Multiobjective numerical design of vertical axis wind turbine components

Wind energy is regarded as a potentially abundant source of clean and renewable energy for the use of which horizontal axis wind turbines are well-established. An alternative concept is represented by vertical axis wind turbines featuring different opportunities and drawbacks. Basically, the assessment of both concepts is based on the associated cost of energy. Whereas horizontal axis wind turbines are predominant on the worldwide market due to their distinctive technological maturity, the development of vertical axis wind turbines has been neglected in the last 20 years. In this study, the technological potential of straight bladed vertical axis wind turbines is explored. First, the flow field around the rotor is analyzed in detail. In this regard, different geometry and operating conditions are investigated by experiments and numerical simulations, respectively. The results allow an exact choice of optimal geometry and operating conditions with respect to increasing the economic efficiency. In contrast to existing concepts, an active variable blade pitch control and a variable speed operation are taken into account. Furthermore, a comparatively exact, fast and robust hybrid performance prediction model of the fluid mechanical properties is developed. This model allows the choice of the optimal geometry and operating conditions by a systematic optimization based on differential evolution. Different optimization procedures are developed which apply the novel performance prediction model. Each procedure optimizes a certain part of the wind turbine where a combination of all optimization procedures to represent the entire turbine is envisaged for future work. The first optimization procedure determines the optimal geometry and operating conditions in terms of a wind turbine without pitch control. Next, the struts are optimized with regard to the conflicting objectives of thin cross-sections causing only few parasite torque and thick cross-sections providing high moments of inertia which are necessary to support the blades for all occurring operating conditions. Moreover, a complete optimization of the blade pitch variation for all operating conditions of turbines featuring active variable blade pitch control is performed. For this purpose, various optimization procedures are developed with respect to maximum aerodynamic efficiency and minimal structural loading. Gusty wind conditions call for an adaption of the rotational speed of the turbine to maintain the aerodynamic efficiency. A quick and energy efficient realization of the adaption process is benefit by light rotor blades. For this reason, the respective lightweight design process of the rotor blades is developed and conducted. By combining the aforementioned multi-criteria procedures the technological utilization factor of straight bladed vertical axis wind turbines is increased such that the costs of energy are reduced accordingly.