Source: https://guthlabs.ai/docs/instruments/reynolds-number-calculator/mechanism/

instrument mechanism / verified-clean

# Reynolds Number Calculator mechanism

The inspectable method record for Reynolds Number Calculator, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## 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

[01**Overview**](<https://guthlabs.ai/docs/instruments/reynolds-number-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/reynolds-number-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/reynolds-number-calculator/qualification/>)

## 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`