Fluid Flow & Aerodynamics
why things fly, and why the usual explanation is wrong
How this site is made

The figure library

Every picture here is generated from code, and every flow field in it was solved and checked before it was drawn. This is the list of generators, grouped by the part of the subject they belong to, with how many essays call each — which is both the reuse this collection lives on and the blast radius of changing one.

No figure on this site is a drawing that was made once and saved. Each one is a function: it takes parameters and returns SVG, so the same generator produces the flow at Reynolds number 40 and at 400 without either being redrawn.

That is the reason the collection can keep growing without the illustrations drifting apart. A generator is written once, checked once, and every essay that calls it inherits the same line weights, the same colour roles, and the same behaviour in dark mode. There are 171 of them, and between them 724 essays call them 1064 times.

The count beside each name is how many essays instantiate it, because that number is the one worth watching. A generator written for a single essay and never called again is a design failure rather than a neutral cost: the whole economy of this collection is that a picture drawn for one argument turns out to be the picture for six. It is also the blast radius — changing a generator changes every figure on its page at once.

Each generator's page draws it at its defaults. What each essay asks for instead is on the regime index, which reads the parameters back out of the finished figures rather than out of the placements that made them.

Flows and fields

Streamlines, particle paths and the field that carries them. What is conserved, what a picture of a flow can show, and what it cannot. — 14 generators.

Ideal flow

The exact theory of a fluid with no viscosity — closed-form, elegant, and predicting no drag at all. Its failure is the most useful thing in the subject. — 16 generators.

Circulation and lift

Where lift actually comes from. The Kutta condition, the Joukowski aerofoil, and lift derived rather than assumed. — 27 generators.

Viscosity

The thin layer next to a surface that ideal flow ignores, and which supplies drag, separation and the wake. — 23 generators.

Regimes and numbers

Reynolds, Mach, Froude, Strouhal. One number decides whether a flow creeps, separates or shocks, and the same shape behaves differently at each. — 16 generators.

Compressible flow

What changes when density stops being a constant. Shocks, expansion fans, nozzles that work backwards, and the one place on this site where an inviscid flow has drag. — 17 generators.

Transition and turbulence

Where the laminar solutions stop being the ones the flow takes, and what can honestly be said about what follows — which is less than the textbooks imply and more than nothing. — 21 generators.

Fluids at work

Turbines, pipes, weirs, balls, sails, arteries and blades. What the conservation laws say about machines, which is more than a designer expects and less than a brochure claims. — 24 generators.

What is taught wrongly

Equal transit time, Bernoulli misapplied, and the rest. Each stated fairly, then tested against a solved flow and found false. — 13 generators.

All essays · The fields · The regime index