An experimental and computational investigation of a diffuser augmented wind turbine: With an application of vortex generators on the diffuser trailing edge

The Diffuser Augmented Wind Turbine (DAWT) has been studied periodically over the last five decades. It has already been established by the scientific community that the DAWT is superior to conventional bare wind turbines. In spite of this, the DAWT has not gained popularity worldwide due to high manufacturing cost of the diffuser. There are two possibilities to make a DAWT more lucrative; lowering the manufacturing cost or increasing the performance. The present thesis is concerned with the second approach and considers the hypothesis that the generating power of a DAWT can be increased by turbulent mixing of the wake and free stream flow. This mechanism should decrease the diffuser’s exit pressure and consequently increase the mass flow and power. In the present investigation this turbulent mixing is established by placing vortex generators on the diffuser trailing edge. The hypothesis was tested through a series of full scale wind tunnel experiments. The experiments were conducted in the open jet facility of Delft University of Technology in collaboration with Donqi Urban Windmills. It was found that the application of vortex generators on the diffuser trailing edge lead to an increase in power of 9%. Furthermore, in the pursuit of a better understanding of the flow behavior, an inviscid singularity model was formulated. The model uses a surface vorticity technique to simulate the behavior of the diffuser, supplemented with a lifting line approach to model the rotor. It was found that the inviscid model did capture the behavior of the DAWT reasonably well, although when compared to the measurement results it was observed tobe overly optimistic.AEWE - WindenergyAerospace Engineerin