Wind Tunnel guide

Every control

The panel on the right, top to bottom. On a phone it is the sheet at the bottom of the screen; press its bar to open it.

Everything you choose is remembered on this device, except a silhouette of your own, which stays only for this visit. Copy a link carries the island, the wind, Re, the look and the colours, so a friend opens the same tunnel.

Load and save

Your own island, and the two saves. The line under the silhouette button names the island, how many cells it spans across the wind, and its Re.

Open a silhouetteButton: Any picture from your device becomes an island: its dark part, or its opaque part when it has transparency; if the border reads as land, the picture is taken the other way round. It stays for this visit and is never uploaded.
PNGButton: This moment as a PNG at the size chosen below (E or S).
MP4Button: Records the flow from now as an MP4 for the seconds chosen below. While it records, the picture on screen holds still and the button counts the per cent.
CancelButton: Stops a recording. Nothing is saved.
PauseButton: Pauses or plays the sea (Space). Land can be drawn while it is paused.

Save

How large both saves are, and how long the video is. The line under the chips names the file before you make it. Copy a link puts this very tunnel on the clipboard.

1080p · 4KPick one: The size of both saves, always 16:9. When the frame on screen has another shape, the save is cut from it, and the island stays.

1080p: 1080p: 1920 × 1080.

4K: 4K: 3840 × 2160. It asks a lot of the graphics card; if a video stutters, choose 1080p.
5 · 10 · 20 · 30 sPick one: How long the MP4 is, at 30 frames a second. The line under the chips names the size, the codec, the length and about how large the file can be.

5: Five seconds.

10: Ten seconds.

20: Twenty seconds, the length it opens with.

30 s: Thirty seconds, the longest.
Copy a linkButton: Copies a link to this tunnel (L): the island, the wind, Re, the look, tracers and the colours. Whoever opens it sees the same flow start. A line under it says when the link is copied.

Island

Where the wind blows: the presets, the real islands, the nine famous vortex streets and their satellite photos. A preset sets the island, the wind, Re, the look and the colours in one press; each island starts with its own prevailing wind and its Re at 150.

Guadalupe, as photographed · Sri Lanka monsoon · Textbook cylinder, Re 100 · Turbulent, Re 2000 · Draw your ownPick one: Ready starts: Guadalupe as the satellite photographed it, Sri Lanka in the monsoon, the textbook cylinder at Re 100, a turbulent wake at Re 2000, and open sea to draw on. Each one sets the island, the wind, Re, the look and the colours.
Sri Lanka · Lakshadweep · Andaman · Hainan · Taiwan · Japan · Hawaiʻi · Tasmania · Madagascar · Mauritius · Crete · Sicily · Britain & Ireland · Iceland · Cuba · Cylinder · DrawPick one: Fifteen real islands, a cylinder and open sea. Each starts with its own prevailing wind and Re 150 (Draw at 300).

Sri Lanka: Sri Lanka, in the south-west monsoon (from 225°).

Lakshadweep: Lakshadweep, coral atolls off Kerala, the monsoon from the west (270°).

Andaman: The Andaman Islands, in the south-west monsoon (225°).

Hainan: Hainan, in the north-east winter monsoon (45°).

Taiwan: Taiwan, in the north-east winter monsoon (45°).

Japan: Japan, in the north-west winter monsoon (315°).

Hawaiʻi: Hawaiʻi, in the trade winds (60°).

Tasmania: Tasmania, in the westerlies of the Roaring Forties (270°).

Madagascar: Madagascar, in the south-east trade winds (110°).

Mauritius: Mauritius, in the south-east trade winds (120°).

Crete: Crete, in the summer meltemi (340°).

Sicily: Sicily, in the maestrale (315°).

Britain & Ireland: Britain and Ireland, in the prevailing west-south-west wind (240°).

Iceland: Iceland, the wind from the south-west (225°).

Cuba: Cuba, in the trade winds (70°).

Cylinder: A round post, the textbook body: the cleanest street, and the Strouhal number to check against 0.2.

Draw: Open sea and a west wind, for land you draw yourself.
Guadalupe · Jeju · Canary Islands · Heard Island · Juan Fernández · Madeira · Socotra · Cape Verde · RishiriPick one: Nine islands whose vortex streets satellites photograph, each in the wind of its best-known photo and Re 150. Each has a NASA photo for Satellite photo.

Guadalupe: Guadalupe, off Baja California, in the north-north-west wind (340°): the most photographed street of all.

