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.

The lattice Boltzmann method (LBM) is employed to simulate flow around two staggered cylinders within a confined channel. The numerical model is validated against existing experimental data by comparing drag coefficients and Strouhal numbers in the single-cylinder configuration. The study systematically investigates the influence of vertical ( $h$) and horizontal ( $l$) spacing between the cylinders, as well as the Reynolds number ( $Re$ = 0.1–160), on the hydrodynamic forces, streamline patterns, and vortex dynamics. Results indicate that reducing the horizontal spacing $l$ suppresses flow separation behind the upstream cylinder, while either excessively small or large vertical spacing $h$ diminishes separation in the downstream cylinder. The onset of periodic vortex shedding is delayed due to inter-cylinder interactions, with the critical Reynolds number increasing to $R{e}_c$ = 71–112, significantly higher than that of a single-cylinder case ( $R{e}_c$ ≈ 69). During the vortex shedding regime, the downstream cylinder exhibits a greater lift force fluctuation compared to the upstream cylinder. At $Re$ = 160, the root-mean-square lift coefficient ( $C_L^{\prime }$) ranges from approximately 0.17 to 0.56 for the downstream cylinder, and from 0.018 to 0.4 for the upstream one. The shedding frequency, characterized by the Strouhal number ( $St$), increases with Reynolds number, reaching $St$ = 0.12–0.18 at $Re$ = 160. Variations in $h$ and $l$ significantly influence $St$, with a decrease in $l$ or an increase in $h$ lowering the shedding frequency—this effect is more pronounced in the horizontal direction.