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

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  • Full or part time
    Prof V Nikora
    Dr S Cameron
  • Application Deadline
    Applications accepted all year round
  • Self-Funded PhD Students Only
    Self-Funded PhD Students Only

Project Description

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 and maintenance of water ecosystems.

The objective of this PhD is to advance the classification of turbulent 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.

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.

The successful candidate should have, or expect to have, an 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.

Funding Notes

This project is for self-funded students only. There is no funding attached to this project. The successful applicant will be expected to pay Tuition Fees and living expenses, from their own resources, for the duration of study.

References


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.
Nikora, V., & Roy, A.G. Secondary flows in rivers: theoretical framework, recent advances, and current challenges. In Gravel Bed Rivers: Processes, Tools, Environments, edited by M. Church, P.M. Biron, and A.G. Roy, London, Wiley and Sons, 2012, 3-22.

APPLICATION PROCEDURE:

This project is advertised in relation to the research undertaken in Engineering. Formal applications can be completed online: http://www.abdn.ac.uk/postgraduate/apply. You should apply for Degree of Doctor of Philosophy in Engineering, to ensure that your application is passed to the correct College for processing.

NOTE CLEARLY THE NAME OF THE SUPERVISOR AND EXACT PROJECT TITLE YOU WISH TO BE CONSIDERED FOR ON THE APPLICATION FORM. Applicants are limited to applying for a maximum of 2 projects. Any further applications received will be automatically withdrawn.

Informal inquiries can be made to Prof V Nikora ([email protected]) with a copy of your curriculum vitae and cover letter. All general enquiries should be directed to the Graduate School Admissions Unit ([email protected]).

How good is research at Aberdeen University in General Engineering?

FTE Category A staff submitted: 38.60

Research output data provided by the Research Excellence Framework (REF)

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