variavel0=<b>Timóteo Fernandes de Souza</b> - timoteo@em.pucrs.br DEM/FENG/PUC-RS
<b>Jorge Hugo Silvestrini</b> - jorgehs@em.pucrs.br DEM/FENG/PUC-RS
<b>Abstract.</b> The near wake behind two cylinders with different gaps arrangement is investigated through direct numerical simulation in two-dimensional configuration. For the representation of the obstacles, the immersed boundary technique is employed. Such a method consists in the imposition of a no-slip boundary condition within the flow field by the use of a specific forcing term added to the momentum equation. This method is coupled with an high-accurate numerical Navier-Stokes code written for DNS and LES in Cartesian grids. The sixth-order compact finite difference scheme is employed in the approximation of the spatial derivatives, providing an improved representation in the large range of scales present in unsteady flows. Time integration is performed with a third-order lowstorage Runge-Kutta method. The incompressibility condition is ensured with a fractional step method via the resolution of a Poisson equation for the pressure. In the present paper is investigated the wake development and interaction behind cyllinders obstacles located perpendicularly to the mean flow direction for different gaps arrangement. We are interested in the different instabilities modes of the two-cylinders arrangement at moderate Re numbers. Results based on the Strouhal number, as well as mean statistics are presented. From coherent vortex dynamics analysis made of movies of instantaneous vorticity field pictures taken during the simulation, it was possible to identify the in-phase, anti-phase and asymmetric vortex shedding modes and find the parameters that control the different instabilities modes.
<b>Keywords.</b> Vortex shedding, Direct numerical simulation, Immersed boundary method, Transition, Turbulence.