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The defining equations for viscosity are not fundamental laws of nature, so their usefulness, as well as methods for measuring or calculating the viscosity, must be established using separate means. A potential issue is that viscosity depends, in principle, on the full microscopic state of the fluid, which encompasses the positions and momenta ...
(dynamic) viscosity (also ) pascal second (Pa⋅s) theta: angular displacement: radian (rad) kappa: torsion coefficient also called torsion constant newton meter per radian (N⋅m/rad) lambda: cosmological constant: per second squared (s −2)
Poiseuille equation · Pascal's law; Viscosity ... (no standard symbol) ... The Cambridge Handbook of Physics Formulas. Cambridge University Press.
This coefficient of proportionality is called volume viscosity. Common symbols for volume viscosity are and . Volume viscosity appears in the classic Navier-Stokes equation if it is written for compressible fluid, as described in most books on general hydrodynamics [6] [1] and acoustics. [9] [10]
The Stokeslet is the Green's function of the Stokes-Flow-Equations. The conservative term is equal to the dipole gradient field. The formula of vorticity is analogous to the Biot–Savart law in electromagnetism. Alternatively, in a more compact way, one can formulate the velocity field as follows:
The poise (symbol P; / p ɔɪ z, p w ɑː z /) is the unit of dynamic viscosity (absolute viscosity) in the centimetre–gram–second system of units (CGS). [1] It is named after Jean Léonard Marie Poiseuille (see Hagen–Poiseuille equation). The centipoise (1 cP = 0.01 P) is more commonly used than the poise itself.
The three viscosity equations now coalesce to a single viscosity equation = = because a nondimensional scaling is used for the entire viscosity equation. The standard nondimensionality reasoning goes like this: Creating nondimensional variables (with subscript D) by scaling gives
A simple and widespread empirical correlation for liquid viscosity is a two-parameter exponential: = / This equation was first proposed in 1913, and is commonly known as the Andrade equation (named after British physicist Edward Andrade). It accurately describes many liquids over a range of temperatures.