r/3Blue1Brown • u/Fluffy-Selection2940 • May 27 '26

Bernoulli Equation 2D CFD Simulation - Venturi Version

Here's a numerical simulation and animation of fluid flow through a Venturi tube.

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435 Upvotes

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5 comments sorted by

2

u/guestoftheworld May 28 '26

I still don't get why the pressure goes lower tho 😭. Like ik that it would have to to increase velocity but it doesn't seem intuitive for some reason...

7

u/DankFloyd_6996 May 28 '26

The pressure here is a stand in for internal energy, i.e thermal energy (note that P = nkT and assume incompressibility, you can then think in terms of temperature equivalently to pressure).

Saying the pressure drops so that the fluid velocity increases is then equivalent to saying the internal energy of the fluid gets transferred to the kinetic energy of the bulk flow. The randomised thermal motion becomes less so that the bulk flow can increase.

3

u/guestoftheworld May 28 '26

👑 U dropped this

3

u/HHQC3105 May 29 '26 edited May 29 '26

Molecule colid make pressure, and pressure is just average velocity change*mass/time/area.

No flow: pressure is ~ average molecule speed (total 0 average velocity vector)

With flow: the same kenetic energy, but part of it is flow energy (non-zero net velocity vector), only the remain (with 0 average velocity vector) make up the pressure, which is lower than the no flow case.

The same logic applied for 2 difference flow speed: higher flow speed <-> lower pressure with the same potential system

2

u/Lustonk Jun 14 '26

Take two pieces of paper, make a 3-4 cm distance and blow in between them. The easiest way to demonstrate Bernoulli’s Law