Sketch CFD

For iPhone and iPad

Sketch CFD

Sketch a shape, see the flow.

An educational app for learning computational fluid dynamics (CFD). Draw walls, inlets, fans, and heaters, or photograph a sketch drawn on paper, and watch the flow, gas mixing, and heat develop as the calculation runs.

Coming soon to the App Store See the features

Requires iOS or iPadOS 16.4 or later. In English.

Air flowing past a cylinder, from the app’s launch animation: bands of blue, amber, and orange dye show the vortices that shed behind the cylinder one after another, simulated with the app’s own solver.

In the app

  • The Box purge example: nitrogen enters a box at the lower left and pushes the air out through a slot at the upper right. The box is colored by oxygen share, green where it is low, with flow arrows.
    Gas share during a purge
  • The draw tray over the Duct with a cylinder example: the Line, Rect, Circle, Curve, Free, Dim, and Erase tools, the roles Wall, Inlet, Vacuum, Open, Porous, Source, Hot, Probe, and Guide, and Grid snap with a 15° angle step. Above the tray, air from the inlet at the left flows past a cylinder, which sheds vortices, colored by speed.
    Draw tools and part roles
  • Check the imported sketch: the parts recognized on the sample paper drawing, and the list of 5 parts found, among them a hot wall at 120 °C and an air inlet at 20 L/min with an assumed temperature to check.
    Review of the sample paper drawing
  • The Lid-driven cavity example, colored by speed from 0 to 0.139 m/s: the lid moves to the right along the top and turns the air in the square box into one large eddy.
    Speed in a lid-driven cavity
  • Open an example: the examples in groups, starting with Flow and forces and Heat and buoyancy, each with a one-line description.
    The 14 examples

Draw it

Draw lines, rectangles, circles, curves, freehand strokes, and dimensions in mm, with snapping, undo, and redo.

Give each part a role: wall, inlet, fan, open edge, filter, gas source, hot or cold wall, or probe.

The iPad layout with the Rect tool selected: a bar over the canvas lists the roles to draw as, from Wall to Guide, and the Parts panel lists the nine parts of the Box purge sketch, such as the N2 inlet at 10.0 L/min and two probes.

Photograph a sketch drawn on paper

  1. Draw on plain white paper with the 18 symbols shown in the app.
  2. Photograph the sheet. The app reads the lines and symbols and builds a sketch over the drawing.
  3. Check each part on the review screen and type the values you wrote. This version does not read handwriting.
  4. Set the scale and run it.

The photo is read on your device and is not uploaded. The sample drawing is free; importing your own photos is part of Sketch CFD Pro.

The review screen of the paper import with the sample drawing: on the left, the parts recognized on the sheet; on the right, 5 parts found and 1 value assumed, and the labels written on the sheet, each with a field for its value.

Simulate it

The flow runs live and follows every change you make.

  • Speed m/s
  • Pressure Pa
  • Temperature °C
  • Gas share %
  • Show any of these fields, with flow arrows.
  • Follow particles in the flow, such as dust settling in a chamber.
  • Read probes, forces on parts (N), port flows (L/min), and filter pressure drops (Pa).
  • Help explains the lattice Boltzmann model and what it leaves out.
The Room with a radiator example, colored by temperature from 20 °C to 52 °C with flow arrows: warm air rises from the radiator at the lower left and circulates through the room. The Results panel lists the run, the probe readings at ankle and head height, and the force on the radiator.

Learn with 14 examples

Each example has notes on what it shows, a published value to compare with where there is one, and what to try. All 14 are free to run and explore.

Flow and forces

  • Lid-driven cavity
  • Channel flow check
  • Backward-facing step
  • Duct with a cylinder
  • Airfoil in a wind tunnel

Heat and buoyancy

  • Water heated from below
  • Room with a radiator
  • Hot and cold water in a tee
  • Fume hood capture

Mixing, purging and dispersion

  • Box purge
  • Round jet
  • CO2 leak in a lab
  • Wind around a building

Particles

  • Dust settling chamber
The Fume hood capture example, colored by fume share: fume rises from a hot plate on the floor, and a draft from the right bends the plume past the canopy hood toward the breathing zone at the left.

Free and Sketch CFD Pro

Free

  • Run and explore all 14 examples.
  • Draw walls of any shape in a wind tunnel (200 mm × 100 mm of air).
  • Coarse and Medium resolution.
  • Projects, files, and the help.

Sketch CFD Pro adds

  • Design anything: inlets, outlets, fans, filters, heaters, gas sources, and probes, in any size.
  • Gases and liquids, heat and buoyancy, and particles.
  • Fine meshes for more detail.
  • Edit the examples.
  • Import your own paper drawings from a photo.
  • Reports with the run settings, probe readings, and the sketch.

Sketch CFD Pro is an auto-renewable subscription, monthly or yearly, with a free trial for eligible new subscribers. If your subscription ends, your sketches still open and run. See the subscription terms and the questions about Sketch CFD Pro.

On your device

Drawing and calculation run on your iPhone or iPad. Your sketches and photos stay on your device.

  • Works offline

    Drawing, the calculation, and the paper import need no connection.

  • No account

    Open the app and start. There is nothing to sign up for.

  • No ads

    The app shows no advertising.

  • Apple Pencil

    Apple Pencil draws while your fingers pan and zoom. A keyboard, trackpad, or mouse works on iPad.

The Sketch CFD app icon: a colored-pencil drawing of air flowing left to right through a box and around a sphere. The streamlines change from blue to amber to orange, with two small eddies behind the sphere.

Educational use only

Sketch CFD is for education and learning only. Its results are estimates from a simplified two-dimensional model. The calculation is verified against published benchmark cases, such as the lid-driven cavity, flow around a cylinder, and a heated square cavity, but it has not been validated against measurements or tested in real-world scenarios. It is not a substitute for professional engineering analysis, testing, or applicable codes and standards. Do not use it for safety-critical, medical, or compliance decisions. You use the results at your own risk; to the extent the law allows, Journey On is not responsible for any loss or decision based on them. See the Terms of Use.

Sketch CFD for iPhone and iPad

Learn fluid flow by sketching. Requires iOS or iPadOS 16.4 or later.

Coming soon to the App Store

Questions? Email support@journeyon.co or read the support page.