Burgers vortex
In fluid dynamics, the Burgers vortex or Burgers–Rott vortex is an exact solution to the Navier–Stokes equations governing viscous flow, named after Jan Burgers[1] and Nicholas Rott.
[2] The Burgers vortex describes a stationary, self-similar flow.
An inward, radial flow, tends to concentrate vorticity in a narrow column around the symmetry axis, while an axial stretching causes the vorticity to increase.
At the same time, viscous diffusion tends to spread the vorticity.
The stationary Burgers vortex arises when the three effects are in balance.
The Burgers vortex, apart from serving as an illustration of the vortex stretching mechanism, may describe such flows as tornados, where the vorticity is provided by continuous convection-driven vortex stretching.
The flow for the Burgers vortex is described in cylindrical
so that at infinity the solution behaves like a potential vortex, but at finite location, the flow is rotational.
The solution is The vorticity equation only gives a non-trivial component in the
-direction, given by Intuitively the flow can be understood by looking at the three terms in the vorticity equation for
, The first term on the right-hand side of the above equation corresponds to vortex stretching which intensifies the vorticity of the vortex core due to the axial-velocity component
The intensified vorticity tries to diffuse outwards radially due to the second term on the right-hand side, but is prevented by radial vorticity convection due to
The three-way balance establishes a steady solution.
The Burgers vortex is a stable solution of the Navier–Stokes equations.
[4] One of the important property of the Burgers vortex that was shown by Jan Burgers is that the total viscous dissipation rate
per unit axial length is independent of the viscosity, indicating that dissipation by the Burgers vortex is non-zero even in the limit
For this reason, it serves as a suitable candidate in modelling and understanding stretched-vortex tubes observed in turbulent flows.
The total dissipation rate per unit axial length is, in incompressible flows, simply equal to the total enstrophy per unit length, which is given by[5] An exact solution of the time dependent Navier Stokes equations for arbitrary function
, an arbitrary vorticity distribution approaches the Burgers' vortex.
, say in the case where the initial condition is composed of two equal and opposite vortices, then the first term is zero and the second term implies that vorticity decays to zero as
This is also an exact solution of the Navier–Stokes equations, first described by Albert A. Townsend in 1951.
-direction, given by The Burgers vortex sheet is shown to be unstable to small disturbances by K. N. Beronov and S. Kida[9] thereby undergoing Kelvin–Helmholtz instability initially, followed by second instabilities[10][11] and possibly transitioning to Kerr–Dold vortices at moderately large Reynolds numbers, but becoming turbulent at large Reynolds numbers.
[12] The structure of non-axisymmetric Burgers' vortices for arbitrary values of vortex Reynolds number can be discussed through numerical integrations.
[13] The velocity field takes the form subjected to the condition
plane, providing a non-zero vorticity component in the
direction The axisymmetric Burgers' vortex is recovered when
Explicit solution of the Navier–Stokes equations for the Burgers vortex in stretched cylindrical stagnation surfaces was solved by P. Rajamanickam and A. D.
[14] The solution is expressed in the cylindrical coordinate system as follows where
is the radial location of the cylindrical stagnation surface,
Explicit solution for Sullivan vortex in cylindrical stagnation surface also exists.
