News: PhD position on ‘Large-scale flow structures in shallow shear flows over rough bed‘
A PhD position will be opened at INRAE Lyon, from september 2021 to august 2024. The PhD is entitled ‘Large-scale flow structures in shallow shear flows over rough bed‘ . The experiments will be conducted in the wide flume of the HHLab (see below). The PhD student will be co-supervised by Dr S. Proust, C. Berni (INRAE), and Pr Vladimir Nikora from Aberdeen University.
- Position at : INRAE Lyon-Grenoble Centre, 5 rue de la Doua, 69100 Villeurbanne, France.
- From: Sept-Oct 2021 to: Aug. Sept 2024
- Title of the PhD: Large-scale flow structures in shallow shear flows over rough bed
- Profile of the candidate: strong background in fluid mechanics and/or hydraulics. The candidate must speak English (French can be learned during the PhD)
Co-supervisors: Sébastien Proust, Céline Berni (INRAE); Vladimir I. Nikora (University of Aberdeen)
Funding: INRAE Aqua department (50%) – UR Riverly (50%); PhD scholarship: 1498 euros per month (net)
Context: Shallow water flows can be encountered e.g., in rivers, lakes, and along the coastline. These flows can be sheared in the transverse direction when they are subject to topographical singularities (e.g. islands, dikes, river confluence, and two-stage channel) or to lateral changes in bed roughness. The shallow shear flows due to merging of two streams with different speeds can involve various types of Large-Scale Structures (LSSs) arising from the presence of the horizontal shearing and frictional effects of the channel bed and sidewalls. These LSSs can generally be classified as: (i) 2D large-scale horizontal vortices, termed Kelvin-Helmholtz-type Coherent Structures (KHCSs); (ii) 3D turbulent Large-Scale-Motions (LSMs); (iii) 3D turbulent Very-Large-Scale-Motions (VLSMs); and (iv) 3D streamwise time-averaged helical Secondary Currents (SCs). The effects of LSSs on rivers are multiple. First, the LSSs have been found to influence the flood hazards. For instance, in a compound open-channel, the absence or presence of KHCSs can substantially modify the stage-discharge relationship (e.g. Nicollet and Uan 1978, Bousmar 2002). Second, among the various types of LSSs, structures like SCs and KHCSs can be efficient for the lateral transfer of momentum (e.g. Proust & Nikora 2020 for compound channel flows; Vermaas et al. 2011 and Akutina et al. 2019 for flows subject to lateral roughness transitions) and for the mixing of pollutants, nutrients, sediments, and heat. For instance, at river confluences, the presence of large horizontal vortices (KHCSs) accelerates the mixing of sediments between streams as illustrated in Figure 1 (left), while without KHCSs two streams can coexist without mixing over noticeable distances (Figure 1, right). Structures like LSMs and VLSMs (Cameron et al. 2017) can play a predominant role in sediment transport (Cameron et al 2019; 2020) and mixing processes. Thus, to advance current capabilities to assess and predict flooding risks, mass/momentum transport and mixing, it is critically important to identify the predominant flow structures and to understand the interplay between them for a range of typical flow conditions and channel configurations.
Figure 1. (Left) Amazon River – Rio Negro confluence. (Right) Colorado River – Green River confluence.
Figure 2 : (left) Wide open-channel flume located in the HHLab. (right) Flow configurations that will be studied during the PhD
Methodology: Shallow shear flows will be studied in an 18 m long and 2 m wide open-channel flume (Figure 2 – left), which is located in the Hydraulics and Hydro-morphology Laboratory (HHLab) at INRAE, Lyon, France. Four bed configurations will be investigated (Figure 2 – right): (i) uniform bed roughness (bed is uniformly covered by dense artificial grass); (ii) bed with transverse change from smooth (glass) to rough (‘grass’) surfaces (half-width of the bed made of glass, half-width covered by artificial dense plastic ‘grass’); (iii) bed with transverse change from glass to emergent wooden circular cylinders installed on the glass bed; and (iv) bed with a lateral roughness change from plastic grass to emergent wooden circular cylinders installed on glass bed. The obtained hydraulic data will be compared to previous data sets collected in the HHLab for flows over smooth bed (Proust et al. 2020) and in compound channels (Proust & Nikora 2020). Regarding the measuring techniques, the three velocity components will be measured using two Acoustic Doppler Velocimeters with side-looking probes (including one- and two-point measurements). Spectra and two-point measurements will be analysed to identify the turbulent structures (Proust & Nikora 2020). Infra-red camera will be used to identify the initial emergence of KHCSs and heat transfer rates at the water surface. Temperature field will be analysed to quantify the mixing. Particle Image Velocimetry in a vertical-longitudinal plane will also be used to investigate the flow structure in the interfacial region between the two streams.
