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 (Grok) before freezing; nothing here is read from plots.

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).

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⟩. Measured window: whole cycles 4–6, fixed now, never shortened afterwards. A one-cycle smooth ramp is a separately named variant that only checks start independence.

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, default 40 D; domain check 20 D vs 40 D at D = 40 ⟨verify Dütsch domain extent⟩.
• 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

• 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.

7. Order

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