Sketch CFD Terms of Use

Last updated: October 17, 2026

These Terms of Use (“Terms”) are an agreement between you and Omnis Dragon LLC, doing business as Journey On (“Journey On”, “we”, “us”). They cover the Sketch CFD app for iPhone and iPad (“Sketch CFD” or “the app”) and the Sketch CFD Pro subscription. Please read them in full, and especially section 4 (Educational use only), section 11 (No warranty) and section 12 (Limitation of liability). By downloading or using the app, you agree to these Terms. If you do not agree, do not use the app.

1. Who we are

Sketch CFD is made by Omnis Dragon LLC, a Tennessee limited liability company doing business as Journey On, 116 Agnes Rd, Ste 200, Knoxville, Tennessee 37919-6306, United States. Email: support@journeyon.co.

2. Apple’s license agreement and these Terms

You get the app from Apple’s App Store. Your license to use the app comes from Apple’s Licensed Application End User License Agreement (the “Standard EULA”, https://www.apple.com/legal/internet-services/itunes/dev/stdeula/), with Journey On as the licensor. These Terms add terms that are specific to Sketch CFD. They do not replace the Standard EULA, and you should read the two together. If they conflict, the Standard EULA governs your license to the app, and these Terms govern everything else.

Apple’s Media Services Terms and Conditions govern your Apple Account, payments, renewals and refunds.

3. Who may use the app

• You may use the app if you can form a binding contract where you live. If you are under the age of majority where you live, use the app and buy a subscription only with the permission of a parent or guardian. That parent or guardian agrees to these Terms for you and is responsible for your use.
• You may not use the app if you are in a country that is subject to a U.S. Government embargo or that the U.S. Government has designated as a “terrorist supporting” country. You may not use it if you are on any U.S. Government list of prohibited or restricted parties.
• If you use the app for an organization, you agree to these Terms for that organization as well.

4. Educational use only

4.1 What Sketch CFD is for. Sketch CFD is an educational tool. Use it to learn how fluid flow, gas mixing, heat transfer and particle transport behave, and to learn how computational fluid dynamics (CFD) works: draw a sketch, then simulate it. Use it for education, learning, teaching and exploring ideas only.

4.2 Not a substitute for professional work. Sketch CFD does not replace any of the following:

• a qualified engineer or other professional;
• physical testing and measurement;
• three-dimensional analysis with validated engineering software;
• the codes, standards and regulations that apply to your work. These include those for ventilation, fume hoods and local exhaust, clean rooms, heating, ventilation and air conditioning (HVAC), buildings, fire and smoke control, gas detection, confined spaces, purging and inerting, and occupational exposure limits.

4.3 Never use it for safety-critical, medical, life-safety or compliance decisions. Do not use Sketch CFD or its results to design, size, approve, certify or operate any real system. Do not use them to decide whether a place, process or product is safe or meets a code, standard or regulation. This covers, for example:

• breathing air and oxygen levels;
• toxic, flammable or asphyxiant gases;
• exposure of people to gases or particles;
• fume capture, smoke and fire;
• pressure, temperature, heat loads and forces on structures;
• any medical or health matter.

Some built-in examples show situations that involve safety: Fume hood capture, CO2 leak in a lab, Box purge, and the oxygen threshold on the Live tab. They are teaching examples. They do not show that any real installation is safe.

4.4 You are responsible for how you use the results. You decide whether and how to use anything Sketch CFD shows, and you bear the risk of that decision. If you share results, reports or sketches with others, do not present them as validated, certified or professional engineering results.

4.5 No warranty, limited liability. Sketch CFD and its results are provided “as is”, without warranty of any kind, including any warranty of accuracy (section 11). To the maximum extent permitted by law, Journey On is not liable for any loss, damage, injury or claim that results from using or relying on Sketch CFD or its results (section 12). These sections add to the “No Warranty” and “Limitation of Liability” sections of Apple’s Standard EULA and are consistent with them.

5. Accuracy and limits of the model

5.1 Results are estimates from a simplified model. Sketch CFD calculates with a simplified two-dimensional model, the lattice Boltzmann method on a square grid. A planar model is a slice of a set depth and assumes that nothing changes across that depth. An axisymmetric model assumes a round part with no swirl. Real flows are three-dimensional, so results can differ from real behavior by a large amount.

