Inertial Marangoni Propulsion: Simulation

We study the Marangoni-driven motion of a disk-shaped particle located at a flat air-water interface sitting atop a deep layer of water. The particle self-propels thanks to the release of an active agent from its rear that locally reduces the surface tension. The release is set such that the resulting surface tension gradients produce no rotating torque about the direction of propulsion if the motion is straight. Hence, provided that outer boundaries are symmetric and no external perturbations are present, the Marangoni surfer is expected to undergo a pure translation. However, we have found experimentally that, at high enough Reynold numbers, the left-right symmetry is broken spontaneously, which gives rise to the rotation of the particle. After the initial rotation, the particle follows a nearly circular path until it runs out of the "fuel" or gets close to the boundaries. Here, we numerically examine whether a perturbation in the lateral velocity of the particle can lead to its spontaneous and self-sustained circular motion. Such a perturbation may lead to the asymmetric shedding of vortical structures that appear on the sides of the particle at high speeds. The asymmetric vortex shedding could then be responsible for the particle rotation and its subsequent trajectory.