Rotation and Oblique Irradiation Effects on Phototactic Algal Suspension Instability

TL;DR

This paper investigates how rotation and oblique light angles influence the stability and behavior of phototactic microorganisms in suspension, revealing rotation's stabilizing and oblique irradiation's destabilizing effects on bioconvection.

Contribution

It introduces a stability analysis of phototactic algal suspensions considering oblique irradiation and rotation, highlighting their combined effects on bioconvective instability.

Findings

Rotation stabilizes the suspension against bioconvective instability.

Oblique irradiation destabilizes the suspension, promoting instability.

The study predicts both stationary and oscillatory instability modes.

Abstract

In this study, we aim to explore the behavior of microorganisms in response to natural lighting conditions, considering the off-normal angles at which the sun strikes the Earth's surface. To achieve this, we investigate the effect of oblique irradiation on a rotating medium, as this combination represents a more realistic scenario in the natural environment. Our primary focus is on understanding the phototactic behavior of microorganisms, which refers to their movement towards or away from light. Under conditions of low light, microorganisms tend to exhibit positive phototaxis, moving towards the light source, while in intense light, they display negative phototaxis, moving away from the light source. By studying a suspension that is illuminated by oblique collimated flux with a constant radiation intensity applied to the top surface, we can gain insights into how microorganisms respond to varying light conditions and rotation. The stability analysis is conducted using linear perturbation theory, which allows us to predict both the stationary and oscillatory characteristics of the bio-convective instability at the onset of bioconvection. Through this analysis, we observe that rotation plays a significant stabilizing role in the system, while oblique irradiation has a destabilizing effect on the suspension.