An experimental study of a collector and diffuser system on a small demonstration wind turbine

Abstract

A diffuser-augmented wind turbine (DAWT) has been an attractive concept of wind energy extraction since the early 1970s, due to the system's ability to increase the power generated by a regular bare turbine of the same size. However, the DAWT needs to reach a minimum augmentation ratio of 4 in order to become economically feasible. This paper investigates the possible improvement of a DAWT system by adding a collector fuselage to increase its augmentation ratio. Testing using a small experimental unit shows that adding a collector increases the power augmentation of the DAWT by more than 50%, and increases the mass flow rate through the turbine by increasing the effective upstream area of the wind that enters it. Changing the angle of the incident wind on a collector- and diffuser-augmented wind turbine (CDAWT) shows that it is possible to capture the energy in the wind up to an angle of 71°. Moreover, the CDAWT can keep extracting wind energy, without any diminution of the augmentation ratio, as wind direction varies ±45° from the turbine axes, thus eliminating the requirement for a yaw mechanism. Hence, the variant wind direction has a positive effect on the augmentation ratio.