🥣Non-Newtonian Fluid Simulator - Rheology Models, Pipe Flow, Oobleck, Ketchup

How to use Non-Newtonian fluids

1. 1Choose a fluid preset, or switch the model and set μ, K, n, τ_y and so on
2. 2On Rheology models compare viscosity and stress curves across fluids
3. 3On Pipe flow set the radius and pressure gradient and watch the profile, plug and flow rate
4. 4On Oobleck and Ketchup & thixotropy use the presets and buttons to see impact stiffening, tapping and viscosity over time
5. 5On Falling-ball viscometer pick a ball and tube, or enter a measured distance and time to get the viscosity

FAQ

What causes shear thinning and shear thickening?

Shear-thinning fluids contain long molecules, fibres or particle clusters that get stretched, aligned or broken up as the flow speeds up, so resistance drops; ketchup, paint and blood behave like this. Shear thickening is typical of dense suspensions such as cornstarch in water: in slow flow the grains are lubricated by thin water films, but fast shear pushes them into direct frictional contact, forming force chains, and the viscosity shoots up.

Why do you have to tap a ketchup bottle?

Ketchup has a yield stress of roughly 15–30 Pa and sits still like a soft solid below it. Upside down, the weight of the ketchup in the neck only produces a wall stress of order ρgR/2, about 28 Pa for a 5 mm neck, just short of it. A tap briefly multiplies the effective gravity and the wall stress, so it starts to flow, and the shearing breaks down the internal structure (thixotropy) and lowers the yield stress. That is why it often gushes after a few taps.

Why can you run on oobleck but sink if you stand still?

A fast footstep gives the grains no time to move aside, so a jammed, solid-like zone spreads rapidly under the foot and supports a large force; the foot sinks only slightly before it lifts off. Standing still shears the mixture slowly, the grains slide past each other on their water films, it behaves like a liquid and you sink. The tool uses a simplified critical-shear-rate model with a solid-like stress for a qualitative demonstration.

Why does a Bingham fluid show plug flow in a pipe?

In a round pipe the shear stress rises linearly from zero at the centre to τ_w = (ΔP/L)R/2 at the wall. A Bingham or Herschel–Bulkley fluid does not shear wherever the stress is below its yield stress, so everything within r_p = 2τ_y L/ΔP of the centre moves as one block and shearing happens only in the ring near the wall. Below a pressure gradient of 2τ_y/R nothing flows at all.

When is a falling-ball viscometer accurate?

Stokes' law v = Δρgd²/(18η) needs a Reynolds number well below 1, ideally below 0.1, so a small, slow ball in a viscous liquid, and a tube much wider than the ball or else the Faxén wall correction. The tool warns when Re is too high and estimates the speed with the Schiller–Naumann correction. For a non-Newtonian fluid you only get the apparent viscosity near the shear rate v/d, and with a yield stress the ball hangs still once Y = τ_y/(Δρgd) exceeds about 0.048.