The Rankine vortex is a simple mathematical model of a
vortex
In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in ...
in a
viscous
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the in ...
fluid. It is named after its discoverer,
William John Macquorn Rankine
William John Macquorn Rankine (; 5 July 1820 – 24 December 1872) was a Scottish mechanical engineer who also contributed to civil engineering, physics and mathematics. He was a founding contributor, with Rudolf Clausius and William Thomson ( ...
.
The vortices observed in nature are usually modelled with an
irrotational (potential or free) vortex. However, in potential vortex, the velocity becomes infinite at the vortex center. In reality, very close to the origin, the motion resembles a solid body rotation. The Rankine vortex model assumes a solid-body rotation inside a cylinder of radius
and a potential vortex outside the cylinder. The radius
is referred to as the vortex-core radius. The velocity components
of the Rankine vortex, expressed in terms of the cylindrical-coordinate system
are given by
:
where
is the
circulation strength of the Rankine vortex. Since solid-body rotation is characterized by an azimuthal velocity
, where
is the constant
angular velocity
In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an object ...
, one can also use the parameter
to characterize the vortex.
The
vorticity field
associated with the Rankine vortex is
:
Inside the core of the Rankine vortex, the vorticity is constant and twice the angular velocity, whereas outside the core, the flow is irrotational. In reality, vortex cores are not always exactly circular; and vorticity is not uniform within the vortex core.
See also
*
Kaufmann (Scully) vortex – an alternative mathematical simplification for a vortex, with a smoother transition.
*
Lamb–Oseen vortex In fluid dynamics, the Lamb–Oseen vortex models a line vortex that decays due to viscosity. This vortex is named after Horace Lamb and Carl Wilhelm Oseen.
Mathematical description
Oseen looked for a solution for the Navier–Stokes equation ...
– the exact solution for a free vortex decaying due to viscosity.
*
Burgers vortex
External links
Streamlines vs. Trajectories in a Translating Rankine Vortex an example of a Rankine vortex imposed on a constant velocity field, with animation.
Notes
{{reflist
Equations of fluid dynamics
Vortices