Press and drag with a mouse or finger to use the smoke wand. With the keyboard, when the tunnel is focused: Space or Enter puffs smoke in front of the car, 1 to 4 change the view, P pauses, C clears the smoke, M toggles sound, and the up and down arrows change the air speed.
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Notes from the tunnel
Car makers test in wind tunnels where a rolling road runs under the car at the same speed as the air, so the ground moves the way it does on the road. The striped belt here is doing the same job.
Aerodynamic drag grows with the square of speed: double the speed and the drag roughly quadruples. Move the air speed slider and watch the force bars.
A smooth, gently sloping roof keeps the air attached to the body for longer. Where it finally lets go, at the sharp edge of the tail, it leaves a turbulent wake. Switch to Swirl view to see it. Many modern road cars have a drag coefficient of roughly 0.25 to 0.35.
Low pressure under the car pulls it towards the road. Pressure view shows it in blue.
Controls
Press and drag in the air to use the smoke wand. With the tunnel focused: Space puffs smoke, 1 –4 change the view, ↑ ↓ change the air speed, P pauses, F shows the speed meter, C clears the smoke and M toggles sound.
How it works
Velocity is solved on a grid with Jos Stam’s “stable fluids” method (semi-Lagrangian advection, vorticity confinement and a pressure projection). Smoke rides on a grid twice as fine using MacCormack advection, and the car’s outline is read straight from its SVG drawing.
This is a two-dimensional sketch on a coarse grid, a real “stable fluids” solver but nothing like an engineering simulation. The car is an original design drawn for this page, and the tunnel is fictional.