Techniques to Produce Typical Engineering Products - Term Paper Example

MANUFACTURING TECHNOLOGY The Blades of 10KW Horizontal Axis Wind Turbine Submitted to To demonstrate your extended knowledge and understanding of general manufacturing processes and techniques to produce typical engineering artifacts and products. To apply your knowledge and understanding of general manufacturing processes and techniques to analyse and specify manufacturing requirements for specific engineering artefacts and products. To apply computer aided design and manufacturing techniques with reference to particular manufacturing and product requirements. Dr. M.Galis 1. Introduction Wind is a source of non conventional power. Wind power is generated by conversion of the energy contained in wind into electricity through wind turbine. A horizontal wind turbine has its rotor axis aligned horizontally. The blades of a wind turbine act in the fashion of the aircraft wings. The wind flows over the blade resulting in its motion because of combination of lift and drag forces action over it. Generally there are three blades in one turbine. But smaller turbines may have more that three also. Thus the blade has to be designed and manufactured in a way that they are reliable and economical. There are various parameters that are considered for turbine blades. They are blade materials, diameter, power rating, length, wind speed and working temperature to name a few. This assignment endeavours to highlight the manufacturing aspect of the blades for a 10kw horizontal axis wind turbine. The areas that will be covered in this assignment are the material selection, process description, design parameter review and quality control aspects. Figure: Generalised wind turbine system 2. Components of Wind Energy System The basic components are: A rotor with blades: When the wind blows over the blades, the rotor turns, causing the generator to rotate and produce electricity. A gearbox: This is used to synchronise the rotor speed to that of the generator. The turbines of 10 kW and less usually do not require a gearbox. A tail vane: This helps in aligning the turbine with the wind direction. A Tower: To mount the rotor at given height from the ground. Electrical system to generate electricity. Figure: Schematic diagram of horizontal wind turbine(Source: www. Ontario.ca) 3. Design Parameter for wind system 3.1. Wind Availability The economic viability of wind turbine depends most strongly on the quality of wind resource. In order to be cost effective, a 10 KW wind turbine will require on an average minimum wind speed of 4.0-4.5 m/s. Figure: Relationship between wind speed and wind power(Source: www. Ontario.ca) 3.2. Height of Tower Height of the tower is a very important consideration for the power of the wind turbine. As a matter of fact the power derived from the wind is proportional to the cube of its speed. At the same time the wind speed increases as we go higher. So as the height of the tower increases the power and hence the amount of electricity generated by a wind turbine will also increase. Figure: Wind speeds increase with height(Source: www. Ontario.ca) 3.3. Coefficient of performance The power developed by turbine blades by flow of air stream under a steady state is given by following relationship Where the symbols represent ρ = air density (nominally 1.22 kg/m3) R = radius of area swept by the turbine blades υ = speed of moving air stream Cp = “coefficient of performance” for the rotating blades (Composite aerofoil) It must be kept in mind that Cp is not a constant for a particular airfoil, but it is further dependent on a parameter λ, which is known as the tip-speed ratio. Thus λ is defined as the ratio of the speed of the tip of the blade to the speed of the moving air stream. As a matter of fact, the wind speed and air density are factors beyond the control. Moreover the radius of the blades is also fixed as the size is a constraint. This leads to the inference that the performance coefficient is the only parameter which can be used to control the torque. This coefficient of performance is the attribute for the mechanical control. Very often the turbines blades are designed in a manner that Coefficient of performance falls noticeably at high wind speeds. This method of controlling the aerodynamic torque is known as stall regulation. Figure: Coefficient of performance (Cp) for a modern wind turbine blade assembly as a function of tip-speed ratio (λ) and blade pitch (β, in degrees). 3.4. Cost Through the literature survey is estimated that the cost of the energy produced by wind turbines of 10 kW and less is roughly $0.07/kWh. This analysis can be used to carry out the breakeven analysis of the blade manufacturing. Following diagram represents the economic estimate. Figure: Estimated cost for electricity produced by small wind turbines (10 kW) (Source: www. Ontario.ca) 3.5. Turbine Size The empirical relationship indicating the size of the turbine need for given energy output is as follows: AEO = 1.64 D2 V3 Where the terms are: AEO is Annual energy output expressed in kWh/year D is the rotor diameter expressed in meters V is the Annual average wind speed expressed in m/s Figure: Theoretical power production for small wind turbines (10KW) (Source: www. Ontario.ca) Figure: power curve for a small wind turbine rated at 10 kW (Source: www. Ontario.ca) 4. Design Parameters for turbine blade 4.1. Chord Chord is defined as the width of a wind turbine blade at a given location along the length. 4.2. Twist Twist In a blade is defined as the difference of Pitch between the blade root and the blade tip. In general, more pitch is at the blade root for easier Start-up, and less pitch is at the tip for better high-speed performance. 4.3. Tip Speed Ratio The ratio of speed of blade tip and the wind speed is called the tip speed ratio. It shows how much faster than the wind speed the blade tips are moving. 