When a bluff body is located in a uniform flow, the flow is separated and vortices are
formed. Consequently, the vortices cause “flow-induced vibrations”. Especially, if the Strouhal
number and the frequency of the body oscillation coincide with the natural frequency, the lock-in
regime will occur and we could find the large damages on it. Therefore, it is profitable, in engineering
problems, to clarify this phenomenon and to suppress the vibration, in which the effect of elastic walls
on the suppression is focused. Then, the aims of this article are to clarify the oscillatory characteristics
of the elastic body and the flowfield around the body by numerical simulations, in which a square
pillar with elastic walls is set in a uniform flow. Two dimensional incompressible flows are solved by
the continuity equation, Navier-Stokes equation and the Poisson equation which are derived by taking
divergence of Navier-Stokes equation. Results show that a small deformation of elastic walls has a
large influence on the body motion. In particular, the effect is very distinct at the back.