Soon-Duck Kwon has 20 years experiences on windtunnel tests and bridge aerodynamics after completing hisPhD from Seoul National University in Korea.He is currently director of the KOCED Wind Tunnel Center in Chonbuk National University, Korea.
The effect of blockage ratio on wind tunnel testing of small vertical-axis wind turbines has been quantitatively investigated in this study. Darrieus type three blades vertical axis wind turbine was used in the wind tunnel tests. Height and rotor diameter of the turbine were 0.4m and 0.35m respectively. We measured the wind speeds and power coefficients at three different wind tunnels where blockage ratio were 3.5%, 13.4% and 24.7% respectively. The test results show that the measured powers have been strongly influenced by the blockage ratio and the rotor tip speed ratio. The power coefficients generally increase as the blockage ratio and tip speed ratio increases. The power coefficient at blockage ratio of 24.7% reveals two times greater than that at 3.5%. After examining various blockage correction methods, the most of the correction methods are found to be unsuitable for Darrieus wind turbines. The correction methods which use wind velocity drop ratio underestimate the blockage effect, yet the conventional Maskell’s correction method overestimate the blockage effect. Maskell method is basically applicable to the rectangular solid body but the Darius rotor is not a solid body but a porous one. Therefore the present study proposed the modified correction coefficients for the Darrieus wind turbine based on the measurements. The results show that the correction error for power coefficients can be less than 5% when the present correction coefficients apply.
Fatemeh Amiri is doing her Ph.D at Bauhaus university of Weimar, Germany. She has completed her Master of Applied Mathematics at the age of 25 years from Isfahan University of Technology. She has published two papers in fracture mechanics field with Prof. Timon Rabczuk and Prof. Marino Arroyo.
The prediction of fracture in thin structures is of major importance in engineering applications such as aircraft fuselages, pressure vessels, automobile components, and castings. Since analytical solutions provide limited information, there has been a keen interest in numerically simulating fracture in thin shells in recent years. However, despite the advances made in modeling fracture for solid bodies fracture in thin bodies remains a challenge due to the complex interplay between cracks and the shell kinematics and geometry. We present a phase-field model for fracture in Kirchoff-Love thin shells using the local maximum- entropy (LME) meshfree method. Since the crack is a natural outcome of the analysis it does not require an explicit representation and tracking, which is advantage over techniques as the extended finite element method that requires tracking of the crack paths. The geometric description of the shell is based on statistical learning techniques that allow dealing with general point set surfaces avoiding a global parameterization, which can be applied to tackle surfaces of complex geometry and topology. This topic is of high relevance for real-world applications, for example in the automotive industry and in aerospace engineering.