Too much of a good thing? Destabilisation and mixing induced by stratification in shear flows

By Dr Colm-cille Caulfield
BP Institute & DAMTP – University of Cambridge


Tuesday 27th of May 2014 – 14:00 / Room ME B3 31



Statically stable fluids, where the fluid density decreases monotonically with height, are very common in the environment, and arise due to the natural tendency for stationary fluid to be arranged in a state which minimises the potential energy of the system. It is then natural to suppose  that such a statically stable density distribution will reduce the growth rate and ultimate nonlinear saturated amplitude of instabilities associated with some large scale vertical shear of the fluid, compared to the properties of such instabilities in an unstratified fluid.  However, stratification  not only can introduce  primary instabilities of stratified shear flows which do not arise in the absence of density variations, but can also strongly modify the secondary instabilities which subsequently develop, modulating, and in some circumstances significantly accelerating the transition to turbulence. In this talk, I will review some aspects of the present understanding of the destabilising effect of statically stable stratification in shear flows, and discuss the central part such destabilisation plays in the commonly observed non-monotonic dependence of turbulent mixing on overall stratification, leading, through a classical physical mechanism first identified by Phillips, to the inevitable development of layers in stratified fluids.



1987: BSc (1st Class Hons) Mathematics, University of Ulster at Coleraine
1988: MASt Mathematics, University of Cambridge
1992: PhD, Fluid Dynamics, Department of Applied Mathematics & Theoretical Physics, University of Cambridge
1992-1994: Post-doctoral research fellow for the Japan-Canada Project in Weather and Climate of the Arctic, Department of Physics, University of Toronto
1995-1999: Lecturer, Department of Mathematics, University of Bristol
1999-2005: Assistant Professor then Associate Professor of Environmental Engineering, Department of Mechanical and Aerospace Engineering, Irwin and Joan Jacobs School of Engineering, University of California, San Diego
2005-: University Lecturer, then University Senior Lecturer in Fluid Flow, then Reader in Environmental and Industrial Fluid Dynamics,  BP Institute and the Department of Applied Mathematics and Theoretical Physics, University of Cambridge
2005-: Fellow and College Lecturer in Mathematics, Churchill College, University of Cambridge


Dr Colm-cille Caulfield holds a joint appointment in the Department of Applied Mathematics and Theoretical Physics and the BP Institute at the University of Cambridge. The BP Institute is a multi-disciplinary research centre devoted to fundamental studies of problems related to the energy industry, defined in the broadest sense. It brings together industrialists and academics with expertise in applied mathematics, earth sciences, engineering and chemistry.

Dr Caulfield is interested in working as part of such diverse teams to study various fluid flows in the environment, particularly in cases where density differences play a dynamical role. Of course, density differences, (due to temperature or composition variation) are ubiquitous in the environment. Understanding the fundamental properties of the associated fluid dynamics is key to ensuring sustainable human activity. To name just three important examples, understanding how density differences affect fluid flows can allow strategies to be developed to model the climate system, to deal with the dispersion of pollutants, or to minimise energy consumption within buildings.


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