Energy is the main driving force behind the socio-economic development of any society. Traditionally fossil fuels have been used for ages as the primary source of energy. However, with the continuous depletion of natural resources over the last century, civilization has witnessed a significant challenge in identifying new and renewable energy sources. Among various options available for this purpose, wind energy has become a viable alternative, which has experienced exponential growth in the recent past. Large horizontal axis wind turbines have become the signature of any modern and developed society. It converts the energy of inflowing wind into electricity, whose rotor size is proportional to the amount of energy it can extract. Hence, modern horizontal axis turbines have oversized rotors. These flexible blades experience more aerodynamic loads, which ultimately cause significant deformation/vibration with detrimental effects. Blade maintenance is the primary cause of downtime of any operational turbine. Besides blades, tall and flexible towers are equally important as they support generators and drive-train within the nacelle and hence, their design also offers several challenges. Due to these reasons, the analysis and design of modern multi-megawatt wind turbines are complex tasks involving multi-disciplinary challenges. With these in view, the main aim of this research group is to address the following issues
- Develop high fidelity models of combined blade-drivetrain-tower system in the multibody framework. These are carried out either in Kane’s approach or in the finite element framework, as both have certain advantages. Besides modelling the combined system, the aerodynamics of the blade plays a critical role in turbine design. Blades are made of airfoil of different shapes and sizes. The materials and geometry of these airfoils often develop elastodynamic coupling. Thus, the blade dynamics with bending-torsion coupling have drawn researchers' attention as it can have adverse effects. However, efficient modelling indicates that the coupled behaviour can be utilized for load alleviation and flutter enhancement.
- Vibration control of large turbines has remained a significant concern in the industry. Both tower and blade experience significant vibration due to inflowing wind. As the tower provides a stable platform for the turbine-rotor system, its vibration level should be as minimum as possible. The activities of this group on this topic is mainly focused on semi-active and passive vibration controller design. For this purpose, TMD and TLCD have been used whose optimal tuning strategies in the deterministic and stochastic framework are developed. Although passive controllers are relatively easier to tune, semi-active controllers are more robust. However, they have inherent difficulties in tuning as the system matrices are time-dependent. Thus LQR/LQG controllers are developed in a rotating framework using Coleman transformation followed by averaging over the rotational time period. Besides improved controller modelling, input uncertainty also affects its performance. Hence, a reliability-based optimal tuning is also developed that offers the necessary robustness of the controller.
- Modern rotors are oversized for more energy extraction. These flexible rotors experience more aerodynamic force as they grow in size. Hence, efficient rotor design is the need of the hour. The history of existing turbines has shown blade-tower impact during extreme weather conditions. This issue is usually addressed by pre-coning and tilting the drive-train. Although these modifications (i.e. tilt and pre-cone angle) develop more space between the blade and tower, they also produce adverse effects on the gear tooth and blade roots. Thus, an efficient longitudinal stiffening strategy is proposed that improves the blade stiffness without affecting its aerodynamics. SMA based stiffeners are used that can operate in passive or semi-active mode. It not only reduces blade deformation but also improves its fatigue reliability. Besides blade stiffening, current activities are mainly focused on smart rotor design, e.g. double-pitched system. It offers excellent vibration control besides actuator load alleviation.
