NSCBC 3/7: reacting boundaries and fronts - #1060
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…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
What a flame does to a characteristic boundary, and the closures that survive it -- all default-off, so the previous two PRs' results are unchanged to the bit until a problem opts in. - The reaction source enters the modelled incoming wave with +(1 - beta_s) S_p (Sutherland-Kennedy): a flame in the boundary cells raises pressure at a rate the relaxation has no model for, and without the term the mean sits off target by S_p/K. The sign is PLUS -- the exact steady flame has dR_-/dn = +S_p/(rho c^2), and the driver PR carries a convention-free check of exactly that. S_p is the compositional dp/dt at fixed (rho, e): closed form for ideal gas, a directional finite difference along the reaction path for SRK. - extrap_temperature closes the lambda_0 family on temperature instead of the entropy invariant. The diffusion operator forms boundary-face fluxes from these ghosts, so the ghost dT/dn IS the heat flux leaving; the entropy closure overstates a flame-like face gradient by 40%. This is the flag that lets a flame survive the outflow. - extrap_material continues the material part of R_- into the ghost, bounded through the acoustically-blind entropy family (extrapolating R_-'s own gradient is positive feedback, measured 16x). For fronts that SIT on the boundary; a transit over-vents with it on. - backflow_material treats FIRM reversal as a local inflow of the Target's reservoir state, ramped over an outward-Mach band continuous with the reversal upwinding underneath -- without it a face in sustained recirculation feeds the domain its own exhaust. Also the structure advisory: material structure sitting in outflow boundary cells is counted, and the counter report prints the measured flame-on-boundary recipe when it fires. Measured guidance and the sitting/transit tables live with the regression cases later in this stack (NSCBC-FlameOutflow, README). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XU8M23nucKsu1do2WxXFeq
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Stacked on #1059 (part 3/7 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.
What a flame does to a characteristic boundary, and the closures that
survive it -- all default-off, so the previous two PRs' results are
unchanged to the bit until a problem opts in.
The reaction source enters the modelled incoming wave with
+(1 - beta_s) S_p (Sutherland-Kennedy): a flame in the boundary cells
raises pressure at a rate the relaxation has no model for, and
without the term the mean sits off target by S_p/K. The sign is PLUS
-- the exact steady flame has dR_-/dn = +S_p/(rho c^2), and the
driver PR carries a convention-free check of exactly that. S_p is
the compositional dp/dt at fixed (rho, e): closed form for ideal gas,
a directional finite difference along the reaction path for SRK.
extrap_temperature closes the lambda_0 family on temperature instead
of the entropy invariant. The diffusion operator forms boundary-face
fluxes from these ghosts, so the ghost dT/dn IS the heat flux
leaving; the entropy closure overstates a flame-like face gradient by
40%. This is the flag that lets a flame survive the outflow.
extrap_material continues the material part of R_- into the ghost,
bounded through the acoustically-blind entropy family (extrapolating
R_-'s own gradient is positive feedback, measured 16x). For fronts
that SIT on the boundary; a transit over-vents with it on.
backflow_material treats FIRM reversal as a local inflow of the
Target's reservoir state, ramped over an outward-Mach band
continuous with the reversal upwinding underneath -- without it a
face in sustained recirculation feeds the domain its own exhaust.
Also the structure advisory: material structure sitting in outflow
boundary cells is counted, and the counter report prints the measured
flame-on-boundary recipe when it fires. Measured guidance and the
sitting/transit tables live with the regression cases later in this
stack (NSCBC-FlameOutflow, README).
🤖 Generated with Claude Code
https://claude.ai/code/session_01XU8M23nucKsu1do2WxXFeq