Pusat Pengajian Kejuruteraan Aeroangkasa - Tesis

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Hydrokinetic savonius turbine for sustainable energy in low-speed flows
(2024-01-01)
Abdullah, Mohd Safie
Hydrokinetic turbine (HKT) technology is both cost-effective and reliable, producing clean energy with minimal environmental impact. The goal of this research is to improve the power performance (𝐶𝑝) of a Savonius HKT in a low-speed river in Malaysia (Re < 1.5 × 105). Two methods are proposed to improve 𝐶𝑝 in this study. The first method involves developing and optimizing a novel blade profile using 3D CFD simulation with a systematic Design of Experiment (DOE). The best design out of 625 options was determined statistically using the Taguchi method and analysis of variance (ANOVA). The novel blade enhances 𝐶𝑝 by approximately 10.9% compared to the conventional design at optimal tip-speed ratio (TSR) (best 𝐶𝑝 = 0.159) and 16.7% improvement at higher TSR value of 0.9 (𝐶𝑝 = 0.158). Moreover, the novel blade outperforms the nature-inspired blade (golden spiral blade profile) by 27% in terms of efficiency. The second method focuses on developing and optimizing a new augmentation device called the wake accelerator. The device utilizes the Magnus Effect to improve overall flow by altering the wake profile behind the turbine. The Taguchi method and ANOVA were used to optimize the size, position, and location of the device. The 𝐶𝑝 improved by 83.73% at TSR = 1.1 (best 𝐶𝑝 = 0.4450). Additionally, this thesis investigates the effect of turbine size on structural behavior during stationary operation under various loading conditions. It provides insights into stress concentration around the turbine rotor, potential issues, and the optimal rotor angle for maintenance to minimize the stress. The computational fluid dynamics (CFD) and finite element analysis (FEA) simulations in this study are well-established and validated for precision and accuracy .
An investigation into the influence of material properties on the performance of savonius turbines in hydrokinetic applications
(2023-09-01)
Mohamed Shamsuddin, Muhamad Syukri
Savonius hydrokinetic turbines (HKT) are practical for off-grid power generation due to their simplicity, self-starting capability, and low-speed requirement. Although the impact of turbine material selection on durability has been established, there is still limited research on its influence on the turbine’s power performance. Therefore, this research aims to investigate the effect of different material properties on the performance of a conventional, two-bladed Savonius rotor. The turbine’s performance was evaluated in three key aspects: power performance, self-starting characteristics, and flow structure. Based on the gap found in the literature review, three different material properties were investigated: weight, surface roughness, and stiffness. The study also considered the effect of water absorption as the turbine is developed for hydrokinetic applications. The experiment was conducted at various Reynolds numbers, R3 ranging from 5.22 ×104 to 9.40 ×104. The turbine performance was then compared in wind and water testing using the principle of dynamic flow similarity. Findings from the power performance analysis were then used to rank five different materials using multi-purpose decision-making analysis (MCDM). Results from the wind tunnel testing suggested that the 𝐶pmax increased with increasing R3, with the highest increment (150%) recorded at 5.22 ×104 to 6.27 ×104. The 𝐶pmax was also found to increase with increasing weight, increasing surface roughness, and decreasing stiffness. The highest 𝐶pmax increment was recorded at 220%, 201%, and 30%, respectively. However, the influence of material properties was significantly influenced by the variation in R3, indicating that some materials may be advantageous within specific ranges of flow speed. For water absorption, the 𝐶𝐶𝑃𝑃 performance of all turbines was found to be less affected, despite having deteriorated flexural strength property of up to 62.3%. The MCDM analysis revealed that soft plastic like poly-lactic acid (PLA) would have a higher performance index at R3 ≤ 6.27 ×104. However, at higher R3, i.e., R3 ≥ 7.31 ×104, conventional materials like aluminium (ALU) turbines would outperform the other materials. The outcomes of the current study demonstrated the impact of various material properties on the power performance of the Savonius turbine, emphasizing the significance of the material selection process particularly for power enhancement.
