Numerical Analysis of Bioconvection Generated by Chemotactic Bacteria

Abstract

The present study performed numerical simulations of bioconvection generated by chemotactic bacteria in a shallow chamber, and examined influences of Rayleigh number upon the bioconvection. The present results are in good agreement with the previous linear theory in stationary flow field. At the small Rayleigh number, the bioconvection does not occur, and the bacteria cells collect near the free surface. The difference between the numerical result and the linear theory appears with an increase of the Rayleigh number owing to the influence of the non-linearity. At the critical Rayleigh number, the cell near the free surface becomes unstable by the Rayleigh-Talor instability, and the bioconvection is formed in the center of the chamber. The bioconvection grows with further increase of the Rayleigh number. The bacteria are active near the bottom of the chamber because the oxygen is supplied by the diffusion from the free surface. When the Rayleigh number increases, the convective transport becomes dominant by reason of the generation of the bioconvection as compared with the oxygen diffusion and bacteria swimming.