Multiphase flow from a civil engineering perspective Benjamin Dewals, Sébastien Erpicum, Pierre Archambeau & Michel Pirotton HECE – Hydraulics in Environmental and Civil Engineering University of Liege www.hece.ulg.ac.be
University of Liege Founded in 1817 All faculties, 20,000 students Department ArGEnCo Architecture, Geology, Environmental and Civil Engineering 250 staff members, 30 academics APPLIED Research ENVIRONMENTAL HYDRODYNAMICS HYDRAULICS group AND HYDRAULIC CONSTRUCTIONS Benjamin Dewals HECE Michel Pirotton Associate Professor Full Professor HYDROLOGY, LABORATORY OF FREE SURFACE AND ENGINEERING PRESSURIZED FLOW HYDRAULICS Pierre Archambeau Sébastien Erpicum Research Associate Laboratory manager
The modelling system WOLF, developed by the team, enables to study a wide range of flows in civil engineering WOLF HYDRO WOLF WOLF 2D / 3D 1D Channel networks Detailed flow analysis Rainfall-runoff • Turbulence modelling modelling • Non-hydrostatic features • Bottom curvature Transport of air, www.hece.ulg.ac.be Clear water sediments, pollutant, … Self-developed pre- and post-processing user interface
Composite modelling enhances both understanding of basic processes and performance of numerical models Main test slab Test slabs 1100 m² Storage tank 400 m³ Regulated pumps 400 l/s www.hece.ulg.ac.be 3 (tilting) flumes up to 20 m long Workshops (synthetic materials, wood, steel, concrete) Pumps room
Three main types of multiphase flow are commonly addressed in civil engineering Aerated flow on hydraulic structures e.g., on spillways and in pipes Sediment transport e.g., reservoir sedimentation, flushing www.hece.ulg.ac.be Debris flow, geophysical granular flow e.g., waste dump failure
The type of weir crest significantly influences the location of the inception point on a stepped spillway Piano Key Piano Key E.g., Riou dam, France Ogee-crest IAHR Media library Weir 1 Weir 2 Experimental facility at our laboratory www.hece.ulg.ac.be
Air-water interactions alter the flow dynamics and hence the discharge capacity in bottom outlets of dams Example: design of the bottom outlet of a dam b. View of the physical model www.hece.ulg.ac.be 1:30 scale model 3D view of a typical bottom outlet gallery
Between smooth stratified flow and pressurized flow, intermediate flow show distinct multiphase characteristics 0,8 0,8 0,8 W a t e r F l o w Pure water fully pressurized flow Pure water fully pressurized flow Pure water fully pressurized flow 0.7 0.7 0.7 Bubbly flow Bubbly flow Bubbly flow W a t e r F l o w With air vent With air vent With air vent 0.53 0.53 0.53 Classic Classic Without air vent Without air vent Without air vent Intermittent flow: Plug/Slug flow Intermittent flow: Plug/Slug flow Intermittent flow: Plug/Slug flow Preissmann Preissmann W a t e r F l o w 0.4 0.4 0.4 Interval of variation Wavy stratified flow Wavy stratified flow Wavy stratified flow Negative Preissmann Water Flow 0.3 0.3 0.3 Smooth stratified flow Smooth stratified flow Smooth stratified flow Instability Upstream Upstream Upstream Kerger et al. Adv. Eng. Soft. (2011) Water Flow pressure pressure pressure head [m] head [m] head [m] Upstream reservoir bottom level Upstream reservoir bottom level Upstream reservoir bottom level 0,0 0,0 0,0 www.hece.ulg.ac.be Flow discharge [l/s] Flow discharge [l/s] Flow discharge [l/s] 5 50 5 5 50 50 Numerical result obtained from a 1D Homogeneous Equilibrium model Air-water interactions alter the discharge capacity of the bottom outlet
Modelling the failure of waste dumps lies at the frontier between geotechnical and hydraulic engineering Jupille, near Liege (1961) Run out of ~ 200,000 t Fly ash dump www.hece.ulg.ac.be Mining tip collapse in England (1967)
Modelling the failure of waste dumps lies at the frontier between geotechnical and hydraulic engineering Jupille, near Liege (1961) Material: fly ashes Run out of ~ 200,000 t over ~ 700 m Fly ash dump Physical properties: = 1000 – 1400 kg/m³ Lateral dikes d 50 = 40 µm in the deposits Quasi-static mechanical characteristics: = 20 700m www.hece.ulg.ac.be 10m deep Topography: deposits Steep-sided valley ~ 20 – 30 Mild-sloped thalweg ~ 3
Three main types of multiphase flow are commonly addressed in civil engineering Aerated flow on hydraulic structures e.g., on spillways and in pipes Sediment transport e.g., reservoir sedimentation, flushing ► Basic research, with practical applications in mind … www.hece.ulg.ac.be Debris flow, geophysical granular flow e.g., waste dump failure
Reservoir sedimentation: a worldwide challenge Volume worldwide ( billion m³) 6000 Total storage worldwide Net storage capacity 4000 2000 Sedimentation worldwide 0 0 1900 1950 2000 ICOLD (2009) 1-2% of worldwide storage capacity is lost every year! World bank: “ Last century was used to build reservoirs. This one will be used to solve sediment problems ...”
