Hydrodynamic interaction between two swimming bacterial flagella in a viscous fluid - a numerical study using an immersed boundary method

We investigate the hydrodynamic interaction and the resulting propulsion between flagella of two bacteria swimming in a viscous fluid based on a three-dimensional computational model developed using an immersed boundary (IB) method. Numerical simulations are performed to demonstrate the swimming of flagella in side-by-side and in tandem arrangements. In side-by-side arrangement, both the flagella swim with nearly the same swimming speed. Also, the swimming speeds of the flagella are higher compared with swimming alone in a viscous fluid under the same physical and initial conditions. It is noticed that in side-by-side arrangement, offsetting one flagellum from the other significantly reduces the propulsion speeds and their orientation from the initial helix axis. The hydrodynamic interaction and the propulsion of the flagella in tandem arrangement are also investigated. It is revealed that in tandem arrangement, the flagellum in the front side swims faster than the flagellum in the back. Also the swimming speeds largely depend upon the separation distance between the flagella which indicates the influence of the hydrodynamic interaction among the flagella. With small separation distance, higher values of swimming speeds are obtained for both the flagella.