Chairs
Dr Colm-cille Caulfield, University of Cambridge, UK
Dr Colm-cille Caulfield, University of Cambridge, UK
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.
09:05-09:40
Stratified turbulent mixing in the ocean: patterns, processes, and parameterisation
Dr Jennifer MacKinnon, University of California San Diego, Scripps Institution of Oceanography, USA
Abstract
Though average observed diapycnal mixing rates in the ocean interior are consistent with values required by inverse models, recent focus has been on the dramatic spatial variability of mixing rates in both the upper and deep ocean, which spans several orders of magnitude. Global ocean models have been shown to be very sensitive not only to the overall level but to the detailed distribution of mixing. Some of these patterns are driven by the geography of generation, propagation and destruction of internal waves, which are thought to supply much of the power for turbulence in the ocean interior. I will briefly review some results from the last five years of a Climate Process Team tasked with improving representations of internal-wave driven mixing in the oceanic component of climate models. Another set of recent and ongoing work has turned to the poorly understood role of mesoscale and sub-mesoscale features in stratified oceanic turbulence. In some situations, the interplay between internal waves and mesoscale vorticity can noticeably enhance turbulent mixing rates. In other situations, sub-mesoscale instabilities act to re-stratify the ocean, a counter-balance of sorts to one-dimensional vertical mixing schemes. Recent observational examples of both situations will be presented, and discussed in the broader framework of global mixing rates.
Show speakers
Dr Jennifer MacKinnon, University of California San Diego, Scripps Institution of Oceanography, USA
Dr Jennifer MacKinnon, University of California San Diego, Scripps Institution of Oceanography, USA
Jennifer MacKinnon studies small-scale dynamical processes in the ocean, primarily internal waves and turbulence. Her main interests lie in integrating ocean observations, process studies and numerical simulations to understand the dynamics of high-frequency ocean processes and their relationship to lower-frequency global phenomena. MacKinnon has been involved with numerical process studies of nonlinear interactions between internal waves, with ocean-going observations of internal-wave driven turbulent mixing, and has recently become interested in sub-mesosacle instabilities as observed in the upper ocean. Simultaneously, MacKinnon is working with collaborators to use numerical and observational results to develop analytical parameterisations of turbulent diffusivity for use in large-scale climate models.
09:40-10:20
Mixing in density-stratified, free shear flows and the implications for mixing in the ocean
Professor Greg Ivey, University of Western Australia, Australia
Abstract
To first order, in the interior of the ocean the mean density and horizontal velocity fields can be considered a function of the vertical coordinate z. For this simple shearing flow, we introduce a new mixing length model to describe the mixing of density and momentum. We introduce a mixing length Lp controlling mixing in the density field and a mixing length Lm controlling mixing in the momentum field. There are no undetermined coefficients in the model, and no need to make any assumptions about the value of the flux Richardson number Rif. The model determines Rif and demonstrates Rif is dependent on the relative magnitudes of three length scales: Lp, Lo, and Ls , where Lo is the Ozmidov scale and Ls the Corrsin shear scale. The model predictions are in good agreement with published laboratory observations. We discuss the implications of the model for the interpretation of oceanic turbulent microstructure measurements and the description of mixing in numerical ocean models.
Show speakers
Professor Greg Ivey, University of Western Australia, Australia
Professor Greg Ivey, University of Western Australia, Australia
Greg Ivey is a member of the School of Civil, Environmental and Mining Engineering and the Oceans Institute at University of Western Australia (UWA). Greg has a BE and a MEng Science from UWA, and a PhD from the University of California at Berkeley. His research interests are in the area of physical oceanography, with particular focus on ocean turbulence and mixing, internal wave dynamics, and coastal ocean dynamics. In recent years his work has focused on observations at sea, mainly on the Australian North West Shelf (NWS). The NWS is density-stratified year-round, stirred by strong tidal currents and episodic tropical cyclones in the summer months. The research challenges of the region are both to undertake engineering developments, and to manage the unique marine ecosystems of the region.
