This simulator recreates the classic Reynolds dye-injection experiment — a colored thread injected into a pipe reveals whether the flow stays as an orderly laminar streamline, breaks up in a transitional band, or mixes fully as turbulent flow. Adjust imposed mean velocity, internal bore, viscosity, density, test-section length and the dye needle's radial injection offset, and watch the dye pattern, velocity-profile reference and Reynolds number respond together.
• A real-time 3D scene of the conditioned header reservoir with internal screens, the dye reservoir and fine injection needle at a selectable radial offset, the long transparent observation tube (cutaway removes the front enclosure), the outlet regulating valve and collection tray, a magnified velocity-profile traverse, an entrance-length ruler, and an optical viewing lamp/record station, with home view, focus-selected-part, show-full-enclosure, exploded view, auto-rotate, expand and show/hide labels controls. • An Equipment laboratory tab with a labeled parts index (header, injector, tube, outlet, profile, length, viewer) and click-to-inspect component callouts. • Six experiment controls: imposed mean velocity (0–1.5 m/s), internal test bore (5–100 mm), dynamic viscosity μ (0.5–50 mPa·s), liquid density ρ (800–1,200 kg/m³), test-section length (0.2–12 m) and dye-needle radial offset r/R (0–0.8, dimensionless). • Playback controls: pause/resume, advance 0.1 s, advance 1 s, and four playback speeds (10× slow motion, real time, 10× faster, 1 minute per second), plus start/stop animation and toggle-dye-injection actions. • A Curves & measurements tab with a velocity-profile-references chart, two live charts (Reynolds number history, and mean velocity vs. reference peak), the governing equations (Reynolds number, laminar and turbulent illustrative velocity profiles, entrance-length guides) and snapshot measurement readouts. • An Experiments tab with four guided fixtures (quiet laminar thread, turbulent mixing, transition uncertainty, short developing section) and a Model verification bench that runs independent deterministic checks against a fresh model without disturbing your live experiment, plus a timestamped event log and a copyable trial report. • A Learn & assess tab with guided lessons, a knowledge-check quiz with reset, and a written model-scope statement with a technical-background reference link.
At low Reynolds number, viscous forces damp out disturbances and a dye thread injected into the flow stays narrow and coherent, following the parabolic laminar velocity profile where centerline speed is twice the mean. As Reynolds number rises — by increasing velocity or reducing viscosity — inertial effects begin to dominate, disturbances can grow rather than decay, and the dye spreads across the section as the flow becomes turbulent.
The simulator treats the transition region (roughly Re 2,300–4,000) honestly as a band of uncertainty rather than a precise threshold, since real transition also depends on inlet disturbances, surface roughness and flow history that a simple Reynolds-number criterion cannot capture on its own.
The entrance-length ruler compares your test-section length against a guide for how far downstream of the header the flow needs to travel before its velocity profile is fully developed — approximately Le ≈ 0.05·Re·D for laminar flow, or an illustrative 10D for turbulent flow. If the available section is shorter than this guide (as in the 'short developing section' experiment), the displayed profile remains a fully-developed reference rather than a claim about the actual, still-developing flow in a too-short test section.
This is a steady, Newtonian, incompressible-liquid model where properties (density, viscosity) are direct user inputs rather than a temperature/composition correlation, and the dye and mixing animations are illustrative visualizations of mixing behavior — not a computational fluid dynamics or resolved-turbulence solution. There is no pump curve, pressure-loss solution, compressibility or cavitation model, and the one-seventh-power turbulent profile is a normalized illustrative mean profile, not a wall-shear or viscous-sublayer calculation.
No. Reynolds number predicts a regime tendency — laminar, transitional or turbulent — but this simulator does not solve the instantaneous three-dimensional flow field or resolve individual eddies. The wavy dye pattern is an illustrative visualization of mixing behavior, not a CFD result.
Centerline speed is exactly twice the mean speed for the parabolic laminar profile, since the area-average of a parabola over a circular cross-section is half its peak (centerline) value — this relationship is built into the simulator's laminar velocity-profile reference.
Real transition from laminar to turbulent flow depends on more than Reynolds number alone — inlet disturbances, surface roughness and flow history all matter. The simulator marks Re 2,300–4,000 as a transition band rather than claiming a single exact switching point, which better reflects real pipe-flow behavior.
The simulator's entrance-length ruler flags that the flow may not be fully developed at your outlet, and the displayed velocity profile remains a fully-developed reference shape rather than a resolved calculation of the actual developing flow — as demonstrated in the 'short developing section' experiment.