Theoretical performance estimation of shrouded twin rotor wind turbines using the actuator disk theory
Abstract Wind energy is anticipated to play a vital role to fulfill the worldwide energy requirements, whereas existing bare wind turbines can convert only a fraction of flow energy into electricity. To bridge the gap between the escalating demand and the generation capability, we propose a shrouded twin rotor turbine design, whose power coefficient exceeds the Betz Joukowsky limit. We analyze the flow through the wind turbine assembly, using the actuator disk theory, and estimate the power output for a pair of rotor loading coefficients. We find the existence of two regimes in which the proposed design performs better than the single rotor configuration: (a) a turbine turbine mode where both rotors work as turbines and (b) a turbine fan mode where one rotor is a turbine while the other is a fan an idea proposed by Betz (A. Betz, Wind Energie und ihre Ausnutzung durch Windmuhlen, Vandenhoeck, 1926) Both modes enable achieving maximum power for multiple combinations of the loading coefficient pair. Moreover, power output depends solely on a single parameter, defined using the area weighted sum of the loading coefficients. We derive the optimum performance criterion and present the effects of the shroud geometry, back pressure, and flow efficiency parameters on the power output and the performance envelope.
Renewable Energy