For further information: please contact lead supervisor Dr Sébastien Proust (email@example.com)
- Akutina, Y., O. Eiff, F. Moulin and M. Rouzes (2019). “Lateral bed‑roughness variation in shallow open‑channel flow with very low submergence.” Environmental Fluid Mechanics 19(5): 1339–1361.
- Bousmar, D. (2002). Flow modelling in compound channels / Momentum transfer between main channel and prismatic or non-prismatic floodplains Ph-D thesis, Université catholique de Louvain, Faculté des Sciences Appliquées.
- Nicollet, G. and M. Uan (1979). “Ecoulements permanents à surface libre en lit composés.” La Houille Blanche(1): 21-30.
- Cameron, S. M., V. I. Nikora and M. T. Stewart (2017). “Very-large-scale motions in rough-bed open-channel flow.” Journal of Fluid Mechanics 814: 416-429.
- Cameron, S. M., V. I. Nikora and M. J. Witz (2020).” Entrainment of sediment particles by very large-scale motions”. Journal of Fluid Mechanics 888, A7.
- Cameron, S. M., V. I. Nikora and I. Marusic (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.
- Proust, S., C. Berni and V. I. Nikora (2020). Emergence of Kelvin-Helmholtz instabilities in shallow mixing layers: An experimental study. River Flow 2020, 10th Conference on Fluvial Hydraulics. Delft, Netherlands, 7 to 10 July 2020.
- Proust, S. and V. I. Nikora (2020). “Compound open-channel flows: effects of transverse currents on the flow structure.” Journal of Fluid Mechanics 885(A24): 1-38.
- Vermaas, D. A., W. S. J. Uijttewaal and A. J. F. Hoitink (2011). “Lateral transfer of streamwise momentum caused by a roughness transition across a shallow channel.” Water Resources Research 47(W02530).
The Hydraulic and Hydromorphology Laboratory (HHLab) is a platform of 350 m² that includes three physical models (built and equipped from 2013 to 2017). This platform is dedicated to the study of physical processes associated with river flows or flows in a highly anthropized environment.
The three facilities are
- A wide flume, 3 m-wide, 18 m-long, 80 cm-deep, with a fixed bed slope of 1/1000.
- A tilting flume, 1 m-wide, 18 m-long, 80 cm-deep, with a maximum bed slope of 5 %.
- An urban flood model (MURI), 5.4 m-long, 3.8 m-wide, with maximum slopes of 5 % in the longitudinal and transverse directions.
Characteristics of the physical models
|Wide flume||Tilting flume||MURI|
|Total length||18 m||18 m||5.4 m|
|Width||3 m||1 m||3.8 m|
|Height||80 cm||80 cm||15 cm|
|Inlet conditions||3 independant inlet tanks||1 inlet tank||1 to 9 inlet tanks|
300 L.s-1 (75 L.s-1 + 150 L.s-1 + 75 L.s-1)
|150 L.s-1||50 L.s-1 to be shared between 1 to 9 inlets|
|Outlet conditions||3 adjustable tail weirs||1 adjustable tail weir||3 adjustable tail weirs+ 3 outlet tanks|
|Maximum bed slope||1/1000||5/100||5/100 in both directions|
Water and sediment supply
The two long flumes (wide and tilting) are supplied in in three different ways:
- Clean water can be supplied through a constant head water tower. The water is then recycled in a basement area.
- Sediment (diameter < 1 mm) laden water can also be supplied in a close loop. The water is recycled in another smaller basement area equipped with stirrer to homogenize the sediment concentration.
- Finally, it is possible to work in an open configuration for coarse sediment. The sediment settles in an intermediate tank. The flumes are fed in sediment independently of the water.
The scheme below illustrated these different modes:
Several sensors are deployed:
- Ultrasound sensors to measure free-surface elevation (9 sensors, 3 up-stream, 3 downstream, 3 mobile),
- Discharge measurements with an electromagnetic flowmeter at the entrance of the flume.
