1 erik dick - design of a small hydro kaplan turbine with a self sealing rotor

FACULTY OF ENGINEERING

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

Ghent University – UGent

Design of a small hydro Kaplan turbine

with a self-sealing rotor

S. Annerel, J. Vierendeels, E. Dick

Ghent University

Belgium



Overview

• Motivation and initial design

• Sealing rotor

• Rotor flow analysis

• Diffuser flow analysis

• Off-design performance



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



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



Initial design

• Multiple stream tube analysis

‣ Simple radial equilibrium inlet and outlet

‣ No work exchange between streamtubes

‣ Expressed for nine blade sections

• Resulting design:



Overview

• Initial design

• Sealing rotor






Obtaining rotor sealingness

• Initial design

‣ Rated flow:

‣ Closed:



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˚)




• Closed at tip and hub




• Adjustment of stagger angles: max 1.7˚



Blade form



Final design



Overview

• Initial design

• Obtaining rotor sealingness






Rotor flow analysis: CFD package FLUENT

Flow domain

Inlet

Blade

Outlet1

Outlet2

1050mm

550mm

300mm300mm

1050mm287mm

400mm

600mm

600mm

Interior Plane (Inlet→Blade)

Periodic Plane

Interior Plane (Blade→Outlet)

Inlet Plane

Outlet Plane



Blade surface grid



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)



Rotor flow analysis

‣ Radius 700mm





Rotor flow analysis

‣ Radius 925m

‣ Almost zero incidence

(small negative incidence)





Rotor flow analysis

Suction side

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



Flow distribution stream tube analysis

Stream tube hub tip

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



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



Rotor flow analysis

Work extracted by turbine is bigger than intended

Flow is aligned to tip section:

more flow rate, more work

Unloading of the hub (fortunate)

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



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



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



Overview

• Initial design







Diffuser design

• Geometry

4000mm

400mm

600mm

370mm

Mixing Plane

Inlet

Blade

Cone

Diffuser

Velocity Inlet

Pressure Outlet



Diffuser analysis

• CFD Analysis (Mixing plane, k-ω SST)

‣ Static Pressure Contour(Pa)



Diffuser design


‣ Radial Velocity Magnitude Contour (m/s)



Diffuser design


‣ Axial Velocity Magnitude Contour (m/s)



Diffuser performance verification

Analysis planes

←Outlet rotorInlet rotor →Outlet diffuser →

←Inlet diffuser



Diffuser performance: pressure recovery factor

Diffuser maps:

0,700pC

2 2 2 22

44.364

1 12 0.8

2 2tip hub

L LLR

R D D

2 24 4

2 22 2

1.372.235

0.9165

A RAR

A R

4 2

22

1

2

p

p pC

v

2

4

2

11468.77

1608.21

6.112

p Pa

p Pa

v m s

0.700pC

0.700pC

CFD analysis:



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

Inlet diffuser

Outlet diffuser

Inlet diffuser

Outlet diffuser

Outlet diffuserInlet diffuser

= mixing plane

Axial Velocity (m/s) →

Tangential Velocity (m/s) ↓

Velocity variation



Overview

• Initial design







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!


at radius 475mm

← Relative Velocity Magnitude Vector (m/s)

at radius 925mm



• Diffuser

‣ Static Pressure Contour (Pa)

Off-design performance: ηglob = 0.60



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

1 erik dick - design of a small hydro kaplan turbine with a self sealing rotor

Documents