The evolution of large-scale structures in the wake of oscillating teardrop foils*

The wake of a two-dimensional teardrop foil in combined heaving-pitching motion is examined using Direct Numerical Simulations at a Reynolds number of 6000. The Strouhal number of 0.6, and the amplitude and phase differences between pitching and heaving motions were selected to match the experiments by Van Buren et al. (2018) on the performance of underwater propulsors. These conditions represent the cases of maximum thrust and maximum efficiency. Preliminary analysis suggests that a wider expansion of the wake, which is dominated by the early detachment of structures from the foil, results in higher thrust. However, a higher efficiency locomotion was marked by a smaller wake width that resulted from the elongated detachment of stretched structures. More detailed wake analysis will identify potential differences in coherent structures that result in higher thrust versus higher efficiency.