Diffuser Augmented Wind Turbine (DAWT) technologies: A review

Diffuser Augmented Wind Turbines (DAWT) are an optimised class of wind turbines that use a Diffuser to accelerate and direct air flow onto a wind turbine rotor to drive it for higher rpm and power output than without the Diffuser. This power output is typically rated in terms of the power augmentation. Diffuser design and theory was pioneered in the 1970's with a recent re-emergence in a range of new technological approaches that are designed for laminar wind profiles, low exit pressures, improved pressure recovery, improved torque generation and adaptability to wind directional and speed changes. Computational Fluid Dynamics (CFD) theory and software has been crucial in the advancement of design and performance of DAWT's. Power augmentations have been achieved within the range of 2-3 for small-medium scale turbines, though this is largely in theory than in practice. In this review, ground-based Diffuser technologies have been presented according to rotor type, i.e. horizontal- and vertical-axis. Large-scale on-shore and off-shore concepts have been presented along with airborne technologies. Building-integrated DAWT's are then presented with a description of some of the influential economic and technical factors that currently affect the development of the DAWT industry. The current DAWT industry is mostly research-based with very little commercialisation as the majority of technologies presented here are in their early developmental stages. Innovations in issues associated with the increased weight of a Diffuser, the effects of loading, turbine stability, vibrational effects during operation and yaw angle effects are necessary in the advancement of DAWT's.