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Microorganisms inhabit various natural environments and thrive in diverse ecosystems, including freshwater and marine bodies. Many of these microorganisms can swim and have a higher density than water, generating a vertical stratification of cell concentration that may lead to instability due to the buoyancy force. Biothermal convection refers to the convective motion that arises due to the combined effect of up-swimming microorganism and thermal gradients in a fluid medium. In the present work we investigate the onset of biothermal convection in a horizontal layer of cold water in the presence of the density inversion. This previously unexplored issue holds significance due to its potential applications in both natural and industrial contexts. We applied linear stability analysis to determine the critical thresholds at which instability initiates. To confirm these stability findings, we conducted numerical simulations using the finite volume method and compared them with the available experimental results in the case of penetrative convection. The critical threshold is shown to depend essentially upon the value of the density inversion parameter and the thermal Rayleigh number. Additionally, the linear stability analysis suggests the possible occurrence of Hopf bifurcations at the onset of motion.
Article Highlights
Biothermal convection stability depends on both the thermal Rayleigh number and the density inversion parameter.
The temperature stratification can either stabilize or destabilize, depending on the density inversion parameter.
An increase in the thermal Rayleigh number can introduces wave number transitions.