Vladimir Nikora, Stuart Cameron, Dubravka Pokrajac, Tom O'Donoghue, Mark Stewart, Yukie Tanino, Zaibin Lin
Open-channel flow (OCF) is free-surface flow driven by gravity and contained within channel boundaries. The key differences between OCFs and other types of wall-bounded flows (Figure 1) include: (1) unlike the boundary layer thickness which always increases along the flow, OCF depth may decrease or increase or stay the same along the flow; (2) corners at the intersections of the channel walls, bed, and free-surface of OCFs induce turbulence anisotropy that in turn leads to generation of secondary currents (in very wide channels the secondary currents may weaken or even die out away from the channel walls); and (3) the free surface acts as a mobile moving boundary that may have significant impact on the whole flow dynamics. Altogether, these features make OCF a special class of wall-bounded turbulent flows distinctly different from boundary layers as well as from conduits and pipes where the free surface is absent.
Figure 1. Types of wall-bounded turbulent flows
Examples of open-cannel flows include rivers and artificial channels (canals) with complex (non-straight) plan forms, irregular cross-sections, and mobile sedimentary boundaries. These features induce additional dynamic effects that may not be easily accommodated with simple parameterizations and theoretical descriptions. Our work in this Research Area is therefore focused on (1) theoretical approaches for rough-bed OCFs, particularly development of the double-averaging methodology; (2) OCF turbulence, including both coherent and random features of velocity fields; (3) bed friction and overall hydraulic resistance in OCFs; (4) flow-sediment interactions; (5) flow-biota interactions; and (6) development of advanced instrumentation such as world-first multi-camera robotic Particle Image Velocimetry (PIV) system for laboratory studies (Figure 2) and Stereoscopic Field PIV system for experiments in rivers and canals (Figure 3).
Figure 2. World-first robotic Particle Image Velocimetry System developed by the Group is used in laboratory studies of flow dynamics, sediment transport and flow-biota interactions; the system’s unique features include flexibility to measure velocity fields at multiple locations and at various spatial scales, from roughness to depth scales.
Figure 3. In-situ study of river turbulence in the Urie River (Scotland) using world-first advanced Field Particle Image Velocimetry System developed by the Group.
Recent External Projects
| 2021-2024 | Secondary currents in turbulent flows over rough walls, EPSRC, UK (V. Nikora, S. Cameron, £735K), part of a collaborative program with the University of Southampton, University College London, and University of Glasgow. |
| 2020-2023 | RIver flow regulation, fish BEhaviour and Status (RIBES), EC, Marie Skłodowska-Curie Innovative Training Networks H2020-MSCA-ITN-2019 (V. Nikora, S. Cameron, B. Scott, S. Martin, €305K), a part of a collaborative international research program led by the Politecnico Di Torino. |
| 2019-2020 | Field stereoscopic particle image velocimetry (FSPIV) system for high-resolution in-situ studies of freshwater and marine ecosystems, NERC, UK (S. Cameron, £289k) |
| 2014-2018 | Bed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantification, EPSRC, UK (V. Nikora, S. Cameron, £526.5k), part of a collaborative program with the Cardiff University |
| 2013-2016 | Hydrodynamic transport in ecologically critical heterogeneous interfaces (HYTECH), EC, Marie Curie Initial Training Networks FP7-PEOPLE-2012-ITN (V. Nikora, S. Cameron, C. Gibbins, €597K), a part of a collaborative international research program led by the University of Padova. |
| 2010-2014 | High resolution numerical and experimental studies of turbulence-induced sediment erosion and near-bed transport, EPSRC, UK (V. Nikora, S. Cameron, £493k), part of a collaborative program with Universities of Karlsruhe and Dresden, funded by DFG |
Recent PhD projects
| 2021 | Dr Wada Patella | Hydraulic resistance, secondary currents and free surface fluctuations in open-channel flows with streamwise ridges |
| 2019 | Dr Andrea Zampiron | Hydraulic resistance and flow structure in open-channel flow over streamwise ridges |
| 2017 | Dr Mario Savio | Turbulent structure and transport processes in open-channel flows with patchy-vegetated beds |
| 2017 | Dr Shaun Fraser | Acoustic investigation of the hydrodynamics and ecology of a tidal channel and the impacts of a marine renewable energy installation |
| 2017 | Dr Hamish Biggs | Flow-vegetation interactions from the plant to the patch mosaic scale |
| 2017 | Dr Konstantinos Papadopoulos | Theoretical frameworks for the upscaling of physical interactions in aquatic mobile-boundary flows |
| 2016 | Dr Davide Vettori | Hydrodynamic performance of seaweed farms: an experimental study at seaweed blade scale |
| 2015 | Dr Nina Nikora | Flow structure and hydraulic resistance in channels with vegetated beds |
| 2015 | Dr Matthew Witz | Mechanics of particle entrainment in turbulent open-channel flows |
| 2015 | Dr Steffen Gretland | Hydrodynamics of fishing gear at twine and mesh scales: an experimental study |
| 2014 | Dr Mark Stewart | Turbulence structure of rough-bed open-channel flow |
| 2012 | Dr Fabio Siniscalchi | Hydrodynamics of flow-vegetation interactions at the scales of individual plant and plant patch |
Selected papers
- Zampiron, A., Cameron, S., Stewart, M., Marusic, I., Nikora, V. (2022). Flow development in rough-bed open channels: mean velocities, turbulence statistics, velocity spectra, and secondary currents. Journal of Hydraulic Research, 61(1), 133-144.
