Environmental pollution and depletion of fossil energy have made the research for the exploitation and use of natural energy more and more intensive in the world, and wind power resources find wide application day by day because it is free of depletion and environmentally friendly.
Precedence has been given to the research on developing high-efficiency wind turbines, and as a result, various types of wind turbines have been developed to provide maximum wind energy.
As well known in the general momentum theory, the performance of wind turbines is characterized by the power coefficient, which is defined as the ratio of mechanical energy to kinetic energy of wind passing through the rotating blade face per unit time.
However, the total kinetic energy of wind mentioned above is not generated by the real wind flowing into the blade inlet because the nearer it gets to the face of blade, the lower the upstream velocity gets due to the pressure caused by the blade of wind turbine.
Kim Mun Hui, a researcher at the Faculty of Electrical Engineering, has presented the theoretical consideration results from the new concept on the rotor swept area.
She applied optimization theory of multivariate functions to describe the power characteristics of wind turbines by the relationship between the upstream area and the rotor swept area. She predicted that the upstream area is 1/1.125 times the rotor swept area and the value of the maximum power coefficient increases to 0.667.
In addition, she confirmed that the maximum value of the power coefficient is kept as 0.667 even in the case of rotors installed in several rows on one axis, and that the total power is not distributed to the rotors in each row, but depends on the rotor in the last row.