Jeju: Jeju, off Korea, in the north-west winter monsoon (320°).

Canary Islands: The Canary Islands, in the north-east trade wind (30°).

Heard Island: Heard Island, a lone volcano in the westerlies of the Southern Ocean (270°).

Juan Fernández: Juan Fernández: Alejandro Selkirk, off Chile, in a south-west wind (225°).

Madeira: Madeira with Porto Santo and the Desertas, in the north-east trade wind (30°).

Socotra: Socotra, in the south-west monsoon (225°); its photo is a wake in dust.

Cape Verde: Cape Verde, ten islands in the north-east trade wind (40°).

Rishiri: Rishiri, off Hokkaido, in the north-west winter monsoon (315°).
Satellite photoOn or off · starts off: Satellite photo (C): the NASA photograph of this island's own vortex street, over the lower right of the frame, beside the simulation. Only the famous vortex islands have one; the × closes it. See the islands.

Wind

Which way the wind blows, the Reynolds number of the largest island and what it means, and how fast the sea plays. The reading under them is the live flow.

FromSlider · 0 to 359 · starts at 225: The compass bearing the wind blows from. The map turns, not the wind: it always blows left to right, and the needle shows north. Let go and the land turns under the running sea.
ReSlider · 0 to 1000 · starts at 349: The Reynolds number of the largest island, from 30 to 3000. It sets the water's viscosity; the wind's speed stays the same.
Slow · Normal · FastPick one: How many lattice steps the sea takes each frame: Slow halves them, Fast doubles them. It changes how fast the flow plays, not the physics.

Look

Five ways of showing the same sea, specks that ride it, and labels that explain it.

Ink · Paper · Vorticity · Cloud · SpeedPick one: The same sea five ways (1 to 5).

Ink: Ink: a night sea, silver streaklines, saffron and pearl dye by which way it spins.

Paper: Paper: the flow printed in sepia on paper.

Vorticity: Vorticity: the spin itself, teal one way and vermilion the other. See vorticity.

Cloud: Cloud: the wake as a satellite sees it, white cloud over a deep blue-grey sea.

Speed: Speed: the water against the wind's own speed, cold where the sea stalls, warm where it races.
TracersOn or off · starts off: Two thousand specks riding the flow (T). They are saved in the PNG and the MP4 too.
Explain the pictureOn or off · starts off: Labels the picture while it runs (X): the body, the shear layers that peel off its sides, an eddy shed every so many steps with the live Strouhal number, the two rows of the street with their opposite spins, and the sponge at the far end where the flow is calmed.

Colour

Your own colours for the flow. Every look honours them: Ink and Paper use all five; Vorticity, Cloud and Speed keep their own ramps, but the ramp runs from Stripes to Ink, so a brand colour still shows. A palette sets all five at once.

Night · Paper · Satellite · Blueprint · Mono · WarmPick one: Six sets of the five colours below. Picking one sets all five; changing any colour by hand lets go of the chip.

Night: Night: each look's own colours, as the tool opens.

Paper: Paper: the sepia print colours.

Satellite: Satellite: cloud white on a blue-grey sea, as the NASA photos see it.

Blueprint: Blueprint: white lines on a deep blue, for a diagram.

Mono: Mono: black on white, for print and line art.

Warm: Warm: ochre on cream.
SeaColour · starts #121823: The sea, the ground of the picture. With Transparent background (PNG) on, the PNG leaves it out.
StripesColour · starts #434e5e: The thin lines the dye draws (streaklines) in Ink and Paper; in Vorticity, Cloud and Speed, one end of the colour ramp.
InkColour · starts #ffbf69: The ink the coast sheds into the wake in Ink and Paper; in the other three looks, the ramp's other end. A brand colour goes here.
LandColour · starts #27231f: The island, and any land you draw.
TracersColour · starts #ffdfaa: The specks Tracers draws.
Transparent background (PNG)On or off · starts off: The PNG keeps the island, the ink and the stripes and leaves the sea see-through (alpha), to lay over a page, a slide or a video. The MP4 always keeps its sea.
Default coloursButton: Puts the five colours back to the look's own.

Draw

Your hand in the frame: drag to raise land anywhere, shift-drag to sink it.

BrushSlider · 0.5 to 4 · starts at 1.4: How large your hand is when it raises or sinks land, from 0.5 to 4 % of the frame's height.

Reset

ResetButton: Starts the island again from a calm sea (R). The wind, Re and the look stay as they are.