I have been reading this paper, which addresses the advantages of diffusers in cross flow turbines.
The abstract says (emphasis is mine):
A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs.
I am confused as to the difference between a duct and a diffuser in terms of turbines.
According to Wikipedia, the diffuser sounds similar to a duct.
a wind turbine modified with a cone-shaped wind diffuser that is used to increase the efficiency of converting wind power to electrical power. The increased efficiency is possible due to the increased wind speeds the diffuser can provide.
My question is, what is the difference between the two? Do they have different functions?
I ask because it seems like the author is implying that the two are different.