Abstract
Numerical simulations were carried out modeling the bioconvection generated by chemotactic bacteria in a shallow chamber, and the influence of the Rayleigh number on bioconvection was examined. To confirm the present numerical accuracy, the numerical result was compared with a previous analytical solution. The concentration distributions for a stationary flow field were in good agreement with the analytical solution. Next, the variation of flow and concentration fields with the Rayleigh number was examined. At small Rayleigh numbers, the bioconvection does not occur, and the bacterial cells collect near the free surface. The concentration distributions agree well with the analytical solution for the stationary fluid. At a critical Rayleigh number, bioconvection is formed in the center of the chamber. Since bioconvection increases with an increase in the Rayleigh number, a large difference between concentration distributions above the critical Rayleigh numbers and the analytical solution appears. The bacteria are active near the bottom wall in the chamber because adequate oxygen is supplied from the free surface. When bioconvection occurs, convective transport becomes dominant rather than the transport due to oxygen diffusion and bacterial swimming.
