Professor Chris Keylock

I am interested in a range of non-linear and complex phenomena and ways of analysing such systems. At the heart of contemporary interests is the role of non-locality and non-equilibrium phenomena in the dynamics of turbulent flows. Turbulence has been described as the last great problem in classical physics and the regularity of the Navier-Stokes equations is a Clay Millenium problem, highlighting some of the technical difficulties. However, even small developments in this area have profound practical implications. 

Broadly associated work involves the development of synthetic data for formulating null hypotheses for the study of complex phenomena. These have been applied to financial, geomorphological, hydrological and turbulence data. 

If there is an unique dimension to my work, it is perhaps the statistical and physics-based perspective I bring to bear on rather mathematical topics. As such, I have made some contributions to intermittency science and multifractal methods using wavelet techniques, as well as applied matrix analysis methods. I am interested in using the latter to develop new closure models for turbulence, for use in applied computational fluid dynamics.

Recently completed research projects

• Traditional analyses of the velocity gradient tensor in turbulence are either based on the additive decomposition into strain and rotation, or based on the eigenvalues. We extended the latter to incorporate non-normal parts of the tensor and then undertook the strain and rotation decomposition to discover new terms in the fundamental equations. This work was published in Journal of Fluid Mechanics.
• We have shown that there is an unique velocity-intermittency structure to canopy turbulence that seems to hold for atmospheric and hydrodynamic cases (work with Duke, MIT and Western Australia) and was published in Environmental Fluid Mechanics.
• We have shown that the amplitude modulation of boundary-layer can be written in terms of a coupling between Hölder exponents and the large scale velocity variation (work with Southampton and Melbourne). This work was published in Fluid Dynamics Research and won the 10th Fluid Dynamics Research Prize.

Fluid Mechanics

• Beaumard, P., Buxton, O.R.H., Keylock, C.J. (2019) The importance of non-normal contributions to velocity gradient tensor dynamics for spatially developing, inhomogeneous, turbulent flows, Journal of Turbulence 10.1080/14685248.2019.1685095.
• Keylock, C.J. (2019) Turbulence at the Lee bound: maximally non-normal vortex filaments and the decay of a local dissipation rate, Journal of Fluid Mechanics 881, 283-312, 10.1017/jfm.2019.779.
• Keylock, C.J. (2018) The Schur decomposition of the velocity gradient tensor for turbulent flows, Journal of Fluid Mechanics 848, 876-904, 10.1017/jfm.2018.344.
• Keylock, C.J. (2017) Synthetic velocity gradient tensors and the identification of significant aspects of the structure of turbulence, Physical Review Fluids2, 8, 084607, 10.1103/PhysRevFluids.2.084607.
• Keylock, C.J., Chang, K.S., Constantinescu, G.S. (2016) Large eddy simulation of the velocity-intermittency structure for flow over a field of symmetric dunes, Journal of Fluid Mechanics 805, 656-685. 
• Higham, J., Brevis, W., Keylock, C.J. (2016) A rapid non-iterative proper orthogonal decomposition-based outlier detection and correction method for PIV data, Measurement Science and Technology 27, no. 125303, doi: 10.1088/0957-0233/27/12/125303.
• Keylock, C.J., Ganapathisubramani, B., Monty, J., Hutchins, N. and Marusic, I. (2016) The coupling between inner and outer scales in a zero pressure boundary-layer evaluated using a Hölder exponent framework, Fluid Dynamics Research 48, 2, 021405. 
• Keylock, C.J., Stresing, R. and Peinke, J. (2015) Gradual wavelet reconstruction of the velocity increments for turbulent wakes, Physics of Fluids 27, 025104.

Nonlinear Data Processing

• Keylock, C.J. (2019) Hypothesis testing for nonlinear phenomena in the geosciences using synthetic, surrogate data, Earth and Space Science 6, doi: 10.1029/2018EA000435
• Keylock, C.J. (2018) Gradual multifractal reconstruction of time-series: Formulation of the method and an application to the coupling between stock market indices and their Hölder exponents, Physica D 368, 1-9.
• Keylock, C.J. (2017) Multifractal surrogate-data generation algorithm that preserves pointwise Hölder regularity structure, with initial applications to turbulence, Physical Review E 95, 032123, 10.1103/PhysRevE.95.032123.

