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API · /reynolds-api

Reynolds Number API

healthy 4,385 Subscribers

Dimensionless flow-number maths for fluid-mechanics similitude as an API, computed locally and deterministically. The reynolds endpoint computes the Reynolds number, Re = v·L/ν = ρvL/μ — the ratio of inertial to viscous forces — from the velocity, a characteristic length (pipe diameter) and either the kinematic viscosity or the density and dynamic viscosity, and classifies the flow as laminar (< 2300), transitional (2300–4000) or turbulent (> 4000). The froude endpoint computes the Froude number, Fr = v/√(g·L) — the ratio of inertia to gravity used for open-channel and ship flows — together with the critical velocity, and tells you whether the flow is subcritical (tranquil), critical or supercritical (shooting). The mach endpoint computes the Mach number, M = v/c, with the sound speed taken directly or worked out from the air temperature, c = √(γRT), and classifies the speed as subsonic, transonic, supersonic or hypersonic. Everything is computed locally and deterministically, so it is instant and private. Ideal for fluid-mechanics, aerodynamics and hydraulics tools, model-scaling and wind-tunnel similitude, pipe-flow and open-channel analysis, and engineering education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is dimensionless-number similitude; for pipe friction pressure drop use a Darcy-Weisbach API and for open-channel uniform flow use a Manning API.

#reynolds #froude #mach #fluid-mechanics #dimensionless #developer-tools
api.oanor.com/reynolds-api
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Machine-readable spec so AI agents can integrate this API.

/api/reynolds-api/openapi.json
/api/reynolds-api/llms.txt

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API health

healthy
Uptime
100.00%
Server probes · 24h
Avg latency
90 ms
Server probes · 24h
Subscribers
4,385
active
Total calls
32
last 7 days
status Full status page → · 24 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

Free

  • 2,000 calls / month
  • 2 requests / second
  • Hard cap (429 above quota, no overage)
  • Reynolds number for pipe & external flow
  • Single-call evaluation
  • SI units only
  • Community support
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Starter

€8.00 /month

  • 30,000 calls / month
  • 5 requests / second
  • Hard cap (429 above quota, no overage)
  • Reynolds, Froude & Mach endpoints
  • Laminar/transitional/turbulent regime flag
  • SI + imperial units
  • Email support
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Pro

€22.00 /month

  • 150,000 calls / month
  • 15 requests / second
  • Hard cap (429 above quota, no overage)
  • Full dimensionless-number suite
  • Batch similitude calculations
  • Critical-Reynolds threshold tuning
  • Priority support
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Mega

€69.00 /month

  • 767,000 calls / month
  • 40 requests / second
  • Hard cap (429 above quota, no overage)
  • Unlimited batch flow-number arrays
  • Highest throughput for CFD pre-processing
  • Dynamic-similarity scaling helpers
  • SLA-backed support
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Related APIs

Other APIs with overlapping tags.

Flow Rate API

Pipe-flow maths as an API, computed locally and deterministically. The flow endpoint relates the three quantities of pipe flow — volumetric flow rate, fluid velocity and pipe diameter — through the continuity relation Q = A·v (with A = π/4·D²): give any two and it returns the third, with the flow rate expressed in litres per second and minute, cubic metres per hour, US gallons per minute and cubic feet per minute, plus the velocity and the pipe cross-section. The reynolds endpoint computes the Reynolds number from velocity, diameter and the fluid (water, air, oil and more, or a custom kinematic viscosity) and classifies the flow as laminar, transitional or turbulent. The convert endpoint converts a flow rate between litres per second and minute, cubic metres per hour, US gallons per minute, cubic feet per minute and per second. Everything is computed locally and deterministically, so it is instant and private. It is computed in SI internally; Reynolds uses the kinematic viscosity at about 20°C. Ideal for plumbing and HVAC tools, pump and irrigation sizing, process and fluid-engineering software, and hydraulics calculators. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is fluid flow in pipes; for plain volume or unit conversion use a unit-conversion API.