Numerical and experimental study of passive control in the form of ribs at sonic and supersonic mach numbers
(2023-10-01)
Khan, Ambareen
Flow from Converging and Converging-Diverging nozzles expanded suddenly into the enlarged duct has been investigated experimentally and numerically, with emphasis on the base pressure, and the development of flow in the duct. In this investigation, the variables considered are the Mach number, Nozzle Pressure Ratio, area ratios, rib geometry, and rib size. Experiments were conducted to control the flow by a semi-circular rib at sonic and supersonic Mach numbers. Results show nozzles flowing under favorable pressure become effective and there is a significant increase in the base pressure. Numerical simulations were done for three area ratios (i.e. 3.61, 5.76, and 7.84) using three shapes of the ribs (i.e. Rectangular, triangular, and semicircular) of three different sizes (i.e. 6 mm, 8 mm, and 10 mm diameter) for four rib locations (i.e. 1D, 2D, 3D, and 4D) at sonic and supersonic Mach numbers. As experimental tests were conducted up to NPR 10 nozzles remained over-expanded for Mach 2.2 and 2.5. To account for design NPR and beyond the numerical simulations were done up to NPR = 25. As a first step CFD results were validated with the experimental results for semi-circular ribs. Among the three shapes of the ribs rectangular ribs seem to be the best option and result in a maximum increase in the base pressure. While scanning the wall pressure in the duct, the flow field is not aggravated due to the presence of various ribs, and the flow field with and without control remains the same.
Elucidation of the rotor aerodynamics and performance of a self-starting darrieus turbine
(2023-03-01)
Selvarajoo, Shaza Rae
Global warming and over consumption of non-renewable energy sources are amongst the grand challenges facing humanity in the 21st century, where wind turbines provide an alternative source of power. However, wind flows in nature fluctuate greatly, which causes Darrieus turbines, a subset of vertical-axis turbines, to be in protracted transient modes that reduce their overall efficiency. The complex flow patterns surrounding these rotors, due to their interactions with multiple shed vortices, further exacerbate the reduced efficiency and complicate the elucidation of the rotor aerodynamics. In this work, a three-bladed H-Darrieus rotor was simulated numerically via a combination of the lifting line theory and vortex wake model, with their algorithms embedded in a software named QBlade. These algorithms model the entire self-starting process that consists of the linear and acceleration phases. Darrieus rotors face difficulty self-starting because of dead bands in the linear phase, where each dead band is a region when a net negative torque is generated over a single cycle due to a reverse dynamic stall. In the accelerated phase, significant torque is generated due to forward dynamic stalls, which then cause the rotor to enter the steady phase. The work herein elucidates the aerodynamics of a Darrieus rotor during self-start, via the use of a novel and newly developed in-house software named DRAFA. This software allows users to rapidly analyse Darrieus turbines, which significantly reduces the time taken to process raw data into insightful data. Its most significant aspect is the production of turbine vector diagrams which allow users to intuitively visualize the complex and spatio-temporally evolving inflow and force vectors on the turbine blades.
Parametric study on the effect of venting performance of savonius turbines for hydrokinetic applications
(2023-09-01)
Abu Bakar, Nurul Asyikin
Renewable energy has become increasingly significant in Malaysia particularly with the utilization of hydrokinetic energy to generate electricity from rivers and streams. However, despite the advantages of its simple design and compact size, the efficiency of the Savonius turbine is limited by negative torque. To address this issue, researchers have explored improvements such as incorporating vented blades that minimize the negative torque produced by returning blades. These efforts have predominantly focused previously on the elliptical Savonius blade rather than the conventional blade. Therefore, the investigation into optimized vent configurations for conventional blades remains scarce. This study aims to parametrically investigate the effects of various vent configuration parameters particularly on position, width and height, on the performance and flow structure of a Savonius turbine operating at a Reynolds number of 148 000. The finding reveals that variations in vent height have greater impact on turbine performance compared to vent position and width. The H3 turbine exhibits the highest performance of CP = 0.1520 with a 16.95% improvement over the conventional Savonius turbine achieved by utilizing an optimal vent configuration of 45 ° position, a width of 0.011 m, and a height of 0.071 m, resulting in a substantial increase in net torque. The top view flow visualization reveals a closer recovery flow behind the advancing blade in the H3 turbine, contributing to the enhanced net torque. The side view flow structure demonstrates a smaller wake size downstream, indicating the effectiveness of the H3 vent configuration in reducing excessive turbulence on the returning blade, thereby increasing the power coefficient. In conclusion, this study provides a comprehensive insight into the influence of different vent configurations on the performance and flow structure of Savonius turbines. The findings help to establish and contributes valuable knowledge for future applications in sustainable power generation systems, highlighting the importance of optimizing vent parameters to enhance turbine efficiency and overall performance.

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