Numerical and theoretical analysis of falling plume and its applications caused by bioconvection of microorganisms

The purpose of this research is to analytically and numerically investigate the formation and applications of bioconvection caused by microorganisms. The falling plumes in bioconvection with a suspension saturated with porous medium are studied theoretically. Utilizing bioconvection to mix and uniform solid particles are studied numerically. Large particle settling in bioconvection is also included in this research.; The formation of falling plumes as observed in suspensions of these bacteria in experiments is explained in this research. A suspension of motile oxytactic bacteria that consume oxygen and swim up the oxygen gradient is considered. A utilized model that is based on a quasi-steady approximation is established. Based on the approximate solution, a similarity solution of full governing equations that describe fluid flow as well as oxygen and cell transport in the plume is obtained.; Settling of small solid particles in a suspension of motile gyrotactic microorganisms is investigated numerically. Bioconvection induced by the upswimming of microorganisms enhances mixing between the particles and leads to a more uniform number density distribution of solid particles across the layer depth. The case that a bioconvection suspension that contains two types of particles is considered. It is found that the number density distribution of solid particles of one type impacts that of particles of the other type as well as that of microorganisms.; Settling of one or two large solid particles in a bioconvection flow induced by gyrotactic motile microorganisms is investigated as well. Chimera method is utilized to generate subgrids around the moving particles. Equations for calculating values on moving boundaries in the streamfunction-vorticity formulation are developed. It is demonstrated that bioconvection can either accelerate or decelerate settling of the particle depending on the initial position of the particle relative to the plume center. Settling of one particle can displace bioconvection plume and change its shape. Introducing the second particle can either further displace the plume or make this displacement smaller depending on the initial releasing positions of the first and second particles.