    })
+    .with_surface_velocity(move |_, _, _, t| {
+        (if moving { 0.3 * (3.0 * t).cos() } else { 0.0 }, 0.0, 0.0)
+    });
+    if moving {
+        solver.set_moving_body(body);
+    } else {
+        solver.set_body(body);
+    }
+    let mut field = Field::new(g);
+    for k in 0..n {
+        for j in 0..n {
+            for i in 0..=2 * n {
+                field.u[g.uface(k, j, i)] = 1.0;
+            }
+        }
+    }
+    solver.initialize(&mut field);
+    let dt = 0.2 * h;
+    for _ in 0..40 {
+        solver.advance(&mut field, dt);
+    }
+    field
+}
+
+fn compare(moving: bool) {
+    let a = run(1.0, moving);
+    let b = run(1000.0, moving);
+    let max = |x: &[f64], y: &[f64], s: f64| {
+        x.iter()
+            .zip(y)
+            .map(|(p, q)| (p - q / s).abs())
+            .fold(0.0, f64::max)
+    };
+    let du = max(&a.u, &b.u, 1.0)
+        .max(max(&a.v, &b.v, 1.0))
+        .max(max(&a.w, &b.w, 1.0));
+    let dp = max(&a.p, &b.p, 1000.0);
+    let pscale = a.p.iter().fold(0.0f64, |m, p| m.max(p.abs()));
+    println!("  moving {moving}: max |Δu| {du:.3e}, max |Δp/1000| {dp:.3e} (p scale {pscale:.3e})");
+    assert!(du < 1e-9, "velocity is not density-invariant: {du:.3e}");
+    assert!(
+        dp < 1e-9 * pscale.max(1.0),
+        "pressure does not scale with density: {dp:.3e}"
+    );
+}
+
+#[test]
+fn cut_cell_flow_is_density_invariant_at_rest() {
+    compare(false);
+}
+
+#[test]
+fn cut_cell_flow_is_density_invariant_moving() {
+    compare(true);
+}

crates/specialized/rtx-cfd/tests/embedded3_dfg_2z.rs

@@ -201,6 +201,23 @@ fn dfg_3d_2z_on_the_device() {
         println!("  instant written to {}", path.display());
     }
     let (cd, cl, cd_cv, cl_cv, dp) = last.expect("samples");
+    {
+        // S2-1 diagnosis: each wall route split into its pressure and shear parts.
+        let body = solver.body().expect("body");
+        let (po, so) = mask
+            .cut_wall_force_parts(body, &field, RHO * NU, solver.time())
+            .expect("parts");
+        let (pr, sr) = mask
+            .cut_wall_force_reconstructed_parts(body, &field, RHO * NU, solver.time(), None)
+            .expect("parts");
+        println!(
+            "  SPLIT ny {ny}: operator c_D pressure {:.4} + shear {:.4}; reconstructed pressure {:.4} + shear {:.4}",
+            coef * po[0],
+            coef * so[0],
+            coef * pr[0],
+            coef * sr[0]
+        );
+    }
     println!(
         "  FINAL ny {ny}: c_D {cd:.4} (CV {cd_cv:.4}, routes {:.2e} apart; reconstructed {:.4}, {:.2e} from CV)  c_L {cl:.5} (CV {cl_cv:.5}, reconstructed {:.5})  Δp {dp:.4}  — reference c_D 6.05–6.25, c_L 0.008–0.010, Δp 0.165–0.175; {:.0} s",
         ((cd - cd_cv) / cd).abs(),

