ICWES15 - Optimising Hydropower Generation through Fluid Dynamics Research. Presented by Dr Jessica...

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Optimising Hydropower Generation Through Fluid Dynamics Research

Dr Jessica Andrewartha*, Dr Jane Sargison, Xiao Lin LiSchool of Engineering, University of Tasmania, Australia

Presentation OverviewIntroduction

• Hydropower in Tasmania

• What is biofouling?

Efficiency Improvements in Hydropower Pipelines

Physics of Flow over Biofilms

• Real

• Artificial

Mitigation & Control

Summary & Conclusions

Repulse Dam, Derwent River, Tasmania

Faculty of Science, Engineering & Technology

Introduction

• Majority of electricity in Tasmania produced by 29 hydropower stations

• Potential for hydropower in Australia well exploited – now looking at efficiency improvements

• Hydropower stations require transport of water – sometimes over long distances (20 + km)

• Tunnels, canals, flumes, pipelines & penstocks – susceptible to biofouling

• UTAS / Hydro / ARC 10 year research collaboration on biofouling

Tarraleah Penstocks, Tasmania


Introduction

Biofouling is the undesirable growth of biological matter at liquid – solid interfaces

Global problem – causes large drag penalties

3 categories:• Low-form gelatinous (slimes)• Filamentous• Hard deposits

Natural biofilms consist of one or more components

www.crestock.com/image/131228-Barnacle-Texture.aspx



Why clean?• Remove biofouling from internal surface• Reduce effective wall roughness• Improve hydraulic efficiency (i.e. reduce headloss)

Process: Pre-clean test↓

Clean internal surfaces by high pressure water

blasting↓

Post-clean test



What was measured:

• Pressure at US and DS locations (pressure transducers)

• Flow rate (ultrasonic flowmeters)

• Water level (ultrasonic depth sensors)

• Water temperature

• Machine characteristics


Power Scheme Details

Wilmot Penstock

Tungatinah Penstock 4

Poatina Penstock

Tarraleah Hilltop Pipeline

Output (MW) 35 125 300 90

Operating head (m) 252 300 835 299

Pipeline length (m) 526 877 1684 2141

Penstock diameter (m) 1.98 1.7 - 2.3 2.6 – 3.1 2.6

Improvement in Headloss (m)

1.0 0.8 - 2.0



• Biofilms increase headloss

• Gains in energy production can be made by removing biofouling

• Data plotted on a Moody diagram is not typical of engineering roughness

• Moody diagram extensively used in industry to predict friction losses

• More data over wider range of Reynolds numbers is needed

• New pipe rig at UTAS will be used to gather this data

• Rig in field to grow biofilms

• Rig in lab for detailed testing




Physics of the Flow over Biofilms

Do flows over biofilms conform to same structure as for typical engineering surfaces?

• Grew biofilms on 1m x 0.6m test plates in hydropower canal

• Drag measurements and boundary layer profiles in water tunnel

• Characterised roughness using photogrammetry


Physics of the Flow over Biofilms• Biofilms increase skin

friction drag (measured up to 99% increases)

• No change to mean velocity structure

• Changes to turbulence structure only very close to the wall

• Biofilms thicker on plates with rough surface

• Drag coefficient roughly linear function of max peak-to-valley height of biofilm

0.0 0.5 1.0 1.50.0

4.0

8.0

12.0

(y+e)/d

(U-u

)/u*

Flow over Artificial Biofilms• Skin friction increased by 23%

• No change to mean velocity structure

• Turbulence intensity increased by 50% in region y > 1 mm out to freestream

• Streamers change turbulence structure

• Working on capturing motion using high-speed cameras

• Find frequency of oscillation

Streamers: black Smooth: red

U = 1.0, 1.25, 1.75, 2.0 m/s

0.0 0.5 1.0 1.50.0

4.0

8.0

12.0

(y+e)/d

(%

)U

u2 '


Mitigation & Control• Dewater & physically remove fouling with brooms

attached to tractors

• High pressure water blast in pipelines

• Chemical and heat treatment methods ineffective – majority of biofilm is dead cells and inorganic material

• Long term mitigation

• Provide as smooth a surface as possible

• Increased wall shear – difficult for biofilms to establish

• Trials of different surface coatings – some perform better than others


Summary & Conclusions• Significant improvements to efficiency &

generating capacity can be made by removing biofilms

• Control of biofouling is a global problem, and not just in hydropower

• Current research – understanding wall flows with complex organic interacting surfaces, rather than typical engineering roughnesses

• Climate change policy will see greater investment in renewable energy technologies


AcknowledgementsThis research was funded by:

• 3 Australian Research Council Linkage Grants

• Hydro Tasmania

• University of Tasmania New Appointees Research Grant

The authors also gratefully acknowledge:

A. Barton, K. Perkins, G. Walker, A. Henderson, J. Osborn, A. Leith, G. Hallegraeff, P. Brandner, workshop staff at UTAS, and the many staff at Hydro Tasmania involved in the project.


ICWES15 - Optimising Hydropower Generation through Fluid Dynamics Research. Presented by Dr Jessica...

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