Individual fibre in an arbitrary flow field - true direct numerical simulation (DNS) using an implicit immersed boundary method

Paper in proceeding, 2008

A novel immersed boundary method for three-dimensional, time-dependent flows is presented in this work and applied to simulating the behaviour of an individual fibre in various flow regimes. The fibre is placed in a periodic box and has either a fixed position or is allowed to move freely (including translation and rotation) through the domain. The immersed boundary method mirrors the velocity field along the normal of the local triangulated immersed boundary segment to guarantee that the fluid takes into account the immersed body accurately. As a result of the procedure, there is a fictitious velocity field inside the immersed boundary, mirroring the boundary layer. Care is taken to solve the velocity field in such a way that the mass is conserved in the cells containing the immersed boundary. The method applied is second-order accurate and is intended to be used for fully resolving the flow field around arbitrary moving bodies immersed in a fluid. The immersed boundary method is employed on a selection of different fibre shapes, aiming at predicting the behaviour of real fibres in realistic flow situations. The force exerted by the fluid is directly calculated by integrating the pressure and viscous forces over the objects immersed. The resulting coarse-grained drag and lift force functions can be employed in larger scale calculations of fluid-fibre flows.