  Recent analytical models concerning the limiting efficiency of marine
hydrokinetic (MHK) turbines are reviewed with an emphasis on the significance
of blockages (of local as well as global flow passages) and wake mixing. Also
discussed is the efficiency of power generation from fully developed turbulent
open channel flows. These issues are primarily concerned with the
design/optimization of tidal turbine arrays; however, some of them are relevant
to wind turbines as well.
