Fields
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.
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.
Circulation and lift
Where lift actually comes from. The Kutta condition, the Joukowski aerofoil, and lift derived rather than asserted.
Viscosity
The thin layer next to a surface that ideal flow ignores, and which supplies drag, separation and the wake.
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.
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.
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.
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.
What is taught wrongly
Equal transit time, Bernoulli misapplied, and the rest. Each stated fairly, then tested against a solved flow and found false.
Other ways through
a field is one of five
A field says what an essay is about. It is the coarsest of the five organisations this site carries, and the other four cut across it. A series groups essays by the idea they make an argument about, so a series is depth on one idea rather than breadth across a subject. Threads are the motifs that recur in places with no business being related. Regimes sort every figure on the site by the hypothesis it states — the Reynolds or Mach number the result depends on — which is the organising axis of fluid mechanics and of nothing else here. Refutations collect every wrong explanation this site tests, with the computation that settles each one.