Abstract
Abstract. The article describes results of experimental wind tunnel testing of four different straight-bladed vertical axis wind turbine model configurations. The experiment tested a novel concept of vertically dividing and azimuthally shifting a turbine rotor into two parts with a specific uneven height division in order to limit cycle amplitudes and average cycle values of bending moments at the bottom of the turbine shaft to increase product lifetime, especially for industrial-scale turbines. Testing reduction effects of simultaneously including a vertical gap between turbine rotor levels, increasing shaft length but also reducing aerodynamic interaction between rotor levels, has also been performed. Experiment results have shown very significant decreases of bending moment cycle amplitudes and average cycle values, for a wide range of measured wind speeds, for dual-level turbine configurations as compared to a single-level turbine configuration. The vertical spacing between levels equal to a blade's single chord length has proven to be sufficient, on laboratory scale, to limit interaction between turbine levels in order to achieve optimal reductions of tested parameters through an operating cycle shift between two position-locked rotor levels during a turbine's expected lifetime. CFD validation of maintaining the effect on industrial scale has been conducted, confirming the initial conclusions.
Highlights
Vertical axis wind turbine (VAWT) blades, unlike horizontal axis wind turbine blades, work in a high range of angles of attack within each rotation cycle (Ahmadi-Balouaki et al, 2014)
The proposed concept for limiting those factors focuses on separating the rotor vertically into two or more parts of different lengths, shifted azimuthally in such a way as to maximally reduce maximum moment values and amplitudes at the bottom of the rotor shaft in a rotation cycle
While factors related to the blade tip not moving faster relative to the rest of the blade, allowing for lower noise emissions (Iida et al, 2004), lower bird death rates and no ice block launching, in areas where the risk exists, as compared to horizontal axis wind turbines (HAWTs) are important advantages for certain siting conditions, the key factor that keeps drawing researchers to VAWTs is the high aerodynamic efficiency potential
Summary
Vertical axis wind turbine (VAWT) blades, unlike horizontal axis wind turbine blades, work in a high range of angles of attack within each rotation cycle (Ahmadi-Balouaki et al, 2014). Spiral-bladed wind turbines are described in the literature as having lowered amplitude changes of their aerodynamics (Guo et al, 2019) – the time amplitude of the sum of force values affecting the entire rotor is much lower for a standard spiral VAWT compared to a straight-bladed VAWT – as presented visually within the Journal of Power and Technology (Scheurich et al, 2011). Another study gives this relationship an averaged numeric value – stating that by replacing straight blades with helical ones in a VAWT rotor, the total force fluctuation amplitude is reduced by about 50 % (Marini et al, 2010). Both structural concerns and increased weight of spiral blades make the technology very interesting on small to medium scales but less cost-efficient than the concept validated within this paper, on the scale referenced and above
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