Fix temperature drift caused by ekh timing mismatch in flux-type top BC#318
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Xinzhe20 wants to merge 1 commit into
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Fix temperature drift caused by ekh timing mismatch in flux-type top BC#318Xinzhe20 wants to merge 1 commit into
Xinzhe20 wants to merge 1 commit into
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closure() updates ekh to ekh_{N+1} at the start of each RK3 substep,
but fluxtop() (called via boundary()) had already set the top ghost
cell thl0(ke+1) using the previous ekh_N. diffc() then computed the
top-boundary flux using the mismatched ekh_{N+1}, causing the
realized flux to deviate from the prescribed wttop by ~0.72%,
producing a systematic linear domain-temperature drift (dT/dt not
converging to zero, scaling with dt).
Fix: call fluxtop() again immediately after closure() inside
subgrid(), using the just-updated ekh, before diffc() consumes the
ghost cell. Only active when ltempeq .and. BCtopT == BCtopT_flux.
Verified on Imperial CX3: drift reduced from +7.93e-04 K.m/s to
-2.10e-05 K.m/s (97% reduction), case 001 (unpatched) vs case 002
(patched), bctfz = wttop = -0.1. Re-verified with a clean rebuild
(case 005, 26000s run) to confirm the cleaned-up patch reproduces
identical convergence behavior.
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closure() updates ekh to ekh_{N+1} at the start of each RK3 substep, but fluxtop() (called via boundary()) had already set the top ghost cell thl0(ke+1) using the previous ekh_N. diffc() then computed the top-boundary flux using the mismatched ekh_{N+1}, causing the realized flux to deviate from the prescribed wttop by ~0.72%, producing a systematic linear domain-temperature drift (dT/dt not converging to zero, scaling with dt).
Fix: call fluxtop() again immediately after closure() inside subgrid(), using the just-updated ekh, before diffc() consumes the ghost cell. Only active when ltempeq .and. BCtopT == BCtopT_flux.
Verified on hpc: drift reduced from +7.93e-04 K.m/s to -2.10e-05 K.m/s (97% reduction), case 001 (unpatched) vs case 002 (patched), bctfz = wttop = -0.1. Re-verified with a clean rebuild (case 005, 26000s run) to confirm the cleaned-up patch reproduces identical convergence behavior.
Closes #317