Figure 4. Prediction of relative equilibria in the wake of a solitary swimmer.

(A, B) Snapshots of vorticity and fluid velocity fields created by a solitary swimmer in computational fluid dynamics (CFD) and vortex sheet (VS) simulations and corresponding flow agreement parameter $𝕍$ fields for a virtual follower at $\varphi =0$. Locations of maximum $𝕍$ values (i.e. peaks in the flow agreement parameter field) coincide with the emergent equilibria in inphase pairwise formations (indicated by black circles). Contour lines represent flow agreement parameter at ±0.25, ±0.5. Thrust parameter $𝕋$ is shown at $\ell =0$ and $\ell =0.5L$. A negative slope $\partial 𝕋/\partial d$ indicates stability of the predicted equilibria. See also Figure 1—figure supplements 1 and 2.