Perpustakaan Digital ITB

Innovation in new technology demand, such as Micro Aerial Vehicle evolved recently for acquiring most favorable value of utilization that is denoted by efficiency parameter. Nature always become part of inspiration and for this interest, many researcher have spent much time on studying the behavior of flying animals to comprehend the fundamental, such as a bird in flight. As to seek bird flight efficiency, it is can be defined from endurance efficiency which is ratio of required aerodynamic power to a unit carried weight. This efficiency can give information about how a bird with its flapping wing motion be able to maintain its flight level for longer flight time. The paper presents the computation of endurance efficiency of a flapping bird flight using computational fluid dynamics approach. Hawk bird model becomes a computational case for studying the effect of flapping parameters on endurance efficiency. The flapping parameters includes, flapping way, flapping frequency, maximum angles of dihedral, retraction and twist. For the computational model, the bird only consider as a flat plate shaped wing model with the planform size based on Hawk bird geometry. The computational simulations are conducted to calculate time-dependent aerodynamic forces and pitching moment of the wing based on the solution of Reynold Averaged Navier-Stokes equation. To capture viscous effect at low Reynolds number of 2.0 x 105 on the wing surface, multi grid structured mesh is required. It is also to hinder numerical problem related to over-lapping mesh during the simulation of wing motion. Mimicking the motion of downstroke and upstroke of bird wing, a sinusoidal function is used. The simulations are carried out for the variation of flapping frequencies, retraction angle, maximum dihedral angle, maximum twist angle, and motion mechanism in order to investigate its effect on aerodynamic forces and moment production. The frequency variation is conducted within the upper and lower values of actual frequency 2.87 Hz as reference frequency of Hawk. Furthermore, dihedral variations is from 10 to 40 degrees. Then, the variations of twist or pitching angles is 12, 15, and 20 degrees. The variation of retraction or hand circumduction angle is 10, 20, and 25 degrees. In addition, the flapping ways are carried in three motions including pure flapping, pure flapping- retraction and symmetrical pure flapping- pitching. From the simulation results show higher flapping frequency yields greater peak aerodynamic coefficient, on the other hand, thrust production is not the same for each case. For the Retraction case, the greater dihedral the higher peak coefficient of lift, in contrary for the coefficient of thrust. For pure flapping motion case, the higher endurance efficiency is produced as decreasing dihedral angle. For the symmetrical flapping-pitching motion case, the higher efficiency produced is produced as increasing pitching angle. Then, the comparison among the motions, the pure flapping and retracting motions has lower efficiency than symmetrical flapping-pitching motion. Therefore, the higher endurance efficiency of the flapping-pitching motion can make better for range performance. The analyzed is also by generating velocity and pressure contours, mesh movement as to see the behavior of flapping motion in detail.