AbstractsEngineering

With the increasing size and complexity of wind turbines, also the risk of failure of a crucial component increases. The expected fatigue life of certain subcomponents is an important design requirement. Fatigue damage is triggered by a periodic loading of the construction. The number of load-cycles (and thus the lifetime) and the amplitude of the periodic loading dominate the fatigue behavior. The lifetime greatly increases if the load amplitude is decreased. One of the possible ways to reduce the periodic behavior of the loading is by applying flaps to the blades of a Horizontal Axis Wind Turbine (HAWT). The flap deflections can be preprogrammed to counteract the periodicity of aerodynamic phenomena like wind shear or yawed operating conditions. In the future, it should even be possible to add a sensing system, calculating in real-time the required flap deflections. With this 'Smart' autonomous system, possibilities open up to even use the control surfaces for non-periodic peak loads occurring due to turbulence or wind gusts. In this master thesis, an aerodynamic model (Vortex Panel Code) is used to investigate the loads on the blades of the HAWT. The simulated wind turbine is an experimental rotor which will be tested in the Open Jet Wind Tunnel Facility (OJF) at the TUDelft. The loads for three different cases are calculated. In a first simulation, the reference condition is analyzed, i.e. the rotor is operating in pure axial inflow. Secondly, the turbine is operating under yaw misalignment. This simulation gives the uncontrolled (and mostly unwanted) periodic behavior of the blade loads. Finally, the effect of a prescribed flap deflection is analyzed. When the output of the flap deflection case is compared to the output of the yaw misalignment case, it is possible to make an estimation of the required flap control in order to reduce or even eliminate the periodic behavior of the loading. The obtained estimations indicate that the smart rotor concept is useful to compensate for periodic structural loadings, but it is not very suitable for applications where the purpose is to level a periodic output of the rotor power.