Fish Swimming Stability

Depatment of Mechanical Engineering, 

University of Michigan

We demonstrate that a (nearly) neutrally buoyant hydrofoil motion is unstable during gliding motion. However, powered undulatory motion becomes directionally stable.  Two-dimensional solutions of the Euler equations show that the unsteady wake plays the important role.  We show that a very simple inviscid model can mimic fast starts, turning maneuvers, and steady swimming.  The case is made for abandoning the usual thrust versus drag context of examining this flow and instead show that swimming speeds and power consumption are more easily interpreted swimming measures. We will update our latest directional stability analyses.