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

PENNY JEFFCOATE

PENELOPE.JEFFCOATE@POSTGRAD.MANCHESTER.AC.UK0161 306 2614

Any Questions?