Unsteady wake-surface interactions of rapid near-surface swimming

Many natural swimmers, such as dolphins and sailfish, can swim rapidly near the free surface. The underlying unsteady wake-surface interactions are thought to be governed by the unsteady number. However, the unsteady number can arise from either high flow speed with low motion frequency (low Strouhal number, e.g., hydrokinetic energy harvesters) or low flow speed with high motion frequency (high Strouhal number, e.g., accelerating dolphins), leading to distinct unsteady wake patterns. The impact of these different wake patterns, particularly the high Strouhal number related to biological swimming, remains underexplored. To identify the interplay between unsteady and Strouhal numbers, we conducted extensive parameter sweeps covering high unsteady and Strouhal number regimes, closing gaps to rapid swimming in nature. Additionally, 3D Particle Image Velocimetry (PIV) will be conducted to identify key wake features that influence changes in thrust and stability, providing deeper insights into rapid near-surface swimming.