Dr. Buxton is always looking for high quality PhD students. Please feel free to contact him to discuss research projects but note that this will typically require the student to obtain their own source of funding. A good tool for this purpose is the Imperial College London scholarship search tool but please note that he is currently supervising a President's Scholarship student and so is currently ineligible to take another. Where funding is available for a a specific PhD position it will be advertised on Dr. Buxton's LinkedIn page.
Fine scale turbulence
Richard Fenynman described turbulence as the "most important unsolved problem of classical physics". It is inherently multi-scale with the finest scales, responsible for the dissipation of kinetic energy of the flow, often being predicted numerically as being "universal". This "universality" can be observed through the interaction between the strain-rate and the rotation on a fine-scale level across a variety of turbulent flows.
State of the art laser diagnostics now make it possilbe to produce fully three-dimensional data that is sufficiently well spatially ressolved to observe these fine-scale phenomena. The aim of this research is thus to scrutinise the assumption of the "universality" of fine-scale turbulence.
Turbulent flows, e.g. volcanic plumes, are observed to grow with downstream distance. This is due to the transport and mixing of background fluid into the turbulent bulk across the sharp interface demarcating the turbulent flow from the background. This process is known as entrainment and has been studied from the special context of entrainment into a turbulent flow from a non-turbulent background since the 1950s. However, most environmental and industrial flows exist within a background that is itself turbulent, e.g. a wind farm exists within the turbulent atmospheric boundary layer.
The turbulent nature of the background flow fundamentally alters the physics of this entrainment, relative to the special case of turbulent/non-turbulent entrainment. We are now investigating these flow physics, both from a fundamental perspective and also from the perspective of modelling how they affect the spreading rate of wind-turbine wakes since this will affect the optimal layout of a wind farm to maximise the power output whilst minimising fatigue damage to the wind-turbine components. Tackling this particular problem is the subject of my recent EPSRC fellowship.
Many flows in nature are generated at multiple length and time scales simultaneously, for example the flow through a city is affected by buildings ranging from the size of a skyscraper to a house. Such multiscale-generated turbulent flows have extremely interesting properties, for example forest fires (where trees/branches of all different sizes co-exist) propagate extremely rapidly.
We are unpacking these rich multiscale physics from a fundamental perspective and have discovered exotic phenomena such as a reverse cascade of kinetic energy, i.e. from small scales to larger scales. In addition we are examining applications for these physics, such as mixing (which is an industrially inefficient process) as well as near-wake modelling of wind turbines. Wind turbines are inherently multiscale since forcing is introduced simultaneously by the blades, nacelle, tower etc.
Scale interactions in a self-preserving turbulent free shear flow, University of Southampton, Southampton, UK, 2014
Scale interactions in a free turbulent shear flow and the kinematics of the reduced velocity gradient tensor, Technical University of Delft, Delft, Netherlands, 2014
An academic life post Osborne Reynolds, University College London, London, UK, 2014
Fine-scale features in turbulent shear flow, Department of Aerospace Engineering, The University of Texas at Austin, Austin, Texas, USA, 2011
The fine scale features of turbulent shear flow, Instituto Superior Tecnico, Lisbon, Portugal, 2010
The fine scale features of turbulent shear flows, Instituto Superior Técnico, Lisbon, Portugal, 2010