5. Product Description Blade Materials: Fibre glass Rated power: 10 KW Rated voltage: 240V Rotor diameter: 8 m Start-up wind speed: 2m/s Rated wind speed: 10m/s Security wind speed: 45m/s Rated rotating speed: 150rpm Tower height: 12m Working temperature: -40º C 60º C 6. Material and method Choices for Blade The wind turbine blades are made of fibre-reinforced epoxy or unsaturated polyester. The prevailing processing method used with these materials is vacuum infusion of the resins. The main advantages reaped out of using these materials are production of less expensive and lighter blades. Some manufacturers also use woven glass to manufacture the blades. It is composed of 70% to 75% glass by weight. In this case the method used is Prepreg moulding. Woven glass fabric is more costly but offers greater consistency because it already contains the matrix material (typically epoxy). Both epoxy and polyester, has been the conventional choice since early days. Polyester has an advantage of easier processing and cost effectiveness. On the contrast the epoxy has an advantage of better mechanical performance especially in terms of better tensile and flexural strength. Moreover in contrast with epoxy, polyester does not needs any post-curing but the blades are heavier. Another option of the carbon fibre is also used but rarely as it is very costly. But at the same time the carbon fibre has an advantage of stiffness and reduced weight. At a price of $10 to $13/lb, carbon fibre costs 15 to 20 times more than woven glass. Whatever material be used, the blades must meet very stringent mechanical requirements of High rigidity High resistance to torsion High resistance to fatigue These stringent requirements are because the blades are subjected to high static and dynamic loads over a span of wide temperature range. Thus reviewing all the aspects, the material which can be used for this case of 10 KW turbine blades is fibre-reinforced epoxy, as a very high strength is not required. Moreover it will be cost effective along with being light. Accordingly the method which can be used is vacuum infusion. 7. Manufacturing Process Plan As the blades are smaller in size, the process of vacuum infusion can be used that will makes blades in one piece. This will get rid of processing two separate shells and also will get rid of gluing irregularities. This Integral blade manufacturing technology will use epoxy and will be a closed process. The moulding system has two parts. There is a closed outer mould and inside there is a flexible and expanding, bladder. Now under the vacuum at high temperature in the mould, the epoxy resin is injected and the blade is cured. Once the blade is cured, the blade is removed from the outer mould while the inner bladder is collapsed with a vacuum and pulled from the blade. And hence a seamless one-piece blade can be obtained. The advantages, that can be reaped off with method will be: Shorter cycles More efficient use of manpower and space. Only one mould set is required Least tolerance The blade is an integral structure with no glued joints so no potential threat of weakening due to cracking, water entry, and lightning strikes. The process is used to make blades for wide range of dimensions. The mould specification must be as follows: Radius Ratio Chord ratio Twist (Degree) 5 5.2 29.5 15 7.8 19.5 25 8.6 13.0 35 7.6 8.8 45 6.6 6.2 55 5.7 4.4 65 4.9 3.1 75 4.0 1.9 85 3.2 0.8 95 2.4 0.0 Here the blades are supposed to operate at constant speed and at constant pitch angle. Structural properties of the blade section are estimated for three spans of different thickness distributions. These are baseline, thicker and thickest respectively. The thicker and thickest span utilizes the airfoils that have considerably more thickness in order to reduce weight and to improve the structural performance. Following table indicates the blade thickness distribution. Radius Ratio Thickness Ratio (t/c) Baseline Thicker Thickest 5 100 100 100 15 42 52 62 25 28 38 48 35 24 32 40 45 23 27 33 55 22 24 26 65 21 21 21 75 20 20 20 85 19 19 19 95 18 18 18 Figure: Blade section at 15% span Figure: Blade section at 25 % span Figure: Blade section at 45% span 8. Quality It is very important from the view point of efficient functioning of the wind turbine system that the blade must be manufactured within the given tolerance limits. In order to achieve this tolerance limits. Statistical process control can be applied to the manufacturing process. The level of tolerances must be maintained within level of 99%. This means that the specification limits are up to three standard deviations from the mean. Upper Control Limit (UCL) = Mean+ 3 Lower Control Limit (LCL) = Mean+ 3 Figure: Normal distribution of the process and deviation level for the tolerances 9. References 1. Blade Manufacturing Improvements: Development of the ERS-100 Blade: Project: Final Report, TPI Composites, SAND2001-1381, May 2001. 2. Zuteck, M.; “The Development and Manufacture of Wood Composite Wind Turbine Rotors”, Proceedings of the Large Horizontal-Axis Wind Turbines Conference,DOE CONF-810752, SERI/CP-635-1273, July 1981. 3. Stroebel, T., Dechow, C, and Zuteck, M.; Design of Advanced Wood Composite Rotors, Gougeon Brothers, DOE/NASA/0260-1, NASA CR-174713, December 1984. 4. Zuteck, M. and Miller, M.; Hawaii Zuteck Rotor Project: Compilation of Project Reports, NREL/SR-500-26086, November 1998. 5. Abbott, I.H., and von Doenhoff, A.E., Theory of Wing Sections,McGraw Hill. 6. Tangler, J.L., and Somers, D.M., "NREL Airfoil Families for HAWTs,"NREL/TP-442-7109, Jan. 1995. 7. Drela, M., "Newton Solution of Coupled Viscous/Inviscid Multielement AirfoilFlows," AIAA Paper 90-1470, June 1990. 8. Giles, M.B., and Drela, M., "Two-Dimensional Transonic Aerodynamic Design Method," AIAA Journal, Vol. 25, No. 9, Sep. 1987, pp. 1199-1206. 9. Drela, M., and Giles, M., "Viscous-Inviscid Analysis of Transonic and Low Reynolds Number Airfoils," AIAA Journal, Vol. 25, No. 10,Oct. 1987, pp.1347-1355. 10. Internet Resource Information for Renewable Wind Energy Atlantic Wind Test Site Canadian Wind Energy Association Canadian Association for Renewable Energies Canadian Renewable Energy Network Renewable Energy and Sustainable Energy Systems in Canada Energy Centre of Wisconsin (US) Home Power Magazine (US) The National Wind Technology Center Wind Energy Weekly (US) 11. Contact Information Canadian Renewable Energy Corporation Wind Resource Evaluation Systems Campbell Scientific Canada Corp., 11564–149 St.Edmonton, Alberta T5M 1W7 Phone -(705) 454-2505 12. NRGSystems 110 Commerce St, Hinesburg, VT 05461 USA, Phone: (802) 482-2255 Email: sales@nrgsystems.com Read More