Seyed Ali Mousavi, Mohammad Reza Elhami,
Volume 15, Issue 9 (11-2015)
Abstract
Variable pitch propeller (VPP) are used in advanced helicopters, in order to achieve greater efficiency, better stability and achieve higher altitudes. This study is going to assess the behavior of VPP propeller with coupled non-linear displacement in three degrees of freedom. Accordingly, the behavior of this type of propeller with Changes of elastic axis distance, Length, mass, speed, polar radius of gyration, Stiffness in three degrees of freedom, and pitch have been investigated. In this paper, Gallerkin method is used to extract natural frequencies and the results were evaluated with the results reported by other researchers. The results show convergence and accuracy of the used method. In this study, it was found that parameters of mass, length and rotational speed of the propeller have effect on the natural frequencies, and all modes of vibration. However, other parameters except for the pitch angle effect on the odd or even number of frequency modes. It was also found that the pitch angle in the static mode does not effect on natural frequencies but in the case of rotation of propeller, affect on natural frequency of vibration modes as sine or cosine form.
A. Hosseini Moghadam Omami , Y. Yassi, A.f. Najafi, A. Nourbakhsh ,
Volume 19, Issue 2 (2-2019)
Abstract
Hydro screw is a small micro-hydro turbine. Due to increase in demand for clean energy production, a comprehensive project at the Iranian Research Organization for Science and Technology (IROST) for the design and construction of very small turbines (micro-turbines), including hydro screw, has been developed. Hydro screw is suitable for a low head and discharge that does not have a guide vane and draft tube; thus, it is simple, small, inexpensive, and portable. This turbine, with a 15 cm blade diameter, can generate power up to 2 kW. Hydro screw blade is inspired by the Archimedes turbine, and difference between them is that the blade pitch of hydro screw is variable and horizontally mounted. In this project, the effect of spiral variable pitch on turbine has been studied numerically. Based on the results, it was found that the turbine had the best efficiency at a spiral pitch of 1.5. Subsequently, the small model of hydro screw was made and tested in the laboratory. The results of this study have been presented in the form of standard curves of turbine performance and the accuracy of the results has been proved by comparison of numerical and experimental results. The results show the integrity of the numerical calculations and, therefore, they can be used in line with next turbine studies. The results indicate that the maximum turbine output is between 62% and 68%.
