Kathmandu University

Study of Sediment Erosion in Guide Vanes of

Francis turbine

Ravi Koirala1,2, Hari Prasad Neopane1, Baoshan Zhu2, Bhola Thapa1

April, 2017

1Turbine Testing Lab, Department of Mechanical Engineering, Kathmandu University, Dhulikhel, Nepal2State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing, China

CRHT VII, 2017 Kathmandu University 2

Contents

Background

Sediment Erosion in Guide Vanes

Research Focus

Investigation through GV cascade

Investigation through RDA setup

Conclusion

CRHT VII, 2017 Kathmandu University

Background

Global Initiative to utilize renewable technology – hydropower is flexible and

consistent renewable energy source

Production cost consistency, low operation and maintenance cost and

environmental acceptability make it more reliable

Prior to developing new projects, identification of existing problems, its

causes, severity and mitigation approach is essential

3

Figure Global sediment deposition proportion and undeveloped resources [Edenhofer, Madruga, & Sokona, 2011], [Gleick, 1993]

CRHT VII, 2017 Kathmandu University

Background

Sediment - major problem with turbines operating in Nepal – where prime electricity

source is hydropower

Francis turbine is projected to be one of the most used system in future projects

Turbine Testing Lab, Nepal

Working in developing erosion resistant Francis turbine

Earlier attempts on design optimization of runner has set the scope of research

Guide Vanes

Stationary component in Francis turbine performing movement as per

requirement through pivoted support

Regulates flow to runner

4

CRHT VII, 2017 Kathmandu University

Background

• Clearance gaps are applied to allow

movement of vane though pivoted

support

– Cross flow occurs through this gap

• In presence of sediment in water:

– Increases gaps

– Increases roughness

– Affects life and performance

5

Figure Clearance Gap in Francis turbine

Figure Cross Flow though Guide Vanes

CRHT VII, 2017 Kathmandu University

Sediment Erosion in Guide Vanes

• Turbulence Erosion

• Secondary Flow Erosion

• Leakage Flow Erosion

• Acceleration Erosion

6

Figure Summary of Guide Vane Erosion Mechanisms

CRHT VII, 2017 Kathmandu University

Sediment Erosion in Guide Vanes

7

Figure Sediment Erosion in faces of Guide Vanes

Figure Sediment Erosion at Guide Vane edges and facing plate

CRHT VII, 2017 Kathmandu University

Sediment Erosion in Guide Vanes

8

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Cle

ara

nce G

ap w

ith F

acin

g P

late

[m

m]

Guide Vane Position

8500 Hours

16500 Hours

Figure Clearance gap measurement location

Figure Guide Vane Erosion at A+C

Figure Guide Vane Erosion at B+D

0

1

2

3

4

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Cle

ara

nce G

ap w

ith F

acin

g P

late

[m

m]

Guide Vane Position

8500 Hours

16500 Hours

CRHT VII, 2017 Kathmandu University

Observation

• Erosion on Leading edge, trailing edge, faces and clearance gaps

were observed

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CRHT VII, 2017 Kathmandu University

Research Focus

• Prior to development of Francis turbine to address regional problems-

laboratory estimation is essential

• Experimental investigation of erosion is a destructive process

• Simplified system is required

• Forward two possible approaches on laboratory estimation of erosion:• Rotating Disc Apparatus [RDA]

• 3 Guide Vane Cascade System

10

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Investigation though 3GV setup

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Figure Design method of 3 Guide Vane setup

Figure CFD analysis of flow cascade

Meridional Velocity

Tangential Velocity

CRHT VII, 2017 Kathmandu University

Investigation though 3GV setup

12

Figure Position-wise tangential and normal velocity distribution at Guide Vane Outlet

CRHT VII, 2017 Kathmandu University

Investigation though 3GV setup

13

Figure Experimental Setup for erosion testing in 3 Guide Vane system

Pressure Tank

Tank Outlet

Tank Inlet

Bypass

Sand Hooper

Sump Tank

3GV Test Setup

Operating Conditions

Head 0.1 MPa

Flow 0.006 m3/s

Sediment Feed

rate

7.8 gm/sec

Particle size 150 – 300 µm

CRHT VII, 2017 Kathmandu University

Investigation though 3GV setup

0

0.2

0.4

0.6

0.8

3 6 9 12 15 18 21

% C

um

ula

tive

Wei

ght

Lo

ss

Weight of Sediment passed [Kg]

Figure Mass loss with respect to sediment passed

Figure Effect of erosion on pressure around guide vanes

Figure Erosion on Aluminum Guide Vanes

0

2

4

6

8

10

3 9 15 21

% P

ress

ure

Chan

ge

Sediment Passed [kg]

P1

P2

P3

CRHT VII, 2017 Kathmandu University

Investigation though RDA setup

Figure Experimental practice in Rotating Disc Apparatus

Disc speed 458 rpm

Sediment Concentration 66.67 gm/ltr

Particle size 150 – 300 µm

CRHT VII, 2017 Kathmandu University

Investigation though RDA setup

0

0.26

0.52

0.78

1.04

1.3

NACA0012 NACA2412 NACA1412 NACA4412

% W

eig

ht

los

s

Profiles

30 mins 60 mins 90 mins

Figure Selection of Guide Vane Profile for erosion handling

CRHT VII, 2017 Kathmandu University

Conclusion

• Erosion on Leading edge, trailing edge, faces and clearance gaps were

observed

• Simplified setup is essential for testing

• 3GV setup and RDA is suitable option

• Effect of erosion in terms of weight loss and flow around vanes can be

observed

17

Kathmandu University

Thank you for your attention!

Contact :

Turbine Testing Lab

ttl@ku.edu.np

www.ku.edu.np

Kathmandu University,

P.O. Box : 6250

Phone : +977-011-661399

ravikoirala@ku.edu.np