5.2 What the model leaves out or simplifies.

• Three-dimensional flow.
• Compressible and supersonic flow, combustion and chemical reactions, free surfaces such as a water level, and multiphase flow.
• Fluid properties that change with temperature. Viscosity and diffusivity stay fixed, and a heated gas does not expand. Warm fluid and light or heavy gases act only through a buoyancy force.
• Turbulence. It is represented by one simple eddy-viscosity model, and no turbulent benchmark case has been checked. Turbulent jets, rooms and wakes are therefore rough estimates. Two-dimensional jets spread several times faster than real jets.
• Heavy gases. A heavy gas such as carbon dioxide spreading along a floor may arrive earlier than it would in reality.
• Hot gases. At high temperatures the real viscosity and diffusivity of a gas are much larger than the fixed values the model uses.
• Coarse grids. On a coarse grid the model raises the viscosity to keep the calculation stable, so the flow behaves as if it were slower or more viscous than the values entered.
• Speed. Results hold only at moderate flow speeds on the chosen grid; the app warns when a run goes beyond them.
• Open edges. They take gas in as if from still air.
• Particles. They do not affect the flow, have no inertia and do not collide, and each run uses one particle size. Particle results are random and differ from run to run.
• Porous parts. Capture of particles and tracer by a filter follows the value you set; it is not calculated from a theory of capture.
• The paper import. It can miss or misread parts, and it does not read handwriting. Check every part, role and value on the review screen before you use an imported sketch.

Help and shortcuts > Model in the app describes the model in more detail.

5.3 Verified against benchmark cases, not validated against the real world. The calculation has been verified against published benchmark cases and exact solutions. Its results were compared with published values, and each comparison had to fall within a set tolerance: 1% for exact solutions and mass or heat balances, 2% for steady benchmarks, 3% for unsteady peaks and recirculation lengths, and 5% for gravity currents. The cases are:

• flow in a lid-driven square cavity at Reynolds numbers 100 and 1000: Ghia, U., Ghia, K. N. and Shin, C. T. (1982), Journal of Computational Physics 48, 387–411;
• laminar flow around a cylinder in a channel, benchmark cases 2D-1 and 2D-2: Schäfer, M. and Turek, S. (1996), in Flow Simulation with High-Performance Computers II, Vieweg, 547–566;
• flow over a backward-facing step at Reynolds number 389, reattachment length: Rose, A. and Simpson, B. (2000), First NAFEMS Workbook of CFD Examples, and Gresho, P. M. and Sani, R. L. (2000), Incompressible Flow and the Finite Element Method; geometry after Armaly, B. F. et al. (1983), Journal of Fluid Mechanics 127, 473–496;
• natural convection in a heated square cavity at Rayleigh numbers 10³ to 10⁵: de Vahl Davis, G. (1983), International Journal for Numerical Methods in Fluids 3, 249–264;
• the front speed of a gravity current: Härtel, C., Meiburg, E. and Necker, F. (2000), Journal of Fluid Mechanics 418, 189–212;
• exact solutions and balances for flow in channels, pipes and between moving walls, and for heat conduction: Bird, R. B., Stewart, W. E. and Lightfoot, E. N. (2002), Transport Phenomena; White, F. M. (2006), Viscous Fluid Flow; Shah, R. K. and London, A. L. (1978), Laminar Flow Forced Convection in Ducts;
• diffusion: Crank, J. (1975), The Mathematics of Diffusion;
• flow through porous layers (Darcy and Forchheimer laws);
• particle settling, Brownian motion and thermophoresis: Hinds, W. C. (1999), Aerosol Technology, and Talbot, L. et al. (1980), Journal of Fluid Mechanics 101, 737–758.

These checks show that the model’s equations are solved as intended for those cases. They do not show that the model represents any real room, building, product or installation. Sketch CFD has not been validated against measurements, physical tests or certified engineering software, and it has not been tested in real-world scenarios. The checks were run on a desktop computer with the same calculation code; results on an iPhone or iPad can differ slightly.

6. Your content

• Your sketches and photos stay on your device. Sketches, projects, settings, background images, and photos you import are stored and processed on your device. We do not receive them. The Privacy Policy (https://sketchcfd.journeyon.co/privacy) says more.
• What you make is yours. We claim no ownership of the sketches, reports or files you create or export. When you save or share a file, it goes where you send it, under the terms of the service you choose (for example, iCloud Drive, Mail or AirDrop).
• Files from others. If you open a sketch file someone else made, it is your responsibility that you may use it.
• Files you send us. If you send us a sketch, report, photo or screenshot with a support request, you allow us to use it only to answer that request.
• Feedback. If you send us ideas or suggestions, we may use them without any obligation to you.
• Backups are your responsibility. Deleting the app deletes the projects stored in it. Keep copies of work that matters with Menu > Projects and files > Save as a file.

7. Acceptable use

You agree not to:

• use the app in breach of any law, or of the rights of others;
• copy, modify, reverse-engineer, decompile, or try to extract the source code of the app, except as the Standard EULA, the license of an open-source component, or the law allows;
• get around, disable, or interfere with the subscription check or the limits of the free features;
• resell, rent, or redistribute the app, or offer it as a service to others;
• present results from the app as validated, certified, or professional engineering results, or use them in place of the professional work described in section 4.2;
• use the app for any purpose that section 4.3 rules out.

