CelerisLab/docs/validation/duetsch_re100_kc5_protocol.md

Prescribed in-line oscillation: Dütsch Re 100 / KC 5 — PROTOCOL DRAFT (not frozen)

Production under test: claude/moving-bodies-s3a at 653fd997 (unchanged). Primary source: Dütsch, Durst, Becker & Lienhart, J. Fluid Mech. 360, 249–271 (1998), doi:10.1017/S002211209800860X. Items marked ⟨verify⟩ must be taken from the paper itself before freezing; nothing here is read from plots. All numbers marked PROVISIONAL (ladder, window, domain, boundaries) are my choices and stay non-normative until the primary-spec packet and Astra's feasibility check land.

Criteria (kept separate)

• Same-grid frame consistency (G4, frozen 2%): already evaluated; not reused here.
• Cross-resolution criterion: every reported observable's error against the reference, and the fine-pair difference, must decrease monotonically over the resolution ladder. No numeric grid threshold and no order label is added.
• Reference agreement: only against values with provenance (section 6), with an observable-specific error/uncertainty criterion declared per observable before runs (OPEN). Monotone decrease alone is not a literature pass.
• Duration/periodicity gate (section 1a) must pass before any statistic is collected.

1. Kinematics

• In-line only: x(t) = -A sin(2 pi t / T), u(t) = -U_max cos(2 pi t / T) ⟨verify sign and phase origin⟩; KC = U_max T / D = 2 pi A / D = 5, Re = U_max D / nu = 100, so A = 5 D / (2 pi).
• Prescribed per step through set_body(offset, vx) + run(1), offset and velocity evaluated analytically at step n (no differencing).
• Start: the paper's motion from rest ⟨verify Dütsch start⟩. A one-cycle smooth ramp is a separately named variant that only checks start independence.
• Phase convention: the motion uses the analytic offset/velocity at the step's time level n; the per-step force (run(1), read_force(normalize=True)) is attributed to the same n. Whether the paper's phases refer to endpoint values or interval averages is ⟨verify⟩; comparisons state which.

1a. Duration and periodic-state gate (auditable, every case)

• Recorded per case: dx, dt, D, U_max, nu (lattice and nondimensional), steps per period, total steps, total nondimensional duration t U_max / D and in periods, number of discarded cycles, accepted cycle window.
• Every case in a comparison uses the SAME accepted window in periods (finer grids run proportionately more native steps for the same physical time).
• Periodic-state adequacy is demonstrated, not assumed: per-cycle mean and RMS of Fx and the Morison fit per cycle must change by less than a predeclared cycle-to-cycle tolerance (OPEN) over the last cycles before the window; otherwise the run is extended and the window moved by whole periods, and the failure is recorded. Cycles 4–6 is PROVISIONAL only.
• The G4 timing check (100 coarse vs 400 diffusive-fine steps) is a matched short transient, not evidence of periodic convergence.

2. Resolution ladder (uniform only, fixed Mach)

D (cells)	U_max	nu_lat	tau	steps / period
20	.04	.008	.524	2,500
40	.04	.016	.548	5,000
80	.04	.032	.596	10,000

• MRT collision (SRT at tau ≈ .524 is the recorded unstable regime).
• Mach check: U_max .02 vs .04 at D = 40 (separate, labelled).

3. Domain and boundaries

• Square still-fluid box; size PROVISIONAL (e.g. 20 D vs 40 D check at D = 40) ⟨verify Dütsch domain extent⟩; no generic size is normative.
• Boundary family declared by the runner owner before running (x-periodic / y free-slip or closed walls, whatever the dense runner supports without production change); swept band ±A + R + 2 clear of any seam.
• Per-step displacement ≤ .04 cells (bound .5).

4. Observables (raw, per step, preserved)

• obs Fx, Fy (CME) and the diagnostics columns (MovingTables.DIAG): CME, CME + Wen, CME + cover − uncover reported separately; crossings, eq_only, no_donor.
• Velocity u, v on lines at the paper's x-stations relative to the mean cylinder position and at its phase angles ⟨verify stations and phases⟩; cell-centred values, documented bilinear interpolation in physical units.

5. Metrics

• Morison C_D, C_M by least squares over the measured cycles with the paper's force definition and sign ⟨verify formula⟩; per-cycle RMS force; force phase history; phase-resolved velocity profiles.
• Unit map for each candidate stated with k = rho dx^3 / dt^2 per span.

6. Reference data provenance

• Reference types kept separate: (a) phase-averaged LDA velocity measurements; (b) the paper's computed results, including forces and Morison fits — a computed reference, not a measured force. The paper itself reports the Morison-fit error as larger than its coarse grid/time numerical error, so C_D, C_M agreement is judged against that stated fit uncertainty.
• Accepted: values from the paper's tables, or digitized figure curves with figure number, tool and uncertainty recorded. Curves without provenance are qualitative only. Values quoted by later papers are secondary until checked.
• No cost estimate is normative; Astra's smoke run measures it.

7. Order

Protocol review → test driver (no production change) → runs → physical validation verdict → only then single-cylinder VIV. No AMR, no pinball.