Motion of a single microalga with one defective flagellum

We experimentally identify a rotational motion of a single microalga ( Chlamydomonas reinhardtii ) within a microcontainer believed to be induced by one defective flagellum. We numerically adapt the classic two-dimensional squirmer model to replicate this unique motion by partially inhibiting the slip velocity on the boundaries of the squirmer. Subsequently, we employ a lattice Boltzmann method to simulate the motion of the single microalga with one defective flagellum. We examine the influence of swimming Reynolds numbers, self-propelling strength ( $\beta$ ) and angle ( $\alpha$ ) on the locomotion of the squirmer with one defective flagellum. The results indicate that a large $\beta$ leads to a large rotational diameter, positively correlating with the speed. Additionally, we observe that a low self-propelling strength ( $\beta =0.5$ ) yields a monotonically increasing speed for the squirmer with $\alpha$ . In general, high $\beta$ values result in fast speeds for the squirmer. This differs from the behaviour observed in a classic squirmer ( $\alpha =360^{\circ }$ ), where high $\beta$ leads to a slow speed of puller ( $\beta \gt 0$ ) owing to weak fluid inertia effects. Meanwhile, the energy expenditure increases monotonically with $\alpha$ , contrasting with the non-monotonic trends observed for swimming speed and rotational diameter.