8. Free features and Sketch CFD Pro

8.1 Free features. Without a subscription you can:

• open and run all 14 built-in examples, change what they show, and read their live results;
• draw walls of any shape in a wind tunnel (a channel of air 200 mm long and 100 mm high, with air entering across the left edge), set the inlet speed or flow, and run it at the Coarse or Medium resolution;
• use projects, save and open files, and read the help;
• view the sample paper drawing.

8.2 What 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.

8.3 Plans and prices. Sketch CFD Pro is an auto-renewable subscription with a monthly plan and a yearly plan. The app and the App Store show the price, the period, and any free trial before you confirm a purchase. Prices are set in each country’s currency, may include taxes, and differ between countries.

8.4 Free trials. A plan may include a free trial for eligible customers. Apple decides eligibility; usually an Apple Account gets one free trial for Sketch CFD Pro. When the trial ends, the subscription starts and you are charged, unless you cancel at least 24 hours before the trial ends. If you buy a subscription while a free trial is running, any unused part of the trial is forfeited.

8.5 Automatic renewal. Payment is charged to your Apple Account when you confirm the purchase, or when a free trial ends. The subscription renews automatically for the same period at the then-current price unless you cancel it at least 24 hours before the end of the current period. Apple charges the renewal within the 24 hours before the current period ends.

8.6 Canceling. Cancel in Settings > your name > Subscriptions, or with Manage subscription in the app (Menu > About Sketch CFD). Canceling stops the next renewal; Sketch CFD Pro stays active until the end of the period you have paid for. Deleting the app does not cancel a subscription.

8.7 Refunds. Apple handles all payments and refunds. We cannot issue refunds, and we never see your payment details. To ask for a refund, go to https://reportaproblem.apple.com. Nothing in these Terms limits any right to a refund that the law gives you.

8.8 Other devices and Family Sharing. Sketch CFD Pro works on every iPhone and iPad signed in to the same Apple Account. Use Restore purchases in the app to turn it on there. Family Sharing is not available for Sketch CFD Pro.

8.9 Without a connection. Buying, restoring, and the first check of a subscription need an internet connection. After that, Sketch CFD Pro stays active without a connection, based on the last check.

8.10 When a subscription ends. You keep everything you made. All sketches and projects still open and run. Changing a design beyond the free features (section 8.1) needs Sketch CFD Pro again.

8.11 Changes to prices and features. Apple tells subscribers about price increases and asks for their agreement where its rules or the law require it. We may add, change, or remove features of the app, free or Pro. We describe significant changes in the app’s update notes.

8.12 Offer codes. Codes for Sketch CFD Pro are redeemed through Apple (Redeem a code in the app) and follow the terms shown with the code.

9. Services and terms of others

• Apple. Apple runs the App Store, your Apple Account, and the payment for Sketch CFD Pro, under Apple’s own terms and privacy policy.
• RevenueCat. The app checks your subscription with RevenueCat, Inc., which provides this service for us. The Privacy Policy says what RevenueCat receives.
• Your network provider. You must follow the terms of your mobile or internet service, and you are responsible for any data charges when the app connects.
• Links. Links in the app (for example, to these Terms or to the App Store) open in Safari or the App Store. We are not responsible for websites or services we do not run.

10. Our rights and third-party software

The app, its examples, help texts, paper notation, sample drawing, and design belong to Omnis Dragon LLC or its licensors. They are protected by copyright and other laws, and all rights not granted to you are reserved. The app includes open-source software and fonts under their own licenses, listed in the app under Menu > Third-party notices. For those components, their licenses apply. “Sketch CFD” and “Journey On” are names of Omnis Dragon LLC. The published works named in the app and in section 5 belong to their authors; naming them does not mean their authors endorse Sketch CFD.

iPhone, iPad, and Apple Pencil are trademarks of Apple Inc., registered in the U.S. and other countries and regions.

11. No warranty

You use the app and its results at your sole risk. To the maximum extent permitted by applicable law, the app, its results, and any services provided through it are provided “as is” and “as available”, with all faults and without warranty of any kind. Journey On disclaims all warranties and conditions, whether express, implied, or statutory. These include any warranty or condition of merchantability, satisfactory quality, fitness for a particular purpose, accuracy, quiet enjoyment, and non-infringement. In particular, we do not warrant that results match real-world behavior, that the paper import reads a drawing correctly, or that the app will be uninterrupted or free of errors. No advice or information from us creates a warranty. Some jurisdictions do not allow the exclusion of implied warranties or limits on statutory rights of consumers, so some of these exclusions may not apply to you.

12. Limitation of liability

To the maximum extent permitted by applicable law, Omnis Dragon LLC, its members, managers, employees, and contractors are not liable for:

• personal injury or damage to property;
• incidental, special, indirect, consequential, exemplary, or punitive damages;
• loss of profits, revenue, data, or goodwill, or business interruption.

