Fluid Flow & Aerodynamics
why things fly, and why the usual explanation is wrong
Concept

Induction time — where it appears

The delay between a mixture reaching conditions at which it can react and the reaction actually taking off. It falls exponentially with temperature, so an ignition threshold quoted as a temperature is really the long-hold limit of a curve in temperature and time.

Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.

A threshold that is a curve, not a pressure. The tension a rectangular pulse has to reach to make a five-micron bubble run away, against how long the pulse lasts. At a tenth of a microsecond it takes forty bar; at a hundred microseconds it takes 1.05, which is within about one per cent of the static threshold. There is no such thing as the cavitation pressure of this bubble on its own.

A threshold that is also a duration

The cavitation number treats inception as a pressure: below it the liquid tears, above it does not. A five-micron bubble asked to grow in 0.3 microseconds needs 43 bar of tension and the same bubble given a hundred needs 1.05, because it has to make a journey and not merely respond.

applied · Cavitation The structure the sensitivity produces. A detonation front, schematically: a leading shock, an induction zone in which nothing measurable happens, and a reaction zone behind it. The induction zone's length is set by the shock's own strength, and because that dependence is exponential the front is unstable and breaks into cells.

A gas that has not decided to react yet

Behind a detonation's leading shock there is a zone in which nothing measurable happens. Its length is set by the temperature the shock produced, exponentially — a one per cent change in the shock shortens it by fifteen per cent — and that sensitivity is why a detonation front cannot stay flat.

compressible · Detonation

Named alongside it

The objects these essays reach for when they reach for this one.

Memory kernelModel validityBubble dynamicsCavitationCombustionDetonationInertiaInstabilityMeasurementNucleationReactionRegime

All concepts