Yasuaki Ito

Fundamental Study on the Efficiency of Power Generation System by Use of the Flutter Instability

Recently, Isogai et al.[1] proposed a new idea on power generation by use of flutter instability of thin airfoil. The heaving steady oscillation, which produces the electrical power from wind energy, can be excited by the forced torsional oscillation initially given to the heaving and torsional 2DOF system at any wind velocity ranges in his study. On the other hand, the authors have investigated the coupled flutter mechanism of various bluff bodies from the point of two different torsional and heaving branches by use of the “Step-by-Step flutter analysis method” (abbreviated by the SBS method).[2,3,4] Isogai’s idea is identical to the heaving branch flutter in the SBS method. Thus, the improvement of the power generation performance is investigated in this paper basing upon the flutter mechanism, and the efficiency of power generation by use of the heaving branch flutter was compared with that by the torsional branch flutter. It has been clarified that the obtained energy by the heaving oscillation would be larger than the supplied energy for giving initial torsional oscillation to the system and loss-energy caused by the structural damping and the aerodynamic damping over certain wind velocity range.Copyright

SPAN-WISE CORRELATIONS OF FLUCTUATING LIFT FORCES ON 2D RECTANGULAR CYLINDERS

The span-wise correlations of fluctuating lift forces on 2-dimensional rectangular cylinders are evaluated using LES. High base pressure is supposed to result in high correlation of wind forces, but the correlation for rectangular cylinder with B/D=2.0 is higher than that of B/D=1.0 even though the base pressure for B/D=1.0 is much higher than B/D=2.0. This characteristic is caused by the vortex scale. The vortex scale in main flow direction become large according to the value of 1/ St, and the scale in span-wise direction is related to the scale in main flow direction. Then, the correlation is characterized by the vortex intensity and the vortex scale around the body, which are closely related with the base pressure and the Strouhal number respectively.