- Proust, S., Berni, C., Nikora, V. (2022) Shallow mixing layers over hydraulically smooth bottom in a tilted open channel. Journal of Fluid Mechanics, 951, A17.
- Zampiron, A., Cameron, S., Nikora, V. (2021) Momentum and energy transfer in open-channel flow over streamwise ridges. Journal of Fluid Mechanics, 915, A42
- Cameron, S., Nikora, V., Witz, M. (2020) Entrainment of sediment particles by very-large-scale motions. Journal of Fluid Mechanics, 888, A7.
- Zampiron, A., Cameron, S., Nikora, V. (2020) Secondary currents and very-large-scale motions in open channel flow over streamwise ridges. Journal of Fluid Mechanics, 887, A17.
- Proust, S., Nikora, V. (2020) Compound open-channel flows: effects of transverse currents on the flow structure. Journal of Fluid Mechanics, 885, A24.
- Zampiron, A., Nikora, V., Cameron, S., Patella, W., Valentini, I., Stewart, M. (2020) Effects of streamwise ridges on hydraulic resistance in open-channel flows. Journal of Hydraulic Engineering, 146(1).
- Papadopoulos, K., Nikora, V., Cameron, S., Stewart, M., Gibbins, C. (2020) Spatially averaged flows over mobile rough beds: Equations for the second-order velocity moments. Journal of Hydraulic Research, 58(1), 133-151.
- Papadopoulos, K., Nikora, V, Vowinckel, B., Cameron, S., Jain, R., Stewart, M., Gibbins, C., Fröhlich, J. (2019) Double-averaged kinetic energy budgets in flows over mobile granular beds: insights from DNS data analysis. Journal of Hydraulic Research.
- Nikora, V., Stoesser, T., Cameron, S., Stewart, M., Papadopoulos, K., Ouro, P., McSherry, R., Zampiron, A., Marusic, I., Falconer, R. (2019) Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows. Journal of Fluid Mechanics, 872, 626-664.
- Biggs, H.J., Nikora, V.I., Gibbins, C.N., Cameron, S.M., Papadopoulos, K., Stewart, M., Fraser, S., Vettori, D., Savio, M., O’Hare, M.T., Kucher, M., Hicks, D.M. (2019) Flow interactions with an aquatic macrophyte: a field study using stereoscopic Particle Image Velocimetry (PIV). Journal of Ecohydraulics, 4(2), 113-130.
- Cameron, S., Nikora, V., Marusic. I. (2019) Drag forces on a bed particle in open-channel flow: Effects of pressure spatial fluctuations and very large scale motions. Journal of Fluid Mechanics, 863, 494-512.
- Witz, M., Cameron, S., Nikora, V. (2019) Bed particle dynamics at entrainment. Journal of Hydraulic Research, 57(4), 464-474,
- Stewart, M., Cameron, S., Nikora, V., Zampiron, A., Marusic, I. (2019) Hydraulic resistance in open-channel flows over self-affine rough beds. Journal of Hydraulic Research, 57(2), 183-196.
- Pokrajac, D., Venuleo, S., Franca, M.J. (2018) Depth-averaged momentum equation for gravity currents with varying density: coefficient in pressure term. Journal of Hydraulic Research, 56(3), 424-430.
- Mathur, A., Gorji, S., He, S., Seddighi, M., Vardy, A.E., O'Donoghue, T. (2018) Temporal acceleration of a turbulent channel flow. Journal of Fluid Mechanics, 835, 471-490.
- Vowinckel, B., Nikora, V., Kempe, T. Fröhlich, J. (2017) Spatially-averaged momentum fluxes and stresses in flows over mobile granular beds: a DNS-based study. Journal of Hydraulic Research, 55(2), 208-223.
- Vowinckel, B., Nikora, V., Kempe, T. Fröhlich, J. (2017) Momentum balance in flows over mobile granular beds: application of double-averaging methodology to DNS data. Journal of Hydraulic Research, 55(2), 190-207.
- Cameron, S.M., Nikora, V., Stewart, M.T. (2017) Very-large-scale motions in rough-bed open-channel flow. Journal of Fluid Mechanics, 814, 416-429.
- Amir, M., Nikora, V., Witz, M. (2017) A novel experimental technique and its application to study the effects of particle density and flow submergence on bed particle saltation. Journal of Hydraulic Research, 55 (1), 101-113.
- Seddighi, M., He, S., Pokrajac, D., O'Donoghue, T., Vardy, A.E. (2015). Turbulence in a transient channel flow with a wall of pyramid roughness. Journal of Fluid Mechanics, 781, 226-260.
- Mohajeri, S.H., Grizzi, S., Righetti, M., Romano, G.P., Nikora, V. (2015) The structure of gravel-bed flow with intermediate submergence: a laboratory study. Water Resources Research, DOI: 10.1002/2015WR017272.
- Amir, M., Nikora, V., Stewart, M. Pressure forces on sediment particles in turbulent open-channel flow: a laboratory study. (2014) Journal of Fluid Mechanics, 757, 458-497.
- Nikora, V., Ballio, F., Coleman, S.E., Pokrajac, D. (2013) Spatially-averaged flows over mobile rough beds: definitions, averaging theorems, and conservation equations. Journal of Hydraulic Engineering, ASCE, 139(8), 803-811.
- Katul, G.G., Porporato, A., Nikora, V. (2012) Existence of the k-1 power-law scaling in the equilibrium regions of wall-bounded turbulence explained by Heisenberg's eddy viscosity. Physical Review E, 86(6-2).