Three-dimensional numerical analysis of bioconvection generated by chemotactic bacteria

Abstract

The present study performed three-dimensional numerical simulations of bioconvection generated by chemotactic bacteria in a shallow chamber, and examined influences of Rayleigh number upon the bioconvection. Bacteria concentration becomes unstable with an increase of the Rayleigh number. At the critical Rayleigh number, the bacteria near the free surface create a three-dimensional plume and generate bioconvection. Since the surrounding fluid is entrained to the bottom by the plume, a vortex ring is generated. At the high Rayleigh number, the plume extends toward the bottom. Amount of bacteria near the free surface decreases due to extension of the plume, while amount of bacteria near the bottom increases. Delay time decreases with increasing of the Rayleigh number. This result is qualitatively similar to the previous experimental data. When the Rayleigh number increases, the convective transport becomes dominant due to the generation of the bioconvection as compared with the oxygen diffusion and bacteria swimming.