In order to solve shortcomings of the fixed pitch Vertical Axis Hydro Turbine (VAHT), such as self-starting difficulty, large fluctuation of main axis load and low efficiency at lower tip speed ratio, an internal layer of blades are added in the traditional single-layer straight blade hydro turbine in this paper. The double-layer fixed pitch straight blade VAHT is calculated using two-dimensional numerical simulation applied by commercial software ANSYS-CFX to investigate effects of geometric parameters on efficiency and loads of the turbine, and to analyze rules of dimensionless force coefficient and power coefficient variable with radius ratio of the rotor, phase difference and chord length ratio of the blade. Moreover, performances between a single- layer and a double-layer turbine are compared. Results show that the force fluctuation of double-layer turbine is relatively stable and start-up performance and efficiency at lower speed of double-layer turbine are better than that of single-layer turbine.
Tidal current energy is a kind of inexhaustible ocean renewable resources. Studies have extensively focused on utilization of tidal current energy (Batten W, 2008; Ju Hyun Lee, 2012; Zhang Liang, 2013) due to many advantages, such as high density, stable and predictable as well as little effects on the environment. Hydro turbines are the core component to capture tidal current energy. Tidal hydro turbines are divided into horizontal axis turbine and vertical axis turbine according to the basis of relationship between the main axis and the direction of flow. The horizontal axis turbine (HAHT) is characterized by the main axis parallel to the flow direction and the vertical axis hydro turbine (VAHT) is the main axis is perpendicular to the flow direction. Compared with HAHT, VAHT has several advantages such as simple blade structure, low costs and easy installation, besides, it has no affected by the incoming flow direction,. VAHTs have been extensively researched and applied in recent years for tidal current energy utilization.