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8/10/2019 ES3 Simpson

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The design of cost-effective pico-propeller

turbines for developingcountries

Dr Robert Simpson, Dr Arthur Williams

Nottingham Trent University, UK


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Project overview

Aim:to provide an accurate design and designmethod for the cost-effective manufacture ofpico-propeller turbines (


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Objectives

Understand fully the design scale effects for pico-propellerturbines using CFD modeling, laboratory experiments andfield testing

Investigate, make and test design simplifications and

improvements to be implemented in the field and laboratory

Produce a design manual and simple computer program thatcan be used by local manufacturers and engineers

Disseminate the information and results of the project whichwill be made freely available


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Stage One

Specify a prototype turbine design based on currentknowledge

Turbine manufacture, installation and field testing(conducted with Practical Action Peru)

Analysis of the turbine performance and investigationof possible improvements using Computational FluidDynamics

Make modifications to the turbine and compare thefield test data to CFD simulations


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The turbine site(Magdalena, Peru)

Civil Works: silt basin, concrete channel,pipe and forebay tank

Powerhouse: Tailrace water is returnedto irrigation channel


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Turbine layout Horizontal shaft

single stage V-belt pulleydriving a 5.6kW InductionGenerator as Motor

(IMAG) with InductionGenerator Controller (IGC)

Spiral casing with six fixedguide vanes

90 elbow draft tube Site specifications

Head = 4m

Flow rate = 180-220 l/s

The prototype turbine(general layout)


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Original rotor design Diameter: 290mm

Blades fabricated from flatplate steel (6mm thick)

Blade profile created bybending and twisting theplate to produce camberand twist

no nose cone

Non-contact seal, withwater allowed to leak duringoperation

The prototype turbine(Rotor design)


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Initial operation of turbine

Reported problems: During initial operation water emptied from the forebay tank

The turbine was not producing sufficient power to get thegenerator up to operating voltage

Redesign options: Manufacture a new turbine with different diameter including

spiral casing, rotor and draft tube

Manufacture a new rotor (preferred option due to cost)

Decision:

Use ANSYS CFX to analyse the existing turbine performance anddetermine how the turbine could be modified and put into fulloperation


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Spiral casing simulations

Total head loss for spiral casing and guide vanes estimated to be 0.43m at180 l/s flow rate. Or approximately 11% of gross head at 4 metres.

Fluid angle varied between 22 and 30 degrees from the tangential direction.


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Full turbine simulations


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CFD Results(original rotor)

0

1

2

3

4

5

6

200 210 220 230 240 250 260 270 280 290

Flow rate (l/s)

Head(m)&Power(kW)

0

10

20

30

40

50

60

Efficiency(%)

Head (600 rpm) Pow er (600 rpm) Efficiency (600 rpm)


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Comparison of bladegeometry

Radius (m) 0.145 0.116 0.087 0.058

Blade angle (degrees) 17 21 27.5 37.5

Radius (m) 0.145 0.116 0.087 0.058

Blade angle (degrees) 38 46 57 72

Original rotor Redesigned rotor


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CFD Results for rotors(power and flow rate)


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Redesigned rotor

Manufactured locally in Lima, Peru by bending and twisting flat sheet metalinto the required blade angles

Side effect: Slight S-shape in blade shape due to the twisting at the tip

Nose cone included in new design


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Field testing in Peru(experimental technique)

Torque: friction brake

Speed: handheldoptical tachometer

Flow rate: measured

from a flumeconstructeddownstream of theturbine

Head: height markingsmeasured using waterlevel


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Revised CFD Simulations

Improvements made: The S-shape geometry of the blade was modeled

The penstock volume was included

Changes to the geometry of the spiral casing and guide vane

angles were made based on measurements taken onsite A 3 mm tip gap (3.5% of span length) was modeled

Ongoing research into: Roughness effects

Leakage through the hydrodynamic seal Transient simulations

Various turbulence models

Cavitation modeling


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Blade to Blade view(at mid-span)

Pressure contours inblade to blade view

Possible area of cavitation


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Comparison to field tests:(power and flow rate)


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CFD Results:turbine component losses

Percentage of Gross Head (4 metres)

(speed=800rpm)

Power output

75%

Losses

25%Tailrace

4%

Rotor

5%

Spiral casing

and guide vanes

11%

Penstock

1%

Draft Tube

4%


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Scheme costs

CostUS$

Electromechanical 3610

Civil Works 10500

Electrical Wiring 500Installation 1000

Total 15610

Output Power 4 kW

Total Cost per kW 3902.5 $/kW

Turbine Cost per kW 902.5 $/kW


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Conclusions and Future Work

Conclusions

CFD analysis has been used to identify operational problems with the prototype turbineand has proved to be a useful tool for analysing new rotor geometries.

The CFD simulations give a reasonable predicted performance for power output untilthe maximum power point, however, the flow rate is under predicted resulting in anover estimation of the turbine efficiency by 10%.

Future Work

Further investigation into producing a profiled rotor with better cavitation performanceas well as improvements to the CFD models.

Detailed laboratory testing will be used to complement the CFD results and field tests

Miniature perspex turbine (200W) for a detailed investigation with Laser Doppler Anemometry

Spiral casing propeller turbine of similar construction to the Peruvian prototype (1kW)

Axial flow pump as turbine (approx. 1-2 kW)


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Video


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