Fig. 2: Rotational behavior of squirmers at \({{{\rm{Re}}}}=0.8\).
a Orientation correlation functions C(t) for pullers (β = 5) and passive colloids at different temperatures. Here, t refers to the simulation time. A no-slip boundary condition is enforced between squirmers and monomers. The decrease in the redness (for the puller, active stress β = 5) or purpleness (for the passive colloid) of the C(t) curves indicates a reduction in temperature. Solid lines show simulation results, while dashed lines represent fitted curves obtained using the fitted rotational diffusion coefficients \({D}_{r}^{a}=1.2,1.8,6.8\times 1{0}^{-6}\,{\tau }^{-1}\) for pullers and \({D}_{r}^{p}=4.7\times 1{0}^{-8},4.3\times 1{0}^{-7},4.8\times 1{0}^{-6}\,{\tau }^{-1}\) for passive colloids at kBT/ε = 0.0005, 0.005, 0.05, respectively. Vertical lines indicate error bars, which become larger in the long-time regime due to limited statistics. Time is normalized by the characteristic time scale τ0 = 3R/B1 = 1800 τ, which corresponds to the time required for a swimmer to traverse one body length. (b) Rotational diffusion enhancements \({D}_{r}^{a}/{D}_{r}^{p}\) for swimmers with the no-slip (ns, dashed line) and repulsive (rp, solid line) boundary conditions. Here, β denotes active stress. Blue, red, and green lines correspond to pushers, pullers, and neutral swimmers, respectively. The rotational diffusion coefficients for passive colloids with the no-slip boundary condition are \({D}_{r}^{p}=4.7\times 1{0}^{-8}\), 4.3 × 10−7, and 4.8 × 10−6 τ−1 at temperatures kBT/ε = 0.0005, 0.005, 0.05, respectively. For the repulsive boundary condition, the values are \({D}_{r}^{p}=4.9\times 1{0}^{-8}\), 4.5 × 10−7, and 4.2 × 10−6 τ−1. The snapshots show representative configurations of squirmers with the no-slip boundary condition at kBT/ε = 0.0005. The dotted line represents the reference curve.