Hydrodynamics

• Keylock, C.J., Ghisalberti, M., Katul, G.G., Nepf, H.M. (2020) A joint velocity鈥慽ntermittency analysis reveals similarity in the vertical structure of atmospheric and hydrospheric canopy turbulence, Environmental Fluid Mechanics 20, 77-101, 10.1007/s10652-019-09694-w.
• Kesserwani, G., Shaw, J., Sharifian, M.K., Bau, D., Keylock, C.J., Bates, P.D., Ryan, J.K. (2019) (Multi)wavelets increase both accuracy and efficiency of standard Godunov-type hydrodynamic models, Advances in Water Resources 129, 31-55, 10.1016/j.advwatres.2019.04.019
• Higham, J., Brevis, W., Keylock, C.J. (2018) Implications of the selection of a particular modal decomposition technique for the analysis of shallow flows, Journal of Hydraulic Research 56(6), 796-805.
• Higham, J.E., Brevis, W., Keylock, C.J., Safarzadeh, A. (2017) Using modal decompositions to explain the sudden expansion of the mixing layer in the wake of a groyne in a shallow flow, Advances in Water Resources 107, 451-459.
• Keylock, C.J. (2015) Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics, Water Resources Research 51, 10.1002/2015WR016989.

Geomorphology

• Keylock, C.J., Singh, A., Passalacqua, P., Foufoula-Georgiou, E. (2020) Hölder鈥怌onditioned Hypsometry: A Refinement to a Classical Approach for the Characterization of Topography, Water Resources Research, doi: 10.1029/2019WR025412
  

Undergraduate

• CVA105: Mechanical and Mathematical Principles of Fluid Mechanics
• CVC04: Water Engineering

Postgraduate

Following undergraduate and Masters’ studies at the universities of Oxford and British Columbia, I spent much of 1997 working on avalanche risk assessment for the Icelandic Meteorological Office. I took up the offer of a NERC-funded Ph.D. in Cambridge in 1997 and obtained my first lecturing position at Leeds in 2000. Having gone part-time at Leeds for child-care reasons from 2007-2010, I moved on to a Prize Senior Lectureship at Sheffield in 2010. In 2016/17 I obtained a Royal Academy of Engineering / Leverhulme Trust Senior Research Fellowship that I spent with Charles Meneveau in Mechanical Engineering at Johns Hopkins and the Turbulence and Mixing Group in Aeronautics at Imperial College. I joined 含羞草视频 in 2018 as Professor of Fluid Mechanics.

My research interests have evolved over this period from work on snow avalanche dynamics and risk assessment, through fluvial geomorphology to turbulence physics and the development of methods for nonlinear science. The following are specific pieces of work of possible note in approximate chronological order:

• Development of a statistical risk analysis framework for avalanche hazards;
• Development of wavelet-based methods for creating synthetic data for hypothesis testing. In particular, the gradual wavelet reconstruction and gradual multifractal reconstruction philosophies;
• Helped develop an advanced radar for imaging the dynamics of snow avalanches, which is now installed at the Vallée de la Sionne test-site in Switzerland;
• Proposed the velocity-intermittency quadrant method for obtaining information on flow structures in turbulent flows from single point information;
• Proposal to analyse the velocity gradient tensor of turbulence having first decomposed it into normal and non-normal parts using a Schur decomposition.

The latter forms the primary focus of my current work. Much of this work has been undertaken in collaboration with some fantastic colleagues from around the world.

Professional affiliations

• American Geophysical Union

Awards

• The Tenth Fluid Dynamics Research Prize 2017, awarded by the Japanese Society for Fluid Mechanics

External activities

• I have been Associate Editor for Water Resources Researchsince 2013.
• In 2016 I edited a special issue of Fluid Dynamics Research on Interscale Transfers and Flow Topology in Equilibrium and Non-Equilibrium Turbulence.
• In 2010 I edited a special issue of Progress in Physical Geographyon The Future of Geomorphology.

Key collaborators

My research and enterprise activities are conducted with a range of academic partners, including but by no means limited to:

• Fluid Mechanics:
  Bharath Ganapathisubramani, Engineering, Southampton; Ivan Marusic, Mechanical Engineering, Melbourne; Joachim Peinke, Physics, Oldenburg; The Turbulence and Mixing Group, Aeronautics, Imperial College. 
• Geomorphology:
  Efi Foufoula, Civil Engineering, UC Irvine; Stuart Lane, Geosciences, Lausanne; Arvind Singh, Civil Engineering, Central Florida  
• Hydrodynamics:
  George Constantinescu, Civil Engineering, Iowa; Heidi Nepf, Civil Engineering, MIT; Kouichi Nishimura, Environment, Nagoya.
• Snow avalanches:
  Massi Barbolini, Hydraulic Engineering, Pavia; Paul Brennan, Electrical Engineering, UCL; Nicolas Eckert, IRSTEA, Grenoble; Jim McElwaine, Planetary Science Institute, Arizona; Betty Sovilla, SLF, Davos.