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Title: The effect of turbulent flow on wind turbine loading and performance
Author: Mahmoodilari, Mahyar
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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Wind turbines are widely used for electricity generation. Typically turbines are deployed in farms located either on-shore or off-shore. In these arrangements the flow onto a turbine may be turbulent due to the disruption caused by turbines located further upwind. At onshore locations, turbines are typically smaller but will often be located downwind of structures or terrain which will cause the incident flow to be turbulent. Although wind turbines have been employed commercially for several decades, design tools are based on assumptions of quasi-steady flow and the effect of turbulence on turbine performance is not fully understood. In this study the effects of turbulent flow on wind turbine loading and performance were investigated by means of some sophisticated experimental methods in conjunction with numerical predictions. With this intention, the atmospheric boundary layer was simulated using conventional methods within the wind tunnel in the University of Manchester. The characteristics of the flow were established using cross hot-wire anemometry. The maximum thickness for the simulated atmospheric boundary layer that was produced by an arrangement of a combination of vortex generators, a barrier wall and a group of cubes was found to be over 0.7m. This combination sustained the turbulence intensity to between 3% and 23% and the turbulence length scale between 150mm and 210mm for the downstream flow. Meanwhile, the grid turbulence generator produced a turbulent flow at a cross section a distance of five mesh sizes downstream, with 16% turbulent intensity and with 35mm turbulent length scale across the entire cross section. These flow fields were experienced by a designed 2-Dfoil (chord = 60mm, span = 400mm, 40000 < Re < 75000) with the profile NACA4705 alongside a reference flow with no upstream element. These flow conditions were employed to quantify the effect of turbulence characteristics on lift and drag coefficients of the aerofoil prior to implementing the test case in a rotating frame. In addition, numerical simulations were conducted in order to corroborate the results obtained in the 2-D experiment. Further to this, the experiments were carried out on a rotating frame to observe how the turbulent characteristics of the flow might alter the performance of the miniature wind turbine. The blade Reynolds number in the rotor experiments is less than 105 and so considerably reduced from the Reynolds of a full-scale wind turbine. However, since the boundary layer is turbulent the effect of onset turbulence is expected to be representative. The turbine performance was then supported by implementing the Blade Element Momentum theory in the MATLAB environment. In conclusion, the results confirmed that the unsteadiness in the upstream flow associated with the high level of turbulent intensity can enhance the power coefficient of the turbine as a result of increasing the ratio of lift over drag coefficients. However, the large turbulent length scale can substantially diminish the power coefficient.
Supervisor: Stansby, Peter ; Kontis, Konstantinos Sponsor: Beyond Petroleum
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available