Reynolds Number Calculator mechanism

Model scope

The Reynolds-number formula is correct, but the instrument is not ready for an unqualified internal-or-external flow classification. The empty honest_label should be replaced with a statement of the selected characteristic-length definition, unit requirements, geometry-specific thresholds, and the fact that transition boundaries are approximate. Verdict remains NEEDS_REVIEW until these choices are explicit.

• Re=ρVL/μ=VL/ν is the standard Reynolds-number formula when ρ, V, L, μ, and ν use mutually consistent units.
• The characteristic length L is underspecified: for internal flow it is commonly the pipe diameter, while for noncircular ducts it is commonly the hydraulic diameter; for external flow it depends on the geometry and stated reference length.
• Flow-regime thresholds are missing and are not universal. The commonly used internal smooth circular-pipe thresholds Re<2300 laminar, 2300≤Re≤4000 transitional, and Re>4000 turbulent do not generally apply to external flow.
• The declared plain-arithmetic engine can calculate Re but cannot by itself provide the requested categorical regime without comparison/branching logic.

Units and conventions

• Use SI-consistent units: ρ in kg/m³, V in m/s, L in m, μ in Pa·s (kg/(m·s)), and ν in m²/s.
• The two formulas are equivalent only when ν=μ/ρ.
• For the test vectors, L is the pipe diameter and the classification basis is a smooth circular internal pipe using Re<2300 laminar, 2300≤Re≤4000 transitional, and Re>4000 turbulent.
• External-flow classification requires the geometry, reference length, and an explicitly selected transition criterion.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "flow_type": "internal_smooth_circular_pipe",
    "rho_kg_m3": 998,
    "velocity_m_s": 2,
    "characteristic_length_m": 0.05,
    "mu_Pa_s": 0.001
  },
  "expected_outputs": {
    "Re": 99800,
    "flow_regime": "turbulent"
  },
  "working": "Re=ρVL/μ=(998 kg/m³)(2 m/s)(0.05 m)/(0.001 Pa·s)=99.8/0.001=99,800. Since Re>4000, the regime is turbulent."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The specification leaves internal versus external classification thresholds and negative-velocity convention unspecified, and μ = 0 produces an undefined result that must be rejected rather than numerically evaluated.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json