Near-field Flow Downstream of a Tidal Barrage: Experiments, 3-D CFD and Depth-averaged Modelling

1. Near-field Flow Downstream of a Tidal Barrage: Experiments, 3-D CFD and Depth-averaged Modelling Penny Jeffcoate Prof. P. K. Stansby & Dr. D. A. Apsley University of Manchester

2. 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 La Rance, France • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

3. Tidal Barrage Sites • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work • Large tidal range • Potential sites in UK: • Solway Firth • Morecambe Bay • Mersey • Dee • Severn • High initial investment • Environmental impact • Unknown flow effects

4. Project Motivation Previous Modelling Required Modelling • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work • 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)

5. 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

6. 1. How accurate is 2-D modelling? Experiments Scale factor = 1 in 143 D = 0.11m Uin = 0.1025 ms-1 hup = 0.2326m hdown = 0.2156m Weir Vectrino ADV Barrage ducts Barrage walls Inlet • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

7. 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

8. 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

9. Probe and Profile Locations 1D 5D 20D 2D 10D • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

10. StarCCM+ Velocity Vectors 1D 2D 5D 10D 20D • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

11. Depth-varying Velocity Profiles 1D 5D 20D • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

12. SW2D Velocity Vectors 1D 2D 5D 20D 10D • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

13. Depth-averaged Velocity Profile • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

14. Conclusions At 20D, 2-D modelling provides accurate flow representation, but until 20D 3-D results are more accurate • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

15. 2. Are the results affected by stator swirl? Experiments StarCCM+ Uin = 0.0784 ms-1 hup = 0.2326m hdown = 0.2154m Blades inclined at 30° • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work Bulb included in ducts Swirl generated by body force: Constant* [-x, -(z - zref), (y - yref)]

16. Velocity Vectors - Experimental 1D 5D 20D • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

17. Velocity Vectors - Experimental 4cm 12cm 18.5cm • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

18. Streamlines • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

19. Velocity Vectors - Computational • Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

20. 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

21. 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

22. Any Questions? Penny Jeffcoate penelope.jeffcoate@postgrad.manchester.ac.uk 0161 306 2614