MAPUA INSTITUTE OF TECHNOLOGY AT LAGUNA
Academic Year 2018 – 2019
Optimal Darrieus Vertical Axis Wind Turbine for Emergency cases
Aldrin Joshua B. MAGCALS
Carlos S. OLIVEROS
Lance Ian M. RODRIGUEZ
Thesis Adviser: Engr. Allan Alla
A Thesis Proposal Submitted
In Partial Fulfillment of the Requirements for the Degree of
Bachelor of Science in Mechanical Engineering
Review of Related Literature
Introduction of Wind Turbine
Wind turbine has two types, a horizontal-axis and vertical-axis. Horizontal-axis wind turbine (HAWT) is a common commodity for converting wind energy to electricity. It’s reliable when it comes to power output, but it has a disadvantage such as shadow flickering, bird-killing and noise polluting. However, vertical-axis wind turbine (VAWT) is opposite to the horizontal-axis wind turbine in terms of advantages and disadvantages. Vertical-Axis wind turbine (VAWT) is omnidirectional, it can rotate wherever wind direction. And also, it can adapt low wind speed. But the power generated in vertical axis wind turbine is small or low enough to power a small household. Further study required to make the Vertical-axis wind turbine (VAWT) optimal to the community.
Optimal Vertical Axis Wind Turbine
Bedon, Castelli and Benini (2013) found that evolutionary algorithms are thereby utilized to provide optimal configurations for different design objectives. The pure performance and the annual energy production are here considered in order to show the capabilities of the numerical code. A relevant increase in performance is achieved for all the obtained results, showing that the numerical optimization can be successfully adopted in vertical-axis wind turbine (VAWT) design procedures. Many Design are conducted in vertical-axis wind turbine (VAWT) such Darrieus and Savonius type. CITATION Bed13 l 13321 (Bedon, Castelli, & Benini, 2013) The optimization process was conducted in two stages: firstly, a design of experiments-based response surface fitting was used to explore the parametric design space followed by the use of a Nelder–Mead simplex gradient-based optimization procedure. The outcome of the optimization study is a new blade design that is currently being tested in full-scale concept trials by a partnering wind energy company. CITATION Kea16 l 13321 (Kear, Evans, Ellis, & Rolland, 2016). Some researchers analyze the blade by Computation Fluid Dynamics (CFD).
The results obtained from the CFD model were then applied for the construction of an aerodynamic model of an H-type VAWT rotor, which constituted a prerequisite for designing an intelligent pitch angle controller using a multilayer perceptron artificial neural network (MLP-ANN) method. The performance of the MLP-ANN blade pitch controller was compared to that of a conventional controller (PID). The findings demonstrate that for an H-type VAWT, compared to a conventional PID controller, an MLP-ANN results in superior power output. CITATION Abd17 l 13321 (Abdhalraman, Melek, & Lien, 2017).
Liu and Xiao (2015) show that the bending and twist deflection peak is positively correlated with the turbine tip speed ratio ?. For a flexible blade, an unevenly distributed structural stress along the blade with a high stress regime in the vicinity of strut location has also been observed. Due to the rotational motion of a VAWT, the centrifugal force acting on VAWT blade plays an important role on the blade structure characteristics. Reduction of the blade stiffness results in an increase of the blade stress. Changing the strut location from middle to tip will cause a large area under high stress. The results also indicate that the VAWT with a highly flexible blade is not an efficient energy extraction device when it is compared to a less flexible or a rigid blade CITATION Liu15 l 13321 (Liu & Xiao, 2015). and also, Wang Z., Wang Y. and Zhuang (2018) found that the optimal combination is found to appear in the case with an amplitude of 2.5%cb (cb is the blade chord length) and a wavelength of cb/6 for leading-edge serration as well as a blade twist angle of 60°. The simulation results show that the flow separations and torque fluctuations are significantly suppressed due to the passive flow control strategies implemented in the optimized VAWT model. The power output of the optimized wind turbine is found to increase by 18.3% in comparison to the baseline model. In addition, the force fluctuations are observed to be significantly reduced by employing the helical design, which is beneficial for improving the lifespan of turbines. The results derived from this study indicate a better VAWT design for the rural and built environments with relatively insufficient wind energy. Furthermore, Wind turbine can be subjected to the typhoon or high-speed wind that can destroy the system CITATION Wan18 l 13321 (Wang, Wang, & Zhuang, 2018).
Materials of Wind Turbine
We consider some materials in the blade or shaft that can affect the speed and the power output generated in wind turbine. Butbul, Macphee and Beyene (2015) suggested the morphing blade has better performance at low RPMs, but the rigid blade performed better at high RPMs. It was observed that the flexible blade self-started in the majority of the experiments. At high RPM, the centrifugal force overwhelmed the lift force, bending the flexible blade out of phase in an undesired direction increasing drag and therefore reducing the coefficient of performance CITATION But15 l 13321 (Butbul, Macphee, & Beyene, 2015). Thomas and Ramachandra (2018) also proposed Carbon nanotubes are allotropes of carbon with a nanostructure that can have an aspect ratio greater than 1,000,000. These cylindrical carbon molecules have special properties that make them potentially useful in wind turbine blades. Carbon Nano tubes can be reinforced with different types of resins to exhibit different properties CITATION Tho18 l 13321 (Thomas & Ramachandra, 2018).
