  A new theoretical method is presented for future multi-scale aerodynamic
optimisation of very large wind farms. The new method combines a recent
two-scale coupled momentum analysis of ideal wind turbine arrays with the
classical blade-element-momentum (BEM) theory for turbine rotor design, making
it possible to explore some potentially important relationships between the
design of rotors and their performance in a very large wind farm. The details
of the original two-scale momentum model are described first, followed by the
new coupling procedure with the classical BEM theory and some example
solutions. The example solutions, obtained using a simplified but still
realistic NREL S809 airfoil performance curve, illustrate how the
aerodynamically optimal rotor design may change depending on the farm density.
It is also shown that the peak power of the rotors designed optimally for a
given farm (i.e. 'tuned' rotors) could be noticeably higher than that of the
rotors designed for a different farm (i.e. 'untuned' rotors) even if the blade
pitch angle is allowed to be adjusted optimally during the operation. The
results presented are for ideal very large wind farms and a possible future
extension of the present work for real large wind farms is also discussed
briefly.
