The design of costeffective pico-propeller turbines for developing countries Dr Robert Simpson, Dr Arthur Williams
Nottingham Trent University, UK
Project overview
Aim: “to provide an accurate design and design method for the cost-effective manufacture of pico-propeller turbines (<5kW) in developing countries that is scaleable for a range of hydrological conditions” Project partner: Practical Action Peru (formerly known as Intermediate Technology Development Group) Funded by the Leverhulme Trust (UK trust organisation)
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Low head hydro sites (2 to 10m) have great potential for providing electricity in rural areas of developing countries BUT progress appears to be hampered by the lack of a cost-effective reliable turbine design that is appropriate for local manufacture in developing countries Much is known about the design of large Kaplan and propeller turbines but there is little published regarding the design of very small propeller turbines
Objectives
Understand fully the design scale effects for pico-propeller turbines using CFD modeling, laboratory experiments and field 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 that can be used by local manufacturers and engineers Disseminate the information and results of the project which will be made freely available
Stage One
Specify a prototype turbine design based on current knowledge Turbine manufacture, installation and field testing (conducted with Practical Action Peru) Analysis of the turbine performance and investigation of possible improvements using Computational Fluid Dynamics Make modifications to the turbine and compare the field test data to CFD simulations
The turbine site (Magdalena, Peru)
Civil Works: silt basin, concrete channel, pipe and forebay tank
Powerhouse: Tailrace water is returned to irrigation channel
The prototype turbine (general layout)
Turbine layout
Horizontal shaft single stage V-belt pulley driving a 5.6kW Induction Generator as Motor (IMAG) with Induction Generator Controller (IGC) Spiral casing with six fixed guide vanes 90º elbow draft tube
Site specifications
Head = 4m Flow rate = 180-220 l/s
The prototype turbine (Rotor design)
Original rotor design
Diameter: 290mm Blades fabricated from flat plate steel (6mm thick) Blade profile created by bending and twisting the plate to produce camber and twist no nose cone Non-contact seal, with water allowed to leak during operation
Initial operation of turbine
Reported problems:
Redesign options:
During initial operation water emptied from the forebay tank The turbine was not producing sufficient power to get the generator up to operating voltage 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 and determine how the turbine could be modified and put into full operation
Spiral casing simulations
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Total head loss for spiral casing and guide vanes estimated to be 0.43m at 180 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.
Full turbine simulations
CFD Results (original rotor) Power (600 rpm)
Efficiency (600 rpm)
6
60
5
50
4
40
3
30
2
20
1
10
0 200
0 210
220
230
240
250
Flow rate (l/s)
260
270
280
290
Efficiency (%)
Head (m) & Power (kW)
Head (600 rpm)
Comparison of blade geometry
Radius (m) Blade angle (degrees)
0.145 38
0.116 46
Original rotor
0.087 57
0.058 72
Radius (m) Blade angle (degrees)
0.145 17
0.116 21
0.087 27.5
Redesigned rotor
0.058 37.5
CFD Results for rotors (power and flow rate)
Redesigned rotor
Manufactured locally in Lima, Peru by bending and twisting flat sheet metal into 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
Field testing in Peru (experimental technique)
Torque: friction brake Speed: handheld optical tachometer Flow rate: measured from a flume constructed downstream of the turbine Head: height markings measured using water level
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
Blade to Blade view (at mid-span)
Pressure contours in blade to blade view
Possible area of cavitation
Comparison to field tests: (power and flow rate)
CFD Results:
turbine component losses Percentage of Gross Head (4 metres) (speed=800rpm)
Rotor 5% Power output 75%
Losses 25% Spiral casing and guide vanes 11%
Draft Tube 4%
Tailrace 4% Penstock 1%
Scheme costs
Electromechanical Civil Works Electrical Wiring Installation Total Output Power Total Cost per kW Turbine Cost per kW
Cost US$ 3610 10500 500 1000 15610 4 kW 3902.5 $/kW 902.5 $/kW
Conclusions and Future Work Conclusions CFD analysis has been used to identify operational problems with the prototype turbine and has proved to be a useful tool for analysing new rotor geometries. The CFD simulations give a reasonable predicted performance for power output until the maximum power point, however, the flow rate is under predicted resulting in an over estimation of the turbine efficiency by 10%. Future Work Further investigation into producing a profiled rotor with better cavitation performance as 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)
Video
Transient CFD Animation