- Velocity measurements (Pitot tube, Acoustic Doppler Velocimeter, and PIV systems).
- Topographic measurements with a 2D laser scan (submillimetrical resolution, Scan-Control 2900-100)
These sensors are fixed to a motorized trolley and can be moved automatically.
We use these facilities to address multiple issues such as :
- vegetated flows
- shear flows (compound channels and mixing layers),
- transverse waves in stationary flows,
- urban floods,
- interactions between sediments of different sizes,
- alternated bars dynamics,
- unsteady flows
PhD and HdR Theses
- OUKACINE, M. – 2019. Étude expérimentale et numérique d’écoulements à surface libre en présence d’obstacles émergés et faiblement submergés. Thèse de doctorat, Mécaniques des fluides, Université de Paris Est. 231 p.
- PERRET, E. – 2017. Transport of moderately sorted gravels at low bed shear stresses: impact of bed arrangement and fine sediment infiltration. Thèse de doctorat, Mécaniques des fluides, Université de Lyon. 378 p.
- DUPUIS, V. – 2016. Experimental investigation of flows subjected to a longitudinal transition in hydraulic roughness in single and compound channels. Thèse de doctorat, spécialité : Mécanique des fluides, Université Lyon I Claude Bernard. 141 p.
- PROUST, S. – 2015. Steady non-uniform overbank flows in compound open-channels. Mémoire d’HDR, ED MEGA, Université Claude Bernard Lyon I.
- OUKACINE, M., PROUST, S., LARRARTE, F., GOUTAL, N. – 2021. Experimental flows through an array of emerged or slightly submerged square cylinders over a rough bed. Scientific Data , Nature Publishing Group, 8 (1), 10.1038/s41597-020-00791-w.
- CHATELAIN, M., PROUST, S. – 2020. Non-uniform flows in a compound open-channel: assessment of a hybrid RANS-LES approach. Water Resources Research, vol. 56, e2020WR027054. doi:10.1029/2020WR027054
- PROUST, S., NIKORA, V.I. – 2020. Compound open-channel flows: Effects of transverse currents on the flow structure. Journal of Fluid Mechanics, 885, A24. doi:10.1017/jfm.2019.973
- CHETIBI, M., PROUST, S., BENMAMAR, S. – 2020. Transverse surface waves in steady uniform and non-uniform flows through emergent and weakly submerged square cylinders. Journal of Hydraulic Research, vol. 58, n°4. DOI: 10.1080/00221686.2019.1647885
PERRET, E., BERNI, C., CAMENEN, B. – 2020. How does the bed surface impact low-magnitude bedload transport over gravel-bed rivers? Earth Surface Processes & Landform. doi: 10.1002/esp.4792
- PERRET, E., BERNI, C., CAMENEN, B., HERRERO, A., EL KADI ABDERREZZAK, K. – 2018. Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration. Earth Surface Processes and Landforms, vol. 43, n° 7, p. 1416-1430
- BERNI, C., PERRET, E., CAMENEN, B. – 2018. Characteristic time of sediment transport decrease in static armour formation. Geomorphology, vol. 317, p. 1-9
- PROUST, S., FERNANDES, J.N., LEAL, J.B., RIVIERE, N., PELTIER, Y. – 2017. Mixing layer and coherent structures in compound channel flows: effects of transverse flow, velocity ratio and vertical confinement . Water Resources Research, vol. 53, n° 4, p. 3387-3406.
- DUPUIS, V., PROUST, S., BERNI, C., PAQUIER, A. – 2017. Compound channel flow with a longitudinal transition in hydraulic roughness over the floodplains. Environmental Fluid Mechanics, vol. 17, n° 5, p. 903-928
- DUPUIS, V., PROUST, S., BERNI, C., PAQUIER, A. – 2017. Mixing layer development in compound channel flows with submerged and emergent rigid vegetation over the floodplains. Experiments in Fluids, vol. 58, n° 30, 18 p.
- HERRERO, A., BERNI, C. – 2016. Sand infiltration into a gravel bed: a mathematical model. Water Resources Research, vol. 52, 14 p.
- DUPUIS, V., PROUST, S., BERNI, C., PAQUIER, A. – 2016. Combined effects of bed friction and emergent cylinder drag in open channel flow. Environmental Fluid Mechanics, vol. 16, n° 6, p. 1173-1193