10:50-11:30
Parameterising mixing in the stably stratified ocean interior
Dr Sonya Legg, Princeton University, USA
Abstract
Vertical mixing is suppressed in the stable density stratification of the ocean interior, yet the vertical turbulent diffusion of heat and salt still plays a significant role in the thermohaline circulation. Ocean climate models cannot explicitly resolve the mixing processes, so must employ parameterisations relating the mixing to resolved parameters. Such mixing requires a source of energy, supplied by sheared flow; when this shear is resolved, for example in large-scale ocean currents, the parameterised turbulent diffusion can be expressed in terms of the resolved flow and stratification. However, in much of the ocean, the shear responsible for mixing is due to internal waves, which are rarely simulated in climate models. These waves are generated by the tides and wind, propagate around the ocean, and eventually lead to mixing when they break. Parameterisation of the mixing due to breaking internal waves must account for the generation, propagation and dissipation of wave energy. High resolution simulations can be used to examine the mechanisms of wave breaking, extending understanding gained from observations. Here I will describe different internal wave breaking mechanisms, including nonlinear wave-wave interactions, wave reflection from sloping and shoaling topography, and transient hydraulic jumps, as well as recent efforts to combine this understanding into a global model of the tidally-driven internal wave energy budget leading to an energetically consistent parameterisation of mixing. The impact of different geographical distributions of wave-breaking on global ocean circulation will be demonstrated using coupled climate models.
Show speakers
Dr Sonya Legg, Princeton University, USA
Dr Sonya Legg, Princeton University, USA
Sonya Legg received her PhD from Imperial College London in 1993, and a Climate and Global Change postdoctoral fellowship from NOAA in 1995. Legg has been a member of the Princeton University Atmospheric and Oceanic Sciences programme faculty for 10 years, following several years at Woods Hole Oceanographic Institution. Legg is currently the lead PI for MPOWIR (Mentoring Physical Oceanography Women to Increase Retention), a nation-wide mentoring effort. Legg’s research interests focus on turbulent mixing in the ocean, including tidal mixing and mixing in overflows, the representation of mixing processes in large-scale ocean models, and the impact of parameterised small-scale mixing on the large-scale ocean circulation and climate. Legg has participated in two climate process teams, multi-institutional collaborations bringing together observationalists, modellers, and climate model developers, to better parameterise ocean processes.
11:30-12:10
Mixing processes in the oil and gas industry
Dr Simon Bittleston, Schlumberger Gould Research, UK
Abstract
Oil wells are very long and skinny (with aspect ratios of the order 10^5) and in many operations a tube sits within the wellbore with fluids pumped down the centre of this pipe, and back up the annulus between the pipe and rock. Flow rates vary significantly leading to some operations being performed in laminar flows, whilst others are turbulent. The fluids can be Newtonian or non-Newtonian. When the tube is not concentric in the wellbore, it is possible that laminar, transitional and turbulent flow can coexist in the annular space at any particular depth. The simplest case of dispersion of a tracer in a single phase flow is already of interest as the time evolution of fluid properties of the outlet of a well can give an indication of earlier events near the bottom. Taylor dispersion calculations show how sensitive the outlet distribution can be to eccentricity of the inner tube, and how rotation of the inner tube can counteract this. In some cases it is also useful to understand how a tracer distribution approaches the Taylor limit. As many of the fluids used are non-Newtonian, even these relatively simple cases exhibit unusual behaviours. More complex cases involve pumping a sequence of fluids of varying densities and rheological properties down through the tube and up the annular space. In these cases mixing process are complex, with a variety of instabilities possible. An approximate model system can be derived for certain geometrical configurations leading to realistic prediction of mixing processes. Laminar flow problems are already challenging; adding the complexity of turbulent, or partially turbulent flows, leads to a range of problems which deserve greater study. This talk will lead from the single phase to the multi-fluid and from the laminar to the turbulent, to explain the broad range of rich mixing processes that can occur in an important practical application.
Show speakers
Dr Simon Bittleston, Schlumberger Gould Research, UK
Dr Simon Bittleston, Schlumberger Gould Research, UK
Simon Bittleston is currently Vice President of Research for Schlumberger, a position he assumed in 2012. He is responsible for research centres in Boston, Cambridge (UK), Moscow, Rio, Stavanger, Edmonton, Houston and Dhahran, covering all aspects of oil-field activities.
Bittleston joined Schlumberger in 1985 and worked at Schlumberger Cambridge Research becoming a research programme manager. He moved to Norway in 1993 and became domain manager for the development of Marine Seismic systems where he was responsible for the development of Q-Marine. In 1999 he returned to the UK as a Research Director, and then in 2001 moved to Houston as VP Product Development which included all Product Development and Manufacturing for Schlumberger. In 2005 he moved to Paris and became VP of Mergers and Acquisitions – the team completed more than 40 investments.
Bittleston holds a Bachelor’s degree in mathematics from Imperial College London, and a PhD in fluid mechanics from the University of Bristol, UK. He is also a By-Fellow of Churchill College, Cambridge and Fellow of Darwin College, Cambridge.