Complexity in morphodynamic modelling stems from the multiscale processes in space and time Multiscale in space Multiple processes Mutliscale in time • Bed load • Suspended load Soil erosion • Sediment exchange on the watershed Reservoir • Bank failures sedimentation: within • ... years or decades 1 to 10 5 km² Reservoir sedimentation 1 to 10 3 m 10 to 10 3 km Bank failures: within Flushing operations planned during seconds! www.hece.ulg.ac.be hours, days or weeks differences of up to Transport in rivers 9 orders of magnitude!
Morphodynamic modelling system enabling four levels of coupling between sub-models Synchronous Sequential Stochastic Iterative process resolution resolution particle tracking Next time step Next time step Next iteration Next time step Flow sub-model Flow sub-model Flow sub-model Flow sub-model (unsteady, 1 step) (unsteady, 1 step) ► steady state ► steady state Sediment transport Sediment transport Sediment transport Sediment transport + morphodynamics only + morphodynamics + morphodynamics (unsteady, 1 step) (unsteady, 1 step) (unsteady, 1 step) (steady approach) Increasing relative time scale of morphological changes ~ 10 0 s ~ 10 1 -10 3 s ~ 10 4 -10 8 s → ∞ www.hece.ulg.ac.be Bank failure Flushing Sedimentation Maintenance
Shallow rectangular reservoirs Flow pattern Sedimentation pattern • Experimental observations • Experimental observations • Numerical prediction • Example of practical implication • Theoretical stability analysis • Morphodynamic modelling www.hece.ulg.ac.be Feedback from sedimentation on flow pattern
Physical modelling L max = 7 m Water depth = 20 cm Velocity at inlet = 0.28 m/s Inlet channel width = 0.3 m Basin width = 1 m www.hach.ulg.ac.be Dufresne, Dewals et al. (2010)
Flow pattern classification L L 6 . 2 6 . 8 0 . 60 0 . 40 0 . 60 0 . 40 B B b B b B Q b L www.hach.ulg.ac.be Dufresne, Dewals et al. (2010)
Shallow rectangular reservoirs Flow pattern Sedimentation pattern • Experimental observations • Experimental observations • Numerical prediction • Example of practical implication • Theoretical stability analysis • Morphodynamic modelling www.hece.ulg.ac.be Feedback from sedimentation on flow pattern
Can those flow patterns be predicted by a 2DH flow model? Shallow-water equations (WOLF 2D) No disturbance at inflow Finite volume scheme: • 2 nd order accurate • self-developed FVS Eddy viscosity: • algebraic model: T = h u * • two-length-scale k - model Bottom and wall friction Slight disturbance at inflow (1%) www.hach.ulg.ac.be Observed flow field Dewals, Kantoush et al. (2008) Dufresne, Dewals et al. (2011)
All flow patterns well reproduced, based on a seed for asymmetry ”Short” reservoirs Intermediate length S0 pattern A1 pattern ”Long” reservoirs A2 pattern www.hach.ulg.ac.be Dufresne, Dewals et al. (2011)
Co-existence of two stable flow patterns depending on flow history Symmetric IC Symmetric IC Deviated IC Deviated IC www.hach.ulg.ac.be Dufresne, Dewals et al. (2011)
Shallow rectangular reservoirs Flow pattern Sedimentation pattern • Experimental observations • Experimental observations • Numerical prediction • Example of practical implication • Theoretical stability analysis • Morphodynamic modelling www.hece.ulg.ac.be Feedback from sedimentation on flow pattern
Flow pattern strongly influences trapping efficiency as can be deduced from experimental data and numerical simulations Observed location of deposits Observed deposits patterns Dufresne, Dewals et al. (2011) Kantoush (2008), PhD thesis, EPFL 0 1 2 3 4 5 6 7 m m m m m m m m Experiment ST1-a 0 m 1 m 2 m 0 m 1 m ▲ Material = Granular plastic (Styrolux 656 C) s = 1.020 d 50 = 2.5 mm w s = 25 mm/s C in = 0.5 g/l Mainly bedload Material = walnut shell s = 1.5 d 50 = 50 m w s = 1 mm/s C in = 3.0 g/l Mostly suspended load
Sudden rise in trapping efficiency as flow bifurcates from S0 to A1 www.hece.ulg.ac.be
Sudden rise in trapping efficiency as flow bifurcates from S0 to A1 TE = Trapping efficiency TE ~ 50% Global TE ~ 65% i.e. increase by almost 1/3 for a similar spatial extent! www.hece.ulg.ac.be 1 – TE ~ 70% ▲ BUT if S0 flow pattern, 70% ▲ Global TE < 15-20% !! 1 – TE ~ 70% 70% ▲ 1 – TE ~ 70% 70%
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