Lord Rayleigh

Lord Rayleigh, born John William Strutt, was an English physicist whose 1916 analysis established a stability criterion for convection in a heated fluid layer.

Thermal convection: Heat transfer by the bulk movement of a fluid driven by temperature or density differences. Rayleigh’s stability problem asks when heating from below turns conduction into fluid motion.
Rayleigh–Bénard convection: A pattern of fluid circulation that arises when a fluid layer is heated from below and cooled from above. It is the canonical physical instability described by Rayleigh’s criterion.
John William Strutt, 3rd Baron Rayleigh: An English physicist whose work ranged across acoustics, optics, fluid mechanics, and electromagnetism. This is Rayleigh’s full name and broader scientific identity.
Mantle convection: The slow circulation of Earth’s mantle driven by internal heat and buoyancy. Rayleigh-number scaling helps characterize whether mantle heat transfer is conductive or convective.
Rayleigh number: A dimensionless measure comparing buoyancy-driven flow with viscous and thermal diffusion in a fluid. It condenses the layer’s competing forces into the parameter used in the stability criterion.
Linear stability analysis: A method that tests whether small disturbances to a system grow or decay. Rayleigh’s calculation identifies the parameter value at which infinitesimal disturbances stop decaying.
On Convection Currents in a Horizontal Layer of Fluid: Lord Rayleigh’s 1916 paper analyzing instability in a horizontal fluid layer heated from below. The paper gives the original analysis behind the stability criterion.
Atmospheric convection: Vertical atmospheric motion driven by buoyancy as air is heated or cooled. The same competition between buoyancy and diffusion helps frame atmospheric instability.
Boussinesq approximation: A fluid-flow approximation that treats density as constant except in the buoyancy force. It simplifies the equations for heated layers while retaining the density variation that drives convection.
Critical Rayleigh number: The threshold Rayleigh number at which a specified fluid layer first becomes unstable to convection. It expresses the onset condition derived from the layer’s geometry and boundary conditions.

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