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Very large scale motions (VLSM) in rough-bed turbulent open-channel flows: topology, statistics, dynamics


School of Engineering

About the Project

Turbulence in open-channel flows such as rivers and canals plays a key role in transport of momentum, sediments, nutrients, and other substances. Thus, the knowledge of the turbulence structure is required for making predictions and assessments relevant to water management.

The structural approach in turbulence research and its concept of coherent structures have emerged from the recognition of some order in turbulent flows that may exhibit highly organized motions. A coherent structure (or motion) can be broadly defined as a persistent three-dimensional flow region over which at least one fundamental flow variable exhibits significant correlation with itself or with another variable over a range of space and/or time.

Based on extensive experimental studies, the following classification of coherent structures in hydraulically-smooth wall-bounded flows has been proposed (e.g., Marusic & Adrian, 2013): (1) quasi-streamwise vortices, residing within the viscous and buffer sublayers; (2) hairpin vortices, ‘growing’ from the solid surface and scaled with the distance from the bed; (3) large-scale motions which are epitomized by hairpin packets reaching 2 to 4 flow depths; and (4) very-large scale motions (or superstructures), the diameter of which is comparable to flow depth H while their length may reach up to 50H. A similar classification should also be applicable for rough-bed flows, with the exception of the smallest structures which are associated with wake eddies behind roughness elements rather than with quasi-streamwise vortices as in smooth-bed flows.

The objective of this PhD is to advance the classification of coherent structures for rough-bed open-channel flows particularly focusing on very-large scale motions VLSM (or superstructures) which are the least studied motions in open-channel flows. The project focus will be on the identification of VLSMs, their statistics, and dynamics. The key project methodology is experimental, involving experiments in a large flume and Particle Image Velocimetry.

Candidates should have (or expect to achieve) a UK honours degree at 2.1 or above (or equivalent) in Mechanical Engineering or Civil Engineering or Aerospace Engineering or Physics.

Essential background: Fluid Mechanics, Open-Channel Hydraulics, Turbulence, Roughness effects, Sediment Transport.

Knowledge of: Engineering Mathematics, Fluid Mechanics (with focus on turbulence), Hydraulics, Statistical methods, Programming, Water engineering, Numerical methods.

APPLICATION PROCEDURE:

• Apply for Degree of Doctor of Philosophy in Engineering
• State name of the lead supervisor as the Name of Proposed Supervisor
• State ‘Self-funded’ as Intended Source of Funding
• State the exact project title on the application form

When applying please ensure all required documents are attached:

• All degree certificates and transcripts (Undergraduate AND Postgraduate MSc-officially translated into English where necessary)
• Detailed CV

Informal inquiries can be made to Prof V Nikora (), with a copy of your curriculum vitae and cover letter. All general enquiries should be directed to the Postgraduate Research School ()

Funding Notes

This project is advertised in relation to the research areas of the discipline of Engineering. The successful applicant will be expected to provide the funding for Tuition fees, living expenses and maintenance. Additional research costs totalling £5,000 - £7,000 may be required. Details of the cost of study can be found by visiting View Website. THERE IS NO FUNDING ATTACHED TO THIS PROJECT

References

Cameron, S.M., Nikora, V.I. and Witz, M.J., (2020). Entrainment of sediment particles by very large-scale motions. J. Fluid Mech., 888.
Cameron, S.M., Nikora, V.I. and Marusic, I., (2019). Drag forces on a bed particle in open-channel flow: effects of pressure spatial fluctuations and very-large-scale motions. J. Fluid Mech., 863, pp.494-512.
Cameron, S.M., Nikora, V.I. and Stewart, M.T., (2017). Very-large-scale motions in rough-bed open-channel flow. J. Fluid Mech., 814, pp.416-429.
Smits, A.J. & Marusic, I. (2013) Wall-bounded turbulence. Phys. Today, 66, 25-30.
Adrian, R.J., & Marusic, I. (2012) Coherent structures in flow over hydraulic engineering surfaces. J. Hydraulic Res, 50, 451-464.
Marusic, I. & Adrian, R.A. (2012) Eddies and scales of wall turbulence. In Ten Chapters in Turbulence (ed. P.A. Davidson, Y. Kaneda and K.R. Sreenivasan). Cambridge University Press, Cambridge.
Smits, A.J., McKeon, B.J., & Marusic, I. (2011) High Reynolds number wall turbulence. Ann. Rev. Fluid Mech. 43, 353-375.
Marusic, I., McKeon, B.J., Monkewitz, P.A., Nagib, H.M., Smits, A.J., & Sreenivasan, K.R. (2010) Wall-bounded turbulent flows at high Reynolds numbers: Recent advances and key issues. Phys. Fluids 22, 065103, 1-24.
Monty, J.P., Hutchins, N., Ng, H.C.H., Marusic, I. and Chong, M.S. (2009) A comparison of turbulent pipe, channel and boundary layer flows. J. Fluid Mech. 632, 431-442.
Hutchins, N. & Marusic, I. (2007) Evidence of very long meandering structures in the logarithmic region of turbulent boundary layers. J. Fluid Mech. 579, 1-28.

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