Building on our previous work on 2-D pitching airfoils, we explored how forces and torques scale for 3-D pitching airfoils. The terms we added to existing theories were inspired by the 3-D elliptical ring shapes of wake vortices. We validated the new terms by comparing our predictions with water channel experiments over a range of […]
Scaling laws for 3D pitching hydrofoils Read More »
Fish and birds experience different forces when they swim/fly near a flat surface (e.g. seabed, solid ground, still lake). We discovered that the vertical forces they feel switch from negative (downward) to positive (upward) at a particular distance from the surface. In other words, there’s a stable equilibrium altitude where they are neither pushed down
Stable equilibria exist for near-surface swimmers and fliers Read More »
Fish flap their tails asymmetrically to maneuver around obstacles. In contrast, classic fish tail models assume symmetric motions in a uniform flow. We tested how well these classic models work for maneuvering tails. In some cases, the models work well: even 2D wakeless models were able to predict the phase of high frequency lateral displacements.
Modeling lateral station-keeping in fish Read More »
The dorsal and anal fins of fish interact with the tail fins to produce higher thrust and efficiency. We focused on thin elongated dorsal fins, like those of jackfish. We discovered that dorsal fins can act like the wing strakes of fighter jets, promoting flow attachment on a main lifting surface (wing/tail) by inducing spanwise
How dorsal fins make fish faster and more efficient Read More »
We developed a model that estimates how thrust and efficiency change as a pitching hydrofoil gets closer to a planar boundary. Our model predicts that the modified forces are caused by an increasing amount of virtual mass and an increasingly distorted wake. We validated the model by comparing with water channel experiments and inviscid flow
How thrust and efficiency change if you swim near the bottom of the pool Read More »
Animals and bio-inspired robots can swim/fly faster near solid surfaces like the seafloor. In the past, researchers had quantified how strong these effects were for two-dimensional airfoils. We studied how these results extend to the three-dimensional fins. We found that lowering the aspect ratio weakens the effect of the surface: thrust enhancements become less noticeable,
How aspect-ratio affects near-ground swimmers Read More »