Temperature-Difference Driven Aggregation of Pulling- and Pushing-Typed Microswimmers in a Channel

This study employs the fluctuating-lattice Boltzmann method to investigate temperature-gradient-driven aggregation of microswimmers, specifically, pulling-type (pullers) and pushing-type (pushers), within a fluid confined by two channel walls. The analysis incorporates the Brownian motion of both swimmer types and introduces key dimensionless parameters, including the swimming Reynolds, Prandtl, and Lewis numbers, to characterize the influences of self-propulsion strength, thermal diffusivity, and Brownian diffusivity on aggregation efficiency and behavior. Our findings reveal that pushers tend to aggregate either along the channel centerline or near the channel walls under conditions of thermal gradients imposed by heated or cooled boundaries. Notably, pushers can be focused on the channel walls even under minimal temperature differences. In contrast, pullers exhibit sensitivity primarily to heated walls, a phenomenon for which a plausible explanation is proposed. Further analysis identifies the swimming Reynolds number as a critical determinant of aggregation efficiency and performance for both pullers and pushers. Additionally, the Prandtl number predominantly governs aggregation efficiency, while the Lewis number chiefly influences aggregation performance.