This article presents a computational model to simulate
the fluid interaction with moving flexible thin structures. The
model is based on a combination of three numerical approaches,
(i) a Lattice-Boltzmann solver for the flow equations, (ii) a
finite difference method to solve the solid equation, and (iii)
an Immersed Boundary Method (IBM) to model the coupling
between the fluid and the solid. The present IBM, based
on a direct-forcing approach, preserves the no-slip boundary
condition at the interface fluid-solid, and allows using
Cartesian uniform lattice encompassing both fluid and solid
domains. The flexible solid is modelled as an elastic structure.
The resulting governing equation involves thus tension and
bending forces as internal forces, the inertial and gravity forces
and finally the action of the fluid represented by the IBM forcing.
The method is first validated with reference to an academic
test case dealing with numerical simulations of a flapping flag
in a free stream. The model shows results in good agreement
with the published academic test case. The validation