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FACULTY OF ENGINEERING

Design of a small hydro Kaplan turbine with a self-sealing rotor S. Annerel, J. Vierendeels, E. Dick Ghent University Belgium

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Overview • • • • •

Motivation and initial design Sealing rotor Rotor flow analysis Diffuser flow analysis Off-design performance

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Motivation • Turbine that can cope with flow rate variation from design flow rate to zero flow rate • Needs movable rotor that allows complete sealing • Like variable opening valve with extraction of power • Complete flexibility in flow rate • 6 locations on river Sambre in Belgium Flow rate: 5.5 m3/s to 20 m3/s Head: 4.40 m to 1.70 m

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Initial design

Head (m)

3.60

Flow Rate (m³/s)

16.0

Outer diameter (m)

2.00

Inner diameter (m)

0.80

Rotational speed (rpm)

130

Number of blades

12

Lenght diffuser (m)

4.00

Outlet diameter diffuser (m)

2.75

Shaft power (kW)

395

Total efficiency (-)

0.70

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Initial design • Multiple stream tube analysis ‣ Simple radial equilibrium inlet and outlet ‣ No work exchange between streamtubes ‣ Expressed for nine blade sections

• Resulting design:

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Overview • • • • •

Initial design Sealing rotor Rotor flow analysis Diffuser flow analysis Off-design performance

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Obtaining rotor sealingness • Initial design ‣ Rated flow:

‣ Closed:

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Means to reach sealingness • • • •

Stacking (lean and sweep) is not efficient Solidity distribution: large chord at hub Thickness distribution: large thickness at hub Camber distribution: zero camber at hub, large camber at tip • Untwist rotor: large incidence at hub (10.8˚) and negative incidence at tip (-2˚)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Obtaining rotor sealingness • Closed at tip and hub

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Obtaining rotor sealingness • Adjustment of stagger angles: max 1.7˚

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Blade form

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Final design

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Overview • • • • •

Initial design Obtaining rotor sealingness Rotor flow analysis Diffuser flow analysis Off-design performance

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Rotor flow analysis: CFD package FLUENT Flow domain

Inlet Plane Interior Plane (Inlet→Blade) Periodic Plane Interior Plane (Blade→Outlet)

Inlet 600mm

Outlet Plane

Blade

Outlet1 300mm 300mm

600mm

Outlet2

550mm 287mm

1050mm

1050mm 400mm

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Blade surface grid

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Rotor flow analysis • CFD Analysis (SRF, k-ω SST, EWT)

‣ Radius 475mm ‣ Big incidence, but lower than expected ‣ No separation ↑ Relative Velocity Magnitude Vector (m/s) ← Static Pressure Contour (Pa)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Rotor flow analysis

‣ Radius 700mm

↑ Relative Velocity Magnitude Vector (m/s) ← Static Pressure Contour (Pa)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Rotor flow analysis ‣ Radius 925m ‣ Almost zero incidence (small negative incidence)

↑ Relative Velocity Magnitude Vector (m/s) ← Static Pressure Contour (Pa)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Rotor flow analysis Suction side

Static Pressure Contour (Pa)

Relative Velocity Magnitude Vector (m/s)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Flow distribution stream tube analysis

Stream tube

hub

Radius ( m)

0.4

0.475

0.55

0.625

0.7

0.775

0.85

0.925

1

u ( m/s)

5.445

6.466

7.487

8.508

9.529

10.551

11.572

12.593

13.614

c1a ( m/s)

6.813

6.583

6.394

6.233

6.094

5.971

5.862

5.764

5.675

w1u ( m/s)

2.046

3.182

4.297

5.399

6.489

7.571

8.647

9.717

10.782

c2a ( m/s)

6.021

6.074

6.094

6.095

6.087

6.072

6.054

6.033

6.011

w2u ( m/s)

6.619

7.15

7.80

8,.514

9.282

10.094

10.938

11.801

12.676

tip

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Flow distribution CFD analysis

CFD

hub

tip

Radius ( m)

0.4

0.475

0.55

0.625

0.7

0.775

0.85

0.925

1

c1a ( m/s)

