embedded3 S2-5: the cut wall sat ½(1−α)h inside the body — cross diffusion over the open-part centroid spacing (RTX_E3_DIFFUSION_CENTROID; host + e3_cut.cu, shift tables, point-implicit excess); flat-wall effective-position instrument; DFG 2D-1 ladder tests (device + host); knobs tried and refuted along the way (oblique distance, axis exchange, centroid pressure gradient)

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

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/wall.rs

@@ -99,6 +99,17 @@ pub struct Mask {
     pub(super) density: f64,
     /// The cut wall's shear closure order (S2-4).
     pub(super) wall_order: u8,
+    /// The oblique wall distance of the cut faces (S2-5).
+    pub(super) wall_distance_oblique: bool,
+    /// The axis-distance implicit wall exchange (S2-5).
+    pub(super) wall_exchange_axis: bool,
+    /// The centroid prototype's pressure-gradient weights per u / v / w face.
+    /// The centroid-distance cross diffusion (S2-5).
+    pub(super) diffusion_centroid: bool,
+    /// The open-part centroid shifts per u / v / w face, three components
+    /// interleaved (built with `diffusion_centroid`).
+    pub(super) face_shifts: Option<[Vec<f64>; 3]>,
+    pub(super) grad_weights: Option<(Vec<f64>, Vec<f64>, Vec<f64>)>,
 }
 
 /// The z lattice position of a query: the lower plane index, the upper
@@ -512,6 +523,11 @@ impl Mask {
             scheme: crate::solvers::incompressible::ConvectionScheme::Upwind,
             density: 1.0,
             wall_order: 1,
+            wall_distance_oblique: false,
+            wall_exchange_axis: false,
+            grad_weights: None,
+            diffusion_centroid: false,
+            face_shifts: None,
         })
     }
 
@@ -616,6 +632,15 @@ impl Mask {
     /// Fluid volume fraction of a cell (1 on the binary wall).
     #[inline]
     #[must_use]
+    pub fn grad_weight(&self, c: usize, idx: usize) -> f64 {
+        self.grad_weights.as_ref().map_or(1.0, |w| match c {
+            0 => w.0[idx],
+            1 => w.1[idx],
+            _ => w.2[idx],
+        })
+    }
+    #[inline]
+    #[must_use]
     pub fn vol(&self, idx: usize) -> f64 {
         self.cut.as_ref().map_or(1.0, |c| c.vol[idx])
     }