penny jeffcoate prof. p. k. stansby & dr. d. a. apsley university of manchester near-field flow...
TRANSCRIPT
PENNY JEFFCOATE
P R O F. P. K . STA N SBY & D R . D. A . A P S L E Y
U N I V E R S I T Y O F M A N C H E S T E R
Near-field Flow Downstream of a Tidal Barrage:
Experiments, 3-D CFD and Depth-averaged Modelling
Presentation Outline
Introduction
Research Aims
Modelling Comparison Experimental, 3-D and depth-averaged modelling
Swirl Assessment Swirl with bulb and stators
Conclusions
Future Work Swirl with bulb, stators and propellers
Bed Shear stress and sediment transport
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
La Rance, France
Tidal Barrage Sites
Large tidal range
Potential sites in UK: Solway Firth
Morecambe Bay
Mersey
Dee
Severn
High initial investment
Environmental impact
Unknown flow effects
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Previous Modelling Required Modelling
2-D Depth-averaged
Large-scale 5-10m
Whole estuary
3-D Depth-variation
Small-scale 10-20cm
Immediately downstream of barrage 20 duct diameters (20D)
Project Motivation
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Research Aims
1. What is the limit of applicability of 2-D modelling at predicting close-to-barrage
flow?
2. Are the results affected by the incorporation of swirl?
3. How is the bed stress, and thus the sediment transport, affected?
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
1. How accurate is 2-D modelling?
Experiments Scale factor = 1 in 143D = 0.11m Uin = 0.1025 ms-1
hup = 0.2326mhdown = 0.2156m
Inlet
Barrage walls
Barrage ducts
WeirVectrino ADV
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
1. How accurate is 2-D modelling?
Three-Dimensional Modelling StarCCM+ - Upstream tank, ducts and downstream tank Unstructured polyhedral mesh Base cell size ~0.02m Boundary conditions
Velocity Inlet Pressure Outlet Walls Symmetry plane lid
Standard k-ε model Convergence criteria
Momentum and continuity
residuals 10-4
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
1. How accurate is 2-D modelling?
Two-Dimensional Modelling FORTRAN In-house Stansby SW2D model Downstream tank Cell size = ~0.01 – 0.02m Boundaries conditions
7 velocity inlets
Fixed depth boundary outlet
Vertical slip walls
2nd order, time-stepping model
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Probe and Profile Locations
20D
5D1D
10D
2D
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
StarCCM+ Velocity Vectors
2D
1D
5D
10D
20D
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Depth-varying Velocity Profiles
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
5D
20D
1D
SW2D Velocity Vectors
20D
5D
1D
10D
2D
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Depth-averaged Velocity Profile
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Conclusions
From 1 duct diameter (1D) to 10D downstream
At 20D downstream
Asymmetrical flow Symmetrical flow
Variation across depth No variation across depth
Large eddies in three-dimensional (3-D) model, small eddies in 2-D model
No eddies formed
Little similarity between 3-D and 2-D results
High compatibility between 3-D and 2-D results
At 20D, 2-D modelling provides accurate flow representation, but until 20D 3-D results are more
accurateIntroduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Experiments StarCCM+
Bulb included in ducts Swirl generated by body
force:Constant* [-x, -(z - zref), (y - yref)]
Uin = 0.0784 ms-1
hup = 0.2326mhdown = 0.2154m
Blades inclined at 30°
2. Are the results affected by stator swirl?
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Velocity Vectors - Experimental
1D
5D
20D
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Velocity Vectors - Experimental
4cm
12cm
18.5cm
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Streamlines
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Velocity Vectors - Computational
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Conclusions
What is the limit of applicability of 2-D modelling at predicting
close-to-barrage flow? Acceptable further downstream than 20 diameters
3-D modelling is required for close-to-barrage modelling
Are the results affected by the incorporation of swirl? Experimental results show large variations in flow and flow circulation
Amount of swirl in computation must be refined to match experiments
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
Future Work
Are the results affected by the incorporation of swirl? Altering the swirl constant
Comparison with experimental results
Incorporation of propeller
How is the bed shear, and thus sediment transport,
affected? Analysis of the close-to-bed experimental velocities
Comparison with computational results
Assessment of scour and deposition based on threshold of motion
Scaling assessment
Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work
