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

Reaction — where it appears

A chemical change in the fluid that releases or absorbs energy and alters its composition. Whether it matters is decided by its own rate against the time the flow gives it, which is a residence time or a passage time rather than a temperature.

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

When the tracer leaves, given when it went in. The residence-time distribution of three beds with the same mean residence time and different Peclet numbers. Every one of them has its mean at exactly one, and they are nothing alike: the loosest lets a tenth of the tracer out before a third of the mean time has passed, and the tightest is nearly the spike a plug-flow calculation assumes.

The outlet is the inlet, a while ago

A bed has a mean residence time and everybody quotes it. Six beds with the same mean let their first hundredth through at 0.20 and at 0.85 of it, mix a window of inlet history between 1.53 and 0.18 wide, and convert a first-order reaction by amounts the mean cannot distinguish.

applied · Porous 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.

MeasurementMemory kernelAveragingBreakthroughCombustionConvolutionDetonationDispersionInduction timeInstabilityModel validityPeclet number

All concepts