Numerical Investigation of 3-D Effects on Thrust Generation of Flapping Airfoils

2-D and 3-D flows over flapping airfoils are computed, and thrust generation and propulsive efficiencies are compared. The flapping motion of the airfoils is described by a combined harmonic plunge and pitch motion. The flows are computed for flapping motions which produce maximum thrust and propulsive efficiency, predicted by a gradient based optimization algorithm using a 2-D flow solver. 2-D and 3-D flow computations are both performed in parallel. PVM and MPI message passing libraries are used. 3-D simulations resulted in slightly higher thrust and efficiency values than 2-D predictions. Both 2-D and 3-D numerical simulations show that high thrust may be obtained at the expense of reduced efficiency. For high propulsive efficiency, the large scale formations at the leading edge are prevented.