This applies to any of these arising out of or related to your use of, inability to use, or reliance on the app or its results, however caused and under any theory of liability, even if we were told they were possible. Our total liability to you for all claims is limited to fifty U.S. dollars (US$50), as in the Standard EULA, except where the law requires otherwise. These limits apply even if a remedy fails of its essential purpose. Some jurisdictions do not allow these limits, so some of them may not apply to you. Nothing in these Terms limits liability that cannot be limited by law, such as liability for fraud, or where the law does not allow it, for death or personal injury caused by negligence.

13. Indemnity

To the extent the law allows, you agree to defend, indemnify, and hold harmless Omnis Dragon LLC and its members, managers, employees, and contractors from any third-party claim, loss, or cost (including reasonable legal fees) that arises from:

• your use of the app’s results in any design, decision, product, service, report, or advice you give to others;
• your breach of these Terms;
• content you import, open, or share;
• your breach of any law or of the rights of others.

14. Apple

You and Journey On agree to the following:

• Parties. These Terms are between you and Journey On only, not with Apple Inc. (“Apple”). Journey On, not Apple, is solely responsible for the app and its content.
• Maintenance and support. Journey On is solely responsible for any maintenance and support of the app, as described in these Terms or required by law. Apple has no obligation to provide maintenance or support for the app.
• Warranty. Journey On is responsible for any product warranty, express or implied by law, to the extent it is not effectively disclaimed. If the app fails to conform to an applicable warranty, you may notify Apple, and Apple will refund the purchase price, if any, to you. To the maximum extent permitted by law, Apple has no other warranty obligation for the app. Any other claims, losses, liabilities, damages, costs, or expenses from a failure to conform to a warranty are Journey On’s responsibility.
• Product claims. Journey On, not Apple, is responsible for addressing any claims by you or any third party relating to the app or your possession or use of it. These include product liability claims, claims that the app fails to conform to a legal or regulatory requirement, and claims under consumer protection, privacy, or similar laws.
• Intellectual property. If a third party claims that the app, or your possession and use of it, infringes that third party’s intellectual property rights, Journey On, not Apple, is solely responsible for the investigation, defense, settlement, and discharge of that claim.
• Legal compliance. You represent that you are not in a country that is subject to a U.S. Government embargo or that the U.S. Government has designated as “terrorist supporting”, and that you are not on any U.S. Government list of prohibited or restricted parties.
• Third-party terms. You must comply with applicable third-party terms when you use the app, such as your network provider’s terms.
• Third-party beneficiary. Apple and Apple’s subsidiaries are third-party beneficiaries of these Terms. Once you accept these Terms, Apple has the right, and is deemed to have accepted the right, to enforce them against you as a third-party beneficiary.
• Contact. Journey On’s name, address, and contact details for questions, complaints, or claims about the app are in sections 1 and 20.

15. Export and sanctions

You may not use, export, or re-export the app except as U.S. law and the law of the place where you obtained it allow. You may not use it for purposes U.S. law prohibits, including the development, design, manufacture, or production of nuclear, missile, chemical, or biological weapons.

16. Changes to the app and to these Terms

We may update the app and these Terms. When we change these Terms, we post the new version at https://sketchcfd.journeyon.co/terms with a new “Last updated” date. If a change materially affects you, we say so in the app’s update notes or in the app before it takes effect. If you keep using the app after a change takes effect, you accept the new Terms. If you do not accept them, stop using the app and cancel any subscription.

17. Ending these Terms

You may end these Terms at any time by deleting the app and canceling any subscription. Your rights under these Terms end automatically if you breach them. Sections 4, 5, 6, 10, 11, 12, 13, 14, 18, and 19 continue to apply after these Terms end.

18. Governing law and disputes

These Terms are governed by the laws of the State of Tennessee, United States, without regard to its conflict-of-laws rules. The United Nations Convention on Contracts for the International Sale of Goods does not apply. Before you start a legal claim, email support@journeyon.co and give us 30 days to try to resolve it. Any claim not resolved that way goes to the state courts in Knox County, Tennessee, or the U.S. District Court for the Eastern District of Tennessee, and you and we consent to their jurisdiction. If you are a consumer, you keep any protection that the mandatory law of your country of residence gives you, including the right to bring a claim in your local courts where that law provides it. The governing-law clause of the Standard EULA continues to apply to the license it grants.

19. General

These Terms, the Standard EULA, and the Privacy Policy are the whole agreement between you and us about the app. If a court finds part of these Terms unenforceable, the rest stays in effect, and that part is enforced as far as the law allows. If we do not enforce a right, we do not give it up. You may not transfer your rights under these Terms. We may transfer ours to a company that takes over Sketch CFD. These Terms are written in English, and the English version controls.

20. Contact

© 2026 Journey On