Design and analysis on small scale fixed-pitch Straight Bladed Vertical Axis Wind Turbine (SB-VAWTs)

• Main Author: Ji, Xiao Na
• Other Authors: Jorg Uwe Schluter
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Science
• Online Access: http://hdl.handle.net/10356/51144
• Institution: Nanyang Technological University

For the past few decades, researchers working on straight bladed vertical axis wind turbine (SB-VAWT) have faces many challenges in its analysis, modeling and design. This result in the development of the SB-VAWT being very slow which gave rise to the misconception that the SB-VAWTs is inherently inefficient. In this regards, overall performance study on SB-VAWT is necessary. The scope of present research work consists of three main areas, namely: experimental, computational and analytical studies. In the area of experimental studies, wind tunnel tests were carried out a small-scale SB-VAWT fitted with three and four blades. For each case, three different airfoil profiles were tested. This area of work led to the development of a systematic methodology for VAWT testing. The results obtained were used for validation of computational results. In the area of computational studies, a commercial Computational Fluid Dynamics (CFD) software, ANSYS Fluent, was used to perform simulation of the SB-VAWT. In order to demonstrate the technical capability of current software to enable an accurate and fast simulation. Both 2D and 3D validation study were carried out to validate the accuracy and reliability of the software. Good agreements were shown in both cases. The detailed flow visualization of the vortex structure allowed the identification of complex blade interactions. Blockage effects studies were performed to examine the wind tunnel wall effects in the experiment. Significant wall contribution on overall performance coefficient was observed from simulation results. In the area of theoretical studies, a Finite Phase Step Analysis method for predicting the performance of a VAWT was developed. The method employs the single streamtube, two actuator surface model. Starting with the lift curve of airfoil employed for each phase position (azimuth) of the VAWT blade, the torques are averaged over one complete revolution to obtain the power output and hence, coefficient of performance of the turbine. The induced wind velocity interacting with the blade is derived by equating the reaction forces on the blade and the consequent retardation of the wind momentum as it flows through the turbine. Two new concepts, both unseen in prior literature, were employed: 1) for the upwind actuator surface, the retardation of the wind extends beyond the frontal area of the turbine, and, 2) the induced velocity is also the exit wind velocity. Comparison between theoretical and CFD simulation results shown good agreement at upstream, but less correlation at downstream.