Fluid Dynamics Calculator
Analyze pipe flow, losses, Reynolds number, pump curves, and fluid-system operating conditions with interactive visual results.
Pipe flow, pumps, and open channels
Four linked calculators cover the steady one-dimensional cases that come up most often in fluid-system work: internal pipe flow, pump sizing, open-channel hydraulics, and fluid property lookup. Pipe-flow results are shown alongside an animated visualization whose particles are advected by the actual velocity profile, so the difference between laminar and turbulent flow is visible rather than asserted.
- Reynolds number and flow-regime classification.
- Darcy friction factor, pressure drop, and head loss.
- Pump power, head, and NPSH.
- Froude number, hydraulic radius, and flow classification for open channels.
Equations used
The correlations are the standard steady-flow relationships:
- Reynolds number: Re = ρ·v·D / μ
- Darcy–Weisbach pressure drop: ΔP = f·(L/D)·(ρ·v²/2)
- Friction factor, laminar (Hagen–Poiseuille): f = 64 / Re
- Friction factor, turbulent smooth pipe (Blasius): f = 0.316 / Re^0.25
- Head loss: hL = ΔP / (ρ·g)
- Froude number: Fr = v / √(g·d)
Frequently asked questions
- What Reynolds number means laminar or turbulent flow?
- For flow in a circular pipe, Re below about 2300 is laminar, Re above about 4000 is turbulent, and the band between is transitional and unpredictable. Laminar flow moves in orderly parallel layers with a parabolic velocity profile; turbulent flow mixes across the pipe and has a much blunter profile with a thin steep layer at the wall.
- How do you calculate pressure drop in a pipe?
- Use the Darcy–Weisbach equation, ΔP = f·(L/D)·(ρ·v²/2), where f is the Darcy friction factor, L is the pipe length, D the internal diameter, ρ the fluid density, and v the mean velocity. The friction factor depends on the Reynolds number and the relative roughness: f = 64/Re in laminar flow, and a correlation such as Blasius or Colebrook–White in turbulent flow.
- What is the difference between head loss and pressure drop?
- They describe the same energy loss in different units. Pressure drop ΔP is in pascals; head loss hL is the equivalent height of a column of the same fluid, in metres, and the two are related by hL = ΔP / (ρ·g). Head is the more convenient form when sizing pumps, because pump curves are published as head against flow.
- What does the Froude number tell you about open-channel flow?
- The Froude number, Fr = v / √(g·d), compares the flow velocity with the speed of a surface wave. Fr below 1 is subcritical flow — deep, slow, and controlled from downstream. Fr above 1 is supercritical — shallow, fast, and controlled from upstream. Fr near 1 is critical flow, where the specific energy is at a minimum and the surface is unstable.