Orchestrating rectified flows via dynamic morphological variation

A potential explanation for observed flows actively generated by ciliated microorganisms lies in inertial rectification, through a mechanism known as viscous streaming. While conventional streaming theory is well understood for static shapes, it fails to capture effects arising from dynamic morphological variations characteristic of biological settings. Motivated by this, we theoretically investigate these phenomena via the classical 2D squirmer model in Stokes-like regimes, and confirm our findings against direct numerical simulations. Our study elucidates a previously unreported shape-mode effect responsible for flow rectification, providing a potential rationale for the robust and controllable flows exhibited by a variety of aquatic microorganisms.