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PENNY JEFFCOATE PROF. P. K. STANSBY & DR. D. A. APSLEY UNIVERSITY OF MANCHESTER Near-field Flow Downstream of a Tidal Barrage: Experiments, 3-D CFD and Depth-averaged Modelling

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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

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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

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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

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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

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1. How accurate is 2-D modelling? Experiments Scale factor = 1 in 143 D = 0.11m U in = ms -1 h up = m h down = m Inlet Barrage walls Barrage ducts Weir Vectrino ADV Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

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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 Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

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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 2 nd order, time-stepping model Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

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

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

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

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

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

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Conclusions From 1 duct diameter (1D) to 10D downstream At 20D downstream Asymmetrical flowSymmetrical flow Variation across depthNo 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 Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

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Experiments StarCCM+ Bulb included in ducts Swirl generated by body force: Constant* [-x, -(z - z ref ), (y - y ref )] U in = ms -1 h up = m h down = m Blades inclined at 30° 2. Are the results affected by stator swirl? Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

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

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

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Streamlines Introduction – Research Aims – Modelling – Swirl – Conclusion – Future Work

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

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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

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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

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Bed Shear Stress Introduction – Research Aims – Modelling – Swirl – Bed Stress - Conclusion

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Shields Parameter Introduction – Research Aims – Modelling – Swirl – Bed Stress - Conclusion

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PENNY JEFFCOATE Any Questions?

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