BASIC-STATE ANALYSIS OF NANOFLUID BIOCONVECTION WITH GYROTACTIC MICROORGANISMS UNDER ZERO-NANOPARTICLE FLUX BOUNDARY CONDITION

Abstract

This study presents an analysis of the basic state of nanofluid bioconvection in a horizontal finite-depth layer containing gyrotactic microorganisms. To enhance the physical realism of the system, zero-nanoparticle flux boundary conditions are incorporated for the nanoparticle fraction. The basic-state solution refers to a simplified, time-independent configuration that serves as the reference or background state for analysing perturbations in stability analysis. In this case, the quiescent flow has zero velocity, while other state variables - such as temperature, nanoparticle concentration, and microorganism density - vary only in the vertical direction. The resulting system of ordinary differential equations is solved to obtain analytical solutions while the effects of key parameters on the steady-state profiles are investigated. The results show that the swimming strength parameter mainly influences microorganism accumulation near the upper boundary. Both the swimming strength parameter and the bioconvection Rayleigh number have only a limited effect on the pressure profile. In contrast, the thermal Rayleigh number and modified diffusivity ratio produce the most noticeable pressure variations, indicating that thermal and thermophoretic effects play the dominant role in shaping the basic-state pressure distribution. Overall, the pressure profile remains nearly linear. The findings provide insight into the role of zero-nanoparticle flux boundary conditions in finite-depth nanofluid bioconvection systems.