A straight channel.
A curved front.
Release a dye pulse, change the pressure and viscosity, and watch the centre outrun fluid near the walls.
Reduced motion is enabled. Choose still frames with the controls.
The centre pulse travels 1.5 times the mean speed.
What this cell reveals
Exact established plane Poiseuille flow between fixed parallel walls. Gap H=2 mm, density ρ=1000 kg/m³ and observation length=0.4 m. Mean speed is GH²/(12μ); centre speed is 1.5 times the mean. Left dial: pressure gradient 0–200 Pa/m. Right dial: mean speed 0–350 mm/s.
Re =ρ Umean(2H)/μ
Seven ideal, nondiffusing pulses start together at t=0. Violet samples your chosen y/H. Each travels u(y)t, disappears at the outlet and never wraps back. Changing pressure or viscosity selects another established steady profile, without calculating start-up.
This infinite-width model uses an invented cutaway, not Reynolds's pipe. The floor, ports and removed cover frame a section without adding mathematical walls. It omits turbulence, diffusion, entrance effects and transverse motion. The Re≥2000 warning questions laminar applicability; it is not a universal transition threshold. No general regularity proof follows.
MIT: exact plane pressure-driven flow ↗
NASA Glenn: Reynolds similarity parameter ↗