The mass of the optimized blade is 228 kg, which is 17.4% lower than the initial design, indicating the blade mass can be significantly reduced by using the present optimization model. It is demonstrated that the structural optimization model presented in this paper is capable of effectively and accurately determining the optimal structural layups of composite blades CITATION Wan16 l 13321 (Wang, Kolios, Nishino, Delafin, & Bird, 2016).
Aerodynamic of airfoil
There are two factors can be considering in the aerodynamic airfoil are the Tip speed ratio, the ratio between the wind speed and blade tip speed. The current results indicated to some new shapes suitable for H-rotor Darrieus turbine with considerable performance improvement. It was demonstrated that the symmetric S1046-type is the best performing airfoil for typical tip-speed ratio ranging from 2 to 7 CITATION Has18 l 13321 (Hashem & Mohamed, 2018).
According to Castelli, Del Monte, Quaresimin, et al. (2013) Flow field characteristics are investigated for a constant unperturbed free-stream wind velocity of 9 m/s, determining the torque coefficient generated from the three blades as a function of rotor azimuthal coordinate. The emphasis is subsequently placed on obtaining an estimate for both pressure/tangential forces and centrifugal ones to blade structural loadings, thus assessing the influence of aerodynamic and inertial contributions to blade stresses and deformations CITATION Cas13 l 13321 (Castelli, Del Monte, Quaresimin, & Benini, 2013).
Secondly the Power Coefficient which is proportional to the tip-speed ratio, the maximum percentage increase in power coefficient that the low solidity turbine with three deformable blades can achieve is about 14.56%. When solidity is high and also turbine operates at low tip speed ratio of less than the optimum value, the maximum power coefficient increase for the turbines with two and four deformable blades are 7.51% and 8.07%, respectively. However, beyond the optimal tip speed ratio, the power improvement of the turbine using the deformable blades seems not significant and even slightly worse than the conventional turbines CITATION Yin15 l 13321 (Wang, et al., 2015). Hand, Kelly and Cashman (2017) proposed a solution to exploit offshore wind energy resources in deep water sites. At this large-scale, the VAWT’s blades will operate at high Reynolds numbers and encounter dynamic stall at low tip-speed ratios. In particular, the selection of an accurate turbulence modeling approach is still a challenging undertaking in the prediction of transient blade forces during this complex unsteady event. increasing the Reynolds number showed to be beneficial to the airfoil’s aerodynamic performance as a higher maximum tangential coefficient is attained, owing to the delay in flow separation to much higher angles of attack the Multi-megawatt floating vertical axis wind turbines (VAWTs) CITATION Han17 l 13321 (Hand, Kelly, & Cashman, 2017).
Low wind speed
It is found that the types/patterns, numbers of blades, and height-to-radius ratios have significant effects on mechanical performances whereas types of materials result in shifts of operating speeds of VAWTs CITATION Sra17 l 13321 (Sranpat, Unsakal, Cholijaru, & Leephakreeda, 2017). But Vertical-Axis Wind Turbine (VAWT) is omnidirectional so it will be subjected to low wind speed and placed it in urban community. Again, furthermore research has done and proposed. In unfavorable wind conditions, factors such as low wind speed, high turbulence, and constant wind direction change can reduce the power production of a horizontal axis wind turbine. To overcome the problems above, a novel cross axis wind turbine has been conceptualized to maximize wind energy generation. This is achieved via harnessing the wind energy from both the horizontal and vertical components of the oncoming wind. The cross-axis wind turbine comprises three vertical blades and six horizontal blades arranged in a cross-axis orientation CITATION Cho17 l 13321 (Chong, et al., 2017). According to Wang, Chong and Chao (2018) The results were compared to a traditional straight-bladed VAWT. The performance analyses are evaluated in terms of static performance, dynamic performance, and blade force measurement. The results of static and dynamic performances indicate that CAWT has not only better self-starting characteristics but also higher power coefficients over VAWT. The tangential forces measurement on the horizontal blade of CAWT proves its superior power performance compared to VAWT CITATION Wan181 l 13321 (Wang, Chong, & Chao, 2018). Other thing to maximize the efficiency of Vertical-Axis Wind Turbine (VAWT) by using wind booster according to Korprasertsak and Leephakpreeda (2016).
The wind booster is proposed to be implemented with a VAWT in order to not only harvest energy with low availability at low wind speed, but also enhance performance of the VAWT at high wind speed. Particularly, the wind booster comprises a number of guide vanes, which are mounted around a VAWT. The guide vanes direct wind to impact VAWT blades at effective angles while passages between each guide vane are arranged to accelerate wind. The guiding and throttling effects of the wind booster are able to increase angular speed of a VAWT, leading to an increase in mechanical power of the VAWT CITATION Kor16 l 13321 (Korprasertsak & Leephakpreeda, 2016).
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