crates/specialized/rtx-cfd/tests/embedded3_dfg_split.rs

@@ -0,0 +1,130 @@
+//! S2-1 diagnosis (host): DFG 3D-2Z at a coarse rung with every load
+//! route split into pressure and shear parts — which part of the wall
+//! routes departs from the box route. `RTX_E3_DFG_NY` (default 31).
+use rtx_cfd::solvers::incompressible::ConvectionScheme;
+use rtx_cfd::solvers::incompressible::embedded3::{
+    Body, Boundaries, Field, Fluid, Grid, Parameters, Side, Solver, WallScheme,
+};
+
+const H: f64 = 0.41;
+const L: f64 = 2.5;
+const D: f64 = 0.1;
+const CX: f64 = 0.5;
+const CY: f64 = 0.2;
+const U_M: f64 = 0.45;
+const U_BAR: f64 = 4.0 / 9.0 * U_M;
+const RHO: f64 = 1.0;
+const NU: f64 = 1e-3;
+
+fn inflow(y: f64, z: f64) -> f64 {
+    16.0 * U_M * y * z * (H - y) * (H - z) / (H * H * H * H)
+}
+
+#[test]
+#[ignore = "host DFG at ny 31 with the routes split (about half an hour)"]
+fn dfg_routes_split_on_the_host() {
+    let ny: usize = std::env::var("RTX_E3_DFG_NY")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(31);
+    let h = H / ny as f64;
+    let nx = (L / h).round() as usize;
+    let nz = ny;
+    let dt = (0.3 * h / U_M).min(0.5 * h * h / (6.0 * NU));
+    let mut solver = Solver::new(
+        Fluid {
+            density: RHO,
+            viscosity: RHO * NU,
+            reference_velocity: U_BAR,
+            reference_length: D,
+        },
+        Parameters {
+            corrector_steps: 2,
+            tolerance: 1e-8,
+            convection_scheme: ConvectionScheme::TvdVanAlbada,
+            wall_scheme: WallScheme::CutCell,
+            boundaries: Boundaries {
+                x1: Side::PressureOutlet,
+                ..Boundaries::default()
+            },
+            ..Parameters::default()
+        },
+    );
+    solver.set_boundary_velocity(|x, y, z, _t| {
+        if x <= 0.0 {
+            (inflow(y, z), 0.0, 0.0)
+        } else {
+            (0.0, 0.0, 0.0)
+        }
+    });
+    solver.set_body(Body::extruded(
+        rtx_cfd::solvers::incompressible::EmbeddedBody::circle(CX, CY, 0.5 * D),
+        H,
+    ));
+    let g = Grid::cubic(nx, ny, nz, h);
+    let mut field = Field::new(g);
+    for k in 0..nz {
+        for j in 0..ny {
+            let u0 = inflow((j as f64 + 0.5) * h, (k as f64 + 0.5) * h);
+            for i in 0..=nx {
+                field.u[g.uface(k, j, i)] = u0;
+            }
+        }
+    }
+    solver.initialize(&mut field);
+    let coef = 2.0 / (RHO * U_BAR * U_BAR * D * H);
+    let steps = (8.0 / dt).ceil() as usize;
+    let start = std::time::Instant::now();
+    let mut last = (0.0, 0.0);
+    for step in 0..steps {
+        let r = solver.advance(&mut field, dt);
+        if (step + 1) % (steps / 20).max(1) == 0 || step + 1 == steps {
+            let t = solver.time();
+            let mask = solver.mask().unwrap();
+            let body = solver.body().unwrap();
+            let mu = RHO * NU;
+            let (po, so) = mask.cut_wall_force_parts(body, &field, mu, t).unwrap();
+            let ex = mask
+                .cut_wall_exchange_force(body, &field, mu, RHO, t, None)
+                .unwrap();
+            let (pr, sr) = mask
+                .cut_wall_force_reconstructed_parts(body, &field, mu, t, None)
+                .unwrap();
+            let margin = 3.0 * D;
+            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),
+                cj(CY - 0.15),
+                cj(CY + 0.15),
+                0,
+                nz,
+            );
+            let fcv = mask.control_volume_force_with_walls(&field, dt, RHO, mu, None, bx, true);
+            let cd = |f: [f64; 3]| coef * f[0];
+            println!(
+                "  t {t:7.3}: c_D operator {:.4} (p {:.4} + s {:.4} + exchange {:.4}) | reconstructed {:.4} (p {:.4} + s {:.4}) | box {:.4}; residual {:.1e} [{:.0} s]",
+                cd(po) + cd(so) + cd(ex),
+                cd(po),
+                cd(so),
+                cd(ex),
+                cd(pr) + cd(sr),
+                cd(pr),
+                cd(sr),
+                cd(fcv),
+                r.final_residual,
+                start.elapsed().as_secs_f64()
+            );
+            let now = (cd(po) + cd(so) + cd(ex), cd(fcv));
+            if (now.0 - last.0).abs() < 1e-4 * now.0.abs()
+                && (now.1 - last.1).abs() < 1e-4 * now.1.abs()
+                && t > 2.0
+            {
+                println!("  settled");
+                break;
+            }
+            last = now;
+        }
+    }
+}