Salar Heyat Davoudian - Ph.D. Student, Sharif University of Technology
Khodayar Javadi - Assistant Professor, Sharif University of Technology

In nature, microorganisms are swimming in the water at very low Reynolds numbers. When they make the colonies, the Reynolds number has been increased even more than ۱۰. In the following paper, the colonies of the microorganisms are modeled by a micro-cylinder and the flow field and the drag forces around this cylinder have been computed. To obtain more physical results and to determine the viscous and pressure drag forces, thedissipative particle dynamics method (DPD) has been applied. To validate the numerical method and the boundary conditions, two benchmark problems, i.e. liddriven cavity flow and the fully developed channel flow, have been considered. The flow field around the microcylinder is also carried out at four Reynolds numbers (۱۰, ۱۵, ۲۰, and ۲۵) and the results are compared with the experimental and the numerical results. The velocity andvorticity contours and profiles are presented and the DPD results are in close agreement with FEM. In the last part, the total, pressure, and viscous drag forces are obtained in different Reynolds numbers and the relation between intermolecular forces and the drag forces are investigated.Keywords: Microorganisms’ Colonies, DPD, Viscous Drag, Pressure Drag.

Microorganisms’ Colonies, DPD, Viscous Drag, Pressure Drag.