My current research interests centre on understanding the behaviour of
**turbulent flows**.
Physically we all have a good understanding of what a turbulent flow
is. For example, white water rapids are clearly turbulent,
whereas a (stationary) jar of honey is not.
In fact, on the earth most flows, at most times, are turbulent.

[*Mathematically, one might say that a turbulent flow is
characterised by motions which occur over a broad range of length
(and time) scales and that these motions interact nonlinearly.
It is this nonlinear nature of the problem which makes it
simultaneously so rich and so challenging.
*]

A particular interest is **magnetofluid turbulence**, where the fluid is
**electrically conducting** so that one must consider not just the
behaviour of the fluid's velocity, but also that of its **magnetic field**.
Examples of
magnetofluids include liquid metals (e.g. mercury) and
plasmas (e.g. the sun, the solar wind, the working fluid in nuclear
fusion devices). Most of the matter in the universe is thought to be
in the plasma state, that is, the atoms have been ionised.

One way to study conducting fluids is using **magnetohydrodynamics
(MHD)**. This is the marriage of the equations of fluid dynamics with
those of electrodynamics, and provides a good approximation to the
behaviour of various parts of the solar system (or heliosphere).
Important dynamical features of MHD include waves, turbulence, plasma
heating, and particle acceleration.

The work involves a mixture of theory (including statistical mechanics and modeling) and computer simulations of the governing equations.

Vorticity movie (vorticity is a measure of the local rate of rotation of the plasma).

Electric current density movie.

Note how **vortices** with the same sense of rotation tend to
**``collide'' and merge**,
leading to a smoothing of the vorticity. The merger
process often involves a larger **vortex shredding** a smaller one which
is wrapped around the larger one and eventually absorbed into it.
In the current density movie the **dominant structures** are seen to be
much more **sheet-like** than in the case of the vorticity. In the
heliosphere, similar (but more intense) ``current sheets'' are sites
where particles are accelerated to relativistic energies and intense
heating of the plasma can occur.

There are also a couple of movies of this for the earlier times and for the later times.

[*Vorticity is a measure of the ``swirliness'' of a flow.
A vortex, such as the one over the plughole in an emptying bath,
has lots of vorticity,
whereas the water flowing straight out of a tap or a hose
doesn't have so much.
*]

This particular simulation took about 400 cpu-hours to complete on one of the fastest supercomputers available at the time (in the late 1980s). Today it could be done on a standard PC in well under a week!

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*Last modified: 14-Jan-2016.*