| 1. |
- Odemark, Ylva, et al.
(författare)
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The effects of a model forest canopy on the outputs of a wind turbine model
- 2014
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Ingår i: Journal of Physics, Conference Series. - : Institute of Physics Publishing (IOPP). - 1742-6588 .- 1742-6596. ; 555:1
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Tidskriftsartikel (refereegranskat)abstract
- The effects of a rough surface boundary layer on the outputs of a wind turbine model were investigated experimentally in a wind tunnel. The very rough surface consisted of cylindrical pins, in order to model a forest canopy. The hub height of the turbine model was varied in order to see the effect of the presence of the model forest in the power and thrust coefficients. A small effect of the hub height was observed in the averaged power coefficient, where the turbine produced less for the lowest hub height. The difference was however reduced when scaling the power output with the available power in the wind instead of using the velocity at hub height. Consistent trends were present in the standard deviation of the thrust coefficient and the rotational speed, which both increased by decreasing the hub height. This underlines the fact that not only the rotor but also the tower and the bearings of a wind turbine must withstand to increased loads when operating close to a canopy.
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| 2. |
- Odemark, Ylva
(författare)
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Wind-turbine wake flows - Effects of boundary layers and periodic disturbances
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increased fatigue loads and decreased power output of a wind turbine placed in the wake of another turbine is a well-known problem when building new wind-power farms and a subject of intensive research. These problems are caused by the velocity gradients and high turbulence levels present in the wake of a turbine. In order to better estimate the total power output and life time of a wind-power farm, knowledge about the development and stability of wind-turbine wakes is crucial.In the present thesis, the flow field around small-scale model wind turbines has been investigated experimentally in two wind tunnels. The flow velocity was measured with both hot-wire anemometry and particle image velocimetry. To monitor the turbine performance, the rotational frequency, the power output and the total drag force on the turbine were also measured. The power and thrust coefficients for different tip-speed ratios were calculated and compared to the blade element momentum method, with a reasonable agreement. The same method was also used to design and manufacture new turbine blades, which gave an estimate of the distribution of the lift and drag forces along the blades.The influence of the inlet conditions on the turbine and the wake properties was studied by subjecting the turbine to both uniform in flow and different types of boundary layer in flows. In order to study the stability and development of the tip vortices shed from the turbine blades, a new experimental setup for phase-locked measurements was constructed. The setup made it possible to introduce perturbations of different frequencies and amplitudes, located in the rear part of the nacelle. With a newly developed method, it was possible to characterize the vortices and follow their development downstream, using only the streamwise velocity component.Measurements were also performed on porous discs placed in different configurations. The results highlighted the importance of turbine spacings. Both the measurements on the turbine and the discs were also used to compare with large eddy simulations using the actuator disc method. The simulations managed to predict the mean velocity fairly well in both cases, while larger discrepancies were seen in the turbulence intensity.
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