4.981

6.011

5.944

5.961

6.022

6.098

6.165

6.200

5.106

w1u ( m/s)

2.305

3.249

4.384

5.472

6.563

7.626

8.692

9.737

10.586

c2a ( m/s)

5.360

6.430

6.238

6.087

5.920

5.880

6.128

5.994

4.930

w2u ( m/s)

7.002

7.645

8.395

9.250

10.104

11.035

11.842

12.697

12.931

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Rotor flow analysis

CFD

hub

tip

radius ( m)

0.4

0.475

0.55

0.625

0.7

0.775

0.85

0.925

1

ΔW ( m²/s²)

25.577

28.423

30.028

32.144

33.743

35.966

36.456

37.267

31.924

Work extracted by turbine is bigger than intended Flow is aligned to tip section: more flow rate, more work Unloading of the hub (fortunate)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Performance • Diffuser recovery factor 0.70 • Stream tube analysis: Q= 16 m3/s, H= 3.60 m Pshaft= 387 kW, ηglob = 0.69 • CFD-analysis Pshaft= 540 kW, Q= 16 m3/s, H= 4.40 m ,ηglob = 0.74 (with mechanical losses: ηglob = 0.72) → rematching necessary

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Rematching

• Work extracted by turbine is too big → allow bigger flow rate • Open stator and open rotor α = 26.5˚ → 23˚ , βtip= 63.5 ˚ → 60˚ Some loss of efficiency ηglob ≈ 0.70

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Overview • • • • •

Initial design Obtaining rotor sealingness Rotor flow analysis Diffuser flow analysis Off-design performance

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Diffuser design • Geometry

Velocity Inlet

Mixing Plane Inlet Blade Cone

Pressure Outlet

Diffuser 370mm

600mm

4000mm

400mm

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Diffuser analysis • CFD Analysis (Mixing plane, k-ω SST) ‣ Static Pressure Contour(Pa)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Diffuser design • CFD Analysis (Mixing plane, k-ω SST) ‣ Radial Velocity Magnitude Contour (m/s)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Diffuser design • CFD Analysis (Mixing plane, k-ω SST) ‣ Axial Velocity Magnitude Contour (m/s)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Diffuser performance verification Analysis planes Inlet rotor →

←Outlet rotor ←Inlet diffuser

Outlet diffuser →

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Diffuser performance: pressure recovery factor

Diffuser maps: LR

L R2

AR

A4 A2

L

4

1 1 2 2 2 Dtip Dhub 2 0.82 2 2 2 2 R4 1.37 2.235 2 R2 0.91652

Cp

0,700

4.364

Cp 0.700

CFD analysis: Cp

p4 p2 1 2 v 2 2

p2 11468.77Pa p4 1608.21Pa v2 6.112 m s

Cp 0.700

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Diffuser performance: α = 26.5˚ → 20˚: post-swirl Velocity variation

Inlet diffuser

Outlet diffuser

Axial Velocity (m/s) → Tangential Velocity (m/s) ↓

Inlet diffuser

Outlet diffuser Inlet diffuser = mixing plane

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent

Outlet diffuser


Overview • • • • •

Initial design Obtaining rotor sealingness Rotor flow analysis Diffuser flow analysis Off-design performance

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Off-design performance: α = 26.5˚ → 20˚ ; β = 63.5˚ → 78˚; Q=8 m3/s (H=3.20 m) • Rotor ‣ Velocity Vector Fields: No separated flow!

↑ Relative Velocity Magnitude Vector (m/s) at radius 475mm

← Relative Velocity Magnitude Vector (m/s) at radius 925mm

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Off-design performance: ηglob = 0.60 • Diffuser ‣ Static Pressure Contour (Pa)

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


Conclusion • Design of an axial hydro turbine with a movable rotor and blade shape such that the rotor can be completely closed was successful • Rated conditions: Q= 16 m3/s, H= 3.60 m Pshaft= 390 kW, ηglob = 0.70 • Half flow rate: ηglob = 0.60

Department of Flow, Heat and Combustion Mechanics – www.FloHeaCom.UGent.be Ghent University – UGent


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