api.oanor.com/flowrate-api

Isentropic Flow API

Isentropic compressible-flow (gas-dynamics) maths as an API, computed locally and deterministically. The isentropic endpoint gives the stagnation-to-static ratios of a perfect gas from a Mach number and the heat-capacity ratio γ (1.4 for air): the temperature ratio T0/T = 1 + (γ−1)/2·M², the pressure ratio p0/p = (T0/T)^(γ/(γ−1)), the density ratio and the area ratio A/A* relative to the sonic throat, and classifies the flow as subsonic, sonic or supersonic. The stagnation endpoint turns a static temperature and pressure plus a Mach number into the stagnation (total) conditions, the speed of sound a = √(γRT) and the flow velocity. The mach endpoint inverts the relations, solving the Mach number from a pressure, temperature or area ratio — an area ratio gives both the subsonic and supersonic roots — or from a velocity and temperature. Everything is computed locally and deterministically, so it is instant and private. Ideal for aerospace, propulsion, nozzle-design and wind-tunnel app developers, supersonic-flow and ducting tools, and engineering education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is compressible isentropic flow; for the standard atmosphere use an atmosphere API and for incompressible Bernoulli flow a Bernoulli API.

api.oanor.com/isentropic-api

Viscosity API

Fluid-viscosity physics as an API, computed locally and deterministically. The sutherland endpoint gives the dynamic viscosity of a gas at any temperature from Sutherland’s law, μ(T) = μ_ref·(T/T_ref)^1.5·(T_ref+S)/(T+S), with built-in constants for air, nitrogen, oxygen, carbon dioxide, hydrogen, helium and argon (or your own μ_ref, T_ref and S) — air comes out at about 1.72×10⁻⁵ Pa·s at 0 °C, 1.84×10⁻⁵ at 25 °C and 2.17×10⁻⁵ at 100 °C, returned in Pa·s, micro-Pa·s and centipoise. The kinematic endpoint converts between dynamic viscosity μ and kinematic viscosity ν through the density, ν = μ/ρ and μ = ν·ρ, so water at 1.002 cP and 998 kg/m³ becomes about 1.004 cSt. The convert endpoint handles viscosity units both ways — dynamic between Pa·s, centipoise and poise (1 Pa·s = 1000 cP = 10 P) and kinematic between m²/s, centistokes and stokes (1 m²/s = 10⁶ cSt = 10⁴ St). Temperatures are in °C or kelvin. Everything is computed locally and deterministically, so it is instant and private. Ideal for fluid-mechanics, CFD, process-engineering, lubrication, HVAC and chemical-engineering app developers, viscosity-correlation and unit-conversion tools, and simulation software. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This computes viscosity; for the Reynolds number that uses it use a Reynolds API.

api.oanor.com/viscosity-api

Particle Settling API

Particle settling-velocity maths as an API, computed locally and deterministically. The stokes endpoint computes the terminal settling velocity of a small spherical particle by Stokes' law, vt = (ρp − ρf)·g·d²/(18·μ), from the particle diameter and density, the fluid density and the dynamic viscosity, and checks the particle Reynolds number to tell you whether the creeping-flow assumption (Re < 1) still holds — a negative velocity means a buoyant particle that rises. The terminal endpoint computes the drag-based terminal velocity for larger, faster particles, vt = √(4·g·d·(ρp − ρf)/(3·Cd·ρf)), from a drag coefficient (≈0.44 in the turbulent Newton regime). The time endpoint computes the time for a particle to settle through a given depth, t = height/vt, taking the velocity directly or deriving it from the particle properties via Stokes. Everything is computed locally and deterministically, so it is instant and private. Ideal for water- and wastewater-treatment, mineral-processing and environmental-engineering tools, clarifier and settling-tank design, sediment and aerosol analysis, and engineering education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is particle sedimentation; for pipe-flow Reynolds/Froude/Mach numbers use a Reynolds API.

api.oanor.com/settling-api

Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for Reynolds Number API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Reynolds Number API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for Reynolds Number API?
Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.
How much does Reynolds Number API cost?
Reynolds Number API has a free tier with 100 calls / month. Paid plans start at €8.00 / month with higher quotas and faster rate limits.
Can I cancel my subscription anytime?
Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.
Is Reynolds Number API GDPR-compliant?
All requests to Reynolds Number API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.

Pick an endpoint from the list on the left to see its details and try it.

Code snippets

Sign up to get an API key, then call any path under your slug.

curl https://api.oanor.com/reynolds-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."
const res = await fetch("https://api.oanor.com/reynolds-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();
$ch = curl_init("https://api.oanor.com/reynolds-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);
import requests
r = requests.get(
    "https://api.oanor.com/reynolds-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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