This repository contains the raw HTML of all articles hosted on cfd.university

Having all articles on GitHub allows for collaborative improvements of articles. If you have found issues, inconsistencies, or errors with the articles, please feel free to open up a new issue.

Articles on cfd.university are pulled weekly (Tuesday at 8am GMT) from this repository, at which the cache will be flushed and rebuilt as well. Critical changes can be pushed quicker, but will require me to do that manually.

Contribution guideline

Depending on how comfortable you feel with git/GitHub and raw HTML, you can either:

1. Fork this repository and make changes directly to the raw HTML and submit a pull request.
2. Open an issue and state what needs fixing/changing. I can then make those changes myself. In this case, you don't need to touch the HTML yourself.

Spelling rules

Use British English for all spelling/corrections, but feel free to ignore the following spellings (because I am proudly inconsistent):

• metre -> meter
• centre -> center
• aeroplane -> airplane
• aerofoil -> airfoil

Article structure

cfd.university was born on WordPress. WordPress does annotate the HTML and so you will find a lot of comments that have no influence now, as the website is now running using Python + Flask + Docker + 💛.

Any changes made should continue to use this styling for consistency (though I have no plan to go back to WordPress. I'm glad I left that mess behind).

Text changes

Text changes should be pretty straightforward. Edit the text you need. If you need a new paragraph, enclose it in a <p> tag as:

<!-- wp:paragraph -->
<p>Your paragraph goes here</p>
<!-- /wp:paragraph -->

Keep the WordPress paragraph comments as well. Each paragraph cannot have more than 550 characters (excluding the <p></p> tags and comments).

Equations

All equations displayed on cfd.university use standard LaTeX syntax. If you need to change equations inside a paragraph, make sure that you enclose an equation with [katex] and [/katex]. For example, you may have a text passage like:

Newton's second law states [katex]\mathbf{F}=m\mathbf{a}[/katex], from which we can derive the momentum equation.

If you want to make sure your equation is free of syntax errors, you can type it on katex directly and see how they render.

The [katex] and [/katex] tags are a left-over from WordPress. WordPress would scan each article before displaying it and convert all text inside these tags into equations using KaTeX, an online equation-rendering service. I have replicated that functionality, so old HTML articles will render correctly. Therefore, we need to use this non-standard HTML syntax.

If you want to place the equation on a new line, you can enclose it with a div:

<!-- wp:katex/display-block -->
<div class="wp-block-katex-display-block katex-eq" data-katex-display="true"><pre>\mathbf{F}=m\mathbf{a}</pre></div>
<!-- /wp:katex/display-block -->

The div and pre tags need to be present, with the same classes and attributes. Internally, these will then be rendered with katex again.

Here are a few rules I use when typing equations to make them consistent:

• Scalars use a normal font face, vectors and matrices use a bold font face. As we can see in the example above, the force F and acceleration a are vectors, and so they get a bold font face using the \mathbf{} syntax (math bold face). The mass m is a scalar and is written without any styling.
• If you use parentheses, start and end them with a leading \left and trailing \right identifier. This ensures parentheses automatically scale to the correct size. For example, \left( \frac{1}{2} \right). Since we are using a fraction here, the standard parentheses () would be too small, \left and \right scale them to the size of the fraction.
• When working with multiline equations, I almost always append a [1em] to the line break command, i.e. \\[1em]. This gives just a bit of breathing room, especially when fractions are involved. I only deviate from that if the equations are rather compact. If in doubt, end a line in \\[1em]. The exception here is matrices, for which I usually always just use a simple line break of \\.
• When working with differentials (mostly in integrals, e.g. dx in an integral like int(x)dx), the differential is never italic but always straight. So, a differential is not dx but always \mathrm{d}x, where \mathrm{} removes (math rm) the math styling. It works the same way as \text{d}x, but I prefer the math version, i.e. \mathrm{}.

Code

I am currently moving from legacy WordPress code listings to Python + Pygments-based code listings. Making changes to existing code listings is dangerous, as it may break formatting and style.

For the moment, the best option is to open a new issue if there are issues with the code, which I can then manually change. Eventually, all code snippets will be replaced by the Python + Pygments-based workflow.

Eventually, this will be all replaced, and code snippets will be converted in standard markdown syntax to HTML. I am using the MDLicious2 Markdown to HTML converter, and you can interactively convert Markdown text to HTML using the HTML preview on cfd.university.

Section headings

Section headings can be modified, but only to correct typos. Articles sometimes link to specific sections, so changing the link text would have adverse consequences. Don't change link text, even if they have typos. I can do that manually if need be.

Acknowledgement

Credit where credit is due! If you help to improve the articles, you will be listed in the acknowledgement section, which automatically appears once contributors exist.

If you prepare a pull request, please also change the metadata in the description.json file for that series/blog. For example, if you make changes to the first article in the 07_10-key-concepts-everyone-must-understand-in-cfd series, then modify the description.json file in 07_10-key-concepts-everyone-must-understand-in-cfd/description.json. Look for the article you have modified, for the first article, that would be:

"01_how-to-derive-the-navier-stokes-equations-from-start-to-end.html": {
    "heading": "How to Derive the Navier-Stokes Equations: From start to end",
    "slug": "how-to-derive-the-navier-stokes-equations",
    "description": "If you want to know how to derive the Navier-Stokes equations, look no further; this article derives them from start to end, with explanations and no omissions!"
},

You will have to add a new entry called contributions, which is a key value map (dictionary), where the key is your name (that will show up on the website) and the value is a link to your social media, personal website, etc. (try to avoid your OnlyFans account if possible). An example is shown below:

"01_how-to-derive-the-navier-stokes-equations-from-start-to-end.html": {
    "heading": "How to Derive the Navier-Stokes Equations: From start to end",
    "slug": "how-to-derive-the-navier-stokes-equations",
    "description": "If you want to know how to derive the Navier-Stokes equations, look no further; this article derives them from start to end, with explanations and no omissions!",
    "contributors": {
        "Tom-Robin Teschner": "https://github.com/tomrobin-teschner"
    }
},

If someone already contributed, simply add your name to the list:

"01_how-to-derive-the-navier-stokes-equations-from-start-to-end.html": {
    "heading": "How to Derive the Navier-Stokes Equations: From start to end",
    "slug": "how-to-derive-the-navier-stokes-equations",
    "description": "If you want to know how to derive the Navier-Stokes equations, look no further; this article derives them from start to end, with explanations and no omissions!",
    "contributors": {
        "Tom-Robin Teschner": "https://github.com/tomrobin-teschner",
        "Milo Edwards": "https://www.youtube.com/@milo_edwards"
    }
},

Keep in mind this is json, don't forget to add commas where necessary. If in doubt, throw the entire description.json file into a JSON validation tool like jsonlint and see if it is valid before submitting a pull request. But if you can do a pull request, you probably know how to handle JSON. Apologies for insulting your intelligence...

By default, I will use your full name (please provide that with a pull request or issue) and link to your github page unless you tell me you do not want to be mentioned in the acknowledgement section.