NSCBC 2/7: transverse terms in the modelled incoming wave - #1059
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This was referenced Aug 28, 2026
…LODI limit The base characteristic treatment as a ghost-cell fill: one wave decomposition in an outward-normal frame, two boundary types. Outgoing invariants extrapolate from the interior on a minmod-limited slope; the incoming acoustic is modelled as a Poinsot-Lele relaxation written as a gradient increment (a mesh-independent rate, so literature coefficients transfer), sigma at outflows, relax_u/relax_t at inflows, with a stateless feed-forward slot (Target::dudt) for problems that inject signals. Supersonic faces are exact. Flow reversal at an outflow runs the same closure with the material slopes upwinded off across a narrow Mach band -- one code path on both sides of u_out = 0. The fill is a pure function of pre-launch interior data: idempotent, order-independent, bit-reproducible across restarts and decompositions, GPU-resident (POD captures, counted fallbacks instead of device aborts). Every fallback increments a counter and the counters report by default -- a silent fallback is indistinguishable from a healthy boundary. Problems opt in per boundary POINT through a bcnormal_nscbc() hook returning a Target; a face may mix inflow, outflow and wall. EB requires eb_zero_body_state (fatal otherwise, the fill detects covered cells by non-positive density); an AMR fine face touching a characteristic boundary warns. This PR is the 1-D-normal LODI limit on purpose: transverse terms and the reacting-boundary closures arrive as the next two PRs in this stack, each an additive, default-off correction to the modelled incoming wave (some comments here forward-reference them). Verification driver and regression cases follow in the stack; headline number from the case PR: an acoustic pulse leaves through this boundary with 0.8% reflection against 97% for a hard-pressure fill. Also removes the dead nscbc_adv/nscbc_diff keys of the deleted Fortran implementation (aborting, not ignoring, when an inputs file still sets them) and retires the 1 K default for eb_boundary_T in favour of 300 K. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XU8M23nucKsu1do2WxXFeq
The multi-dimensional correction: -(1 - beta) T_in on the incoming amplitude, where T_in carries the tangential convective and dilatational terms in the outward frame (the ghost-cell transplantation of Motheau's T1/T4 -- one expression for lo and hi faces). Tangential derivatives come from the boundary cell's clamped neighbours; at a corner the stencil collapses one-sided or to nothing, which is the measured replacement for the AIAA corner-coupling machinery. The beta blend is exact for a plane wave at incidence theta: beta_opt = 1 - cos(theta)/(1 + cos(theta)) -- 0.5 head-on, toward 1 at grazing -- and both measured optima in the COVO/pulse suite land on it. The response is asymmetric (a wrong beta is worse than an absent one), so the default stays 1: this PR is bit-inert until a problem opts in, and every result of the previous PR is unchanged. The clamp leaves a small measured seam residual where a characteristic face meets a periodic direction, and that trade is guarded rather than assumed: nscbc_check_periodic_wrap() measures the ghost-image mismatch at startup, reports it beside the boundary-row spread (so a vacuous pass is visible), and aborts above 1e-2 -- an order above the worst known-good measurement and an order below what a broken stencil produces. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XU8M23nucKsu1do2WxXFeq
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Stacked on #1058 (part 2/7 of the stack tracked in #1057). The reviewable content of this PR is its LAST commit — the earlier commits are the lower stack levels and will vanish from this diff as they merge and the stack rebases.
The multi-dimensional correction: -(1 - beta) T_in on the incoming
amplitude, where T_in carries the tangential convective and dilatational
terms in the outward frame (the ghost-cell transplantation of Motheau's
T1/T4 -- one expression for lo and hi faces). Tangential derivatives
come from the boundary cell's clamped neighbours; at a corner the
stencil collapses one-sided or to nothing, which is the measured
replacement for the AIAA corner-coupling machinery.
The beta blend is exact for a plane wave at incidence theta:
beta_opt = 1 - cos(theta)/(1 + cos(theta)) -- 0.5 head-on, toward 1 at
grazing -- and both measured optima in the COVO/pulse suite land on it.
The response is asymmetric (a wrong beta is worse than an absent one),
so the default stays 1: this PR is bit-inert until a problem opts in,
and every result of the previous PR is unchanged.
The clamp leaves a small measured seam residual where a characteristic
face meets a periodic direction, and that trade is guarded rather than
assumed: nscbc_check_periodic_wrap() measures the ghost-image mismatch
at startup, reports it beside the boundary-row spread (so a vacuous
pass is visible), and aborts above 1e-2 -- an order above the worst
known-good measurement and an order below what a broken stencil
produces.
🤖 Generated with Claude Code
https://claude.ai/code/session_01XU8M23nucKsu1do2WxXFeq