Flow Visualization One flow — wind over a hump, separating into a bubble on the lee side — told three ways. Top: a smoke line from a nozzle (streakline) traces the shear layer that lifts off. Middle: a wire pulsing sheets of bubbles (timelines) shows the speed at every height, bending backward near the wall where the flow reverses. Bottom: little wall tufts lie down where the flow is attached and flip red where it isn’t, pinning the separation and reattachment points. The journey: you can’t see air, so every technique tags something that moves with it — smoke, bubbles, threads, or (for shockwaves) the bending of light itself.