The onset of bio-thermal convection induced by a combined effect of gyrotactic and oxytactic microorganisms

Purpose - The purpose of this paper is to investigate the stability of a suspension containing both gyrotactic and oxytactic microorganisms for the case when the suspension occupies a horizontal layer of finite depth. The lower boundary of the layer is assumed rigid while at the upper boundary both situations of rigid and stress-free boundary conditions are considered. Design/methodology/approach - Linear instability analysis is utilized, and the obtained eigenvalue problem is solved analytically using a one-term Galerkin method. Findings - The obtained eigenvalue equation relates three Rayleigh numbers, the traditional thermal Rayleigh number and two bioconvection Rayleigh numbers, for gyrotactic and oxytactic microorganisms. Research limitations/implications - Only the case of non-oscillatory instability (which always occurs when heating from the bottom is considered) is analyzed. Further experimental research is needed to elucidate possible interaction between gyrotactic and oxytactic microorganisms. The developed theory is applicable only for dilute suspensions. Originality/value - This paper extends the traditional theory of bio-thermal convection to the case when the suspension contains two types of motile microorganisms exhibiting different behaviors.