A 2D wind tunnel for aeromodelers and anyone who likes watching air misbehave. It streams a flow past an airfoil and draws the speed field, the vorticity, smoke streaklines and the lift/drag vectors while you turn the angle of attack. You can also draw your own shape, cut a wing into wing + flap, animate the control surfaces, and watch the wake fall apart when you push the angle too far.

It is qualitative, not validated CFD. Lattice units stand in for physical ones, so it gets the shape of the flow right (stagnation point, wake, suction over the top, separation as the angle grows) and the actual numbers wrong. Use it for intuition and for a demo that looks good on a projector, not for sizing a real wing.

Written in Go with Ebitengine. One executable, nothing to install alongside it.

Grab a prebuilt binary from the latest release. You do not need Go or any developer tools.

With Homebrew, one command:

brew install --cask crgimenes/tap/kutta

Or by hand:

1. Download kutta-darwin-universal.zip and double-click it to unzip. You get kutta.app.
2. Move kutta.app to your Applications folder.
3. Double-click it to run.

The app is signed and notarized by Apple, so it opens normally. The single universal build runs on both Intel and Apple Silicon, so there is no architecture to choose.

If macOS says "kutta.app is damaged and can't be opened" or complains about an unidentified developer:

• Make sure the download finished, and unzip before opening (do not run the app from inside the .zip). Re-download if in doubt.

• Right-click kutta.app, choose Open, then confirm with Open in the dialog.

• If it still refuses, open Terminal and run (adjust the path if you did not move it to Applications):

  xattr -dr com.apple.quarantine /Applications/kutta.app

Download the .exe for your machine and double-click it. Windows SmartScreen may warn you because the app is not from the Microsoft Store: click More info → Run anyway.

Download the matching .gz, then decompress and run:

gunzip kutta-linux-amd64.gz
chmod +x kutta-linux-amd64
./kutta-linux-amd64

With Go installed:

go run .

On macOS and Windows there is nothing else to install. On Linux, Ebitengine needs Cgo and the system development libraries, so build with CGO_ENABLED=1 after installing the packages from the Ebitengine install guide (on Debian/Ubuntu: libgl1-mesa-dev, libasound2-dev, libxcursor-dev, libxi-dev, libxinerama-dev, libxrandr-dev, libxxf86vm-dev, pkg-config).

Type a code in the field at the top (2412, 0012, 23012, ...) to pick any NACA 4- or 5-digit foil, not just the ones on Tab. And if you type neko in that field, you get a cat. It has terrible aerodynamics. That is the point.

Press E. Draw a shape with the pen, drag its vertices, and curve an edge by pulling out a Bézier handle. Cut a closed outline at a vertex and rejoin two loose ends to split one airfoil into separate parts, which is how you turn a wing into wing + flap that each follow the real profile.

Tab switches between geometry and animate. In animate you scrub a timeline and drop a keyframe for each part's pose, so a flap can deploy and retract on a loop while the flow keeps running. Scenes save as .afoil, a small Filo s-expression file; see examples/ for a few (flap.afoil, neko.afoil).

• Solver (lbm): a 2D Lattice-Boltzmann method (D2Q9, BGK). An open channel with a free stream from the left; the body is a no-slip wall via half-way bounce-back. Forces come from a pressure integral over the body faces, so it captures form drag and lift. Skin friction is ignored, which means drag is understated. That is a known limit, not a bug to file.
• Geometry (foil): NACA 4- and 5-digit airfoils straight from their closed-form equations. A whole catalog with nothing stored on disk.
• Scenes (scene, sceneio): multi-object shapes with per-vertex Bézier handles, cuts, and keyframe animation, read and written as .afoil.
• Visualization (viz): color maps for the scalar fields and a smoke-tracer particle system pushed around by the velocity field.
• App (main.go, game.go, editor.go): the Ebitengine loop, the editor, and the native macOS/Windows menu (via glaze).

lbm, foil, scene and viz carry no rendering dependency and are unit tested headlessly. cmd/snapshot renders the fields to PNG without a GPU, which is how the physics gets sanity-checked: lift rising with angle of attack, the drag bucket, the force signs coming out right.

See LICENSE.

• minigui: a tiny immediate-mode GUI for Ebitengine.
• filo: a small scripting language safe to embed in Go programs.
• glaze: WebView desktop apps in Go, cgo-free.
• neko: the classic desktop cat chasing your pointer, in Go.

More at github.com/crgimenes and crg.eti.br.