CALCULATORS / UNITS AND DIMENSIONAL REASONING

Reynolds number calculator for dimensional similarity

Reynolds similarity example; incompressible Newtonian flow.

units-dimensionless-groups.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	reynolds
	1000
	800

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

laminar example1000.00 ✓ passes

BASELINE INPUTS

density1000 kg/m^3velocity0.1 m/sdiameter0.01 mviscosity0.001 Pa*s

CALCULATED

reynolds1000

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Dimensional-analysis groups
# Scope: Reynolds similarity example; incompressible Newtonian flow.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

density = 1000 kg/m^3
velocity = 0.1 m/s
diameter = 0.01 m
viscosity = 0.001 Pa*s

reynolds := density*velocity*diameter/viscosity

check laminar example: reynolds < 2300

scenario alternative: density = 800 kg/m^3

Calculated from your source · not saved

Baseline · Baseline

laminar example1000.00 ✓ passes

alternative · alternative

laminar example800.00 ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

reynolds: reynolds = density*velocity*diameter/viscosity

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

density: 1000 kg/m^3
velocity: 0.1 m/s
diameter: 0.01 m
viscosity: 0.001 Pa*s

Calculated

reynolds: 1000

Assumptions and limits

Reynolds similarity example; incompressible Newtonian flow.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Dimensional-analysis groups. Inputs: variables; dimensions; selected phenomenon. Outputs: dimensionless groups; missing variables. Model scope: Dimensional analysis and explicit reference conventions. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: variables, dimensions, selected phenomenon
Outputs: dimensionless groups, missing variables
Modes: convert, solve-for
Drawing: Quantity diagram

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS