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);
+}