Ranjith Maniyeri

Numerical Study on the Dynamics of Organism Motion under Background Flow

We propose a two-dimensional numerical model to investigate the dynamic behaviour of an organism swimming in a background flow in a channel. In this work, the organism is modeled as a neutrally buoyant one-dimensional elastic filament based on an immersed boundary finite volume method. Further, the organism is modeled using discrete number of immersed boundary points and the Navier-Stokes equations governing the flow are solved on a staggered Cartesian grid system. A driving function is applied which results in a wave travelling along the length of the organism from left to right. It is found that under no background flow, the organism swim in the forward direction (right to left) when the wave travel over the organism is in the opposite direction. It is observed that, under a uniform background flow, a non-motile organism is simply dragged by the flow whereas a motile organism swims backward along the direction of flow. Further, it is seen that a propulsion enhancement is found in the case of organism swimming along the flow direction when the wave travel is in the opposite direction as that of the flow.

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.

Numerical Study on the Interaction of an Inextensible Filament in a Uniform Fluid Flow Using the Immersed Boundary Method

Numerical modeling of fluid-structure interaction problems are challenging in the field of computational fluid dynamics because of the complex geometries involved and freely moving boundaries. Flapping of an inextensible filament in a uniform fluid flow is such a problem which mimics the swimming of energy harvesting eel fish. Recently, immersed boundary method has found much attention in simulating fluid-structure interaction problems due to its easiness in grid generation and memory and CPU savings. In the present work, we employed an improved version of immersed boundary method proposed by Shin et al. [1] which combines the feedback forcing scheme of the virtual boundary method with Peskin’s regularized delta function approach. A FORTRAN code is developed for the simulation of flexible filament flapping in a uniform fluid flow. The code is validated for the bench mark problem of two-dimensional flow over a circular cylinder. A single filament hanging under gravitational force is simulated using the developed code which is analogous to a rope pendulum and the results are compared with available analytical results. The results are found to be in good agreement. Finally, the interaction of the flapping filament in the uniform fluid flow is studied for different flow and structure parameters. The production of a series of vortex procession obtained in the case of flapping of filament is in good agreement with the previous available experimental and numerical results.Copyright