Source: https://guthlabs.ai/docs/instruments/sphere-cylinder-drag-coefficient-vs-reynolds-correlation/mechanism/

instrument mechanism / verified-clean

# Sphere/Cylinder Drag Coefficient vs Reynolds Correlation mechanism

The inspectable method record for Sphere/Cylinder Drag Coefficient vs Reynolds Correlation, kept separate from implementation and qualification.

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

## Model scope

The four vectors use explicit standard conventions and are independently hand-computable. The two low-Re sphere vectors exactly reproduce the widely memorized Stokes values Cd=240 at Re=0.1 and Cd=24 at Re=1. The specification needs an authoritative table or explicit correlation, interpolation rule, valid ranges, cylinder geometry/orientation inputs, and a defined Cd reference area before it can receive PASS.

- The specification does not define the actual piecewise equations, drag-curve table coordinates, interpolation method, or extrapolation behavior; therefore 'standard drag curve elsewhere' is not uniquely computable.

- Cd=24/Re is the Stokes-law result for a sphere in creeping flow and should not be presented as a general low-Re formula for cylinders.

- Cylinder drag requires at least orientation, aspect ratio, end effects, surface roughness, blockage ratio, and flow regime; 'cylinder' alone is insufficient. The cylinder test below assumes an infinite circular cylinder in crossflow.

- A single ±10-20% accuracy label is not uniformly honest: uncertainty can be substantially larger near the sphere drag crisis, cylinder transition regions, and when geometry or turbulence conditions are unspecified.

- The Reynolds-number definition and characteristic length are omitted. For these correlations, Re must normally be based on sphere diameter or cylinder diameter.

## Units and conventions

- Re is dimensionless and is computed as Re=rho*v*D/mu, using mutually consistent units for density, velocity, diameter, and dynamic viscosity.

- For the sphere vectors, D is the sphere diameter and Cd uses projected frontal area pi*D^2/4.

- For the cylinder vector, D is cylinder diameter, the cylinder is circular and effectively infinite in span, and the flow is normal to its axis; Cd uses projected area D times span.

- The tabulated values are empirical textbook values under standard incompressible, single-body, low-blockage conditions; compressibility, wall effects, and free-surface effects are excluded.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "Re": 0.1,
    "shape": "sphere"
  },
  "expected_outputs": {
    "Cd": 240
  },
  "reference_data": {
    "drag_relation": {
      "value": "Cd=24/Re",
      "source_convention": "widely tabulated standard value: Stokes drag law for a sphere"
    },
    "validity_range": {
      "value": "Re much less than 1",
      "source_convention": "widely tabulated standard value: creeping-flow sphere regime"
    }
  },
  "working": "Use the Stokes sphere relation: Cd=24/Re. Substitute Re=0.1: Cd=24/0.1=240. Therefore Cd=240.0."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

Re=0 produces division by zero and must be rejected or reported undefined. The exact value at Re=1 and all higher-Re outputs are also under-specified unless the instrument supplies a definite drag-curve table or fit; the representative higher-Re calculation is therefore only a reference check.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/sphere-cylinder-drag-coefficient-vs-reynolds-correlation/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/sphere-cylinder-drag-coefficient-vs-reynolds-correlation/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/sphere-cylinder-drag-coefficient-vs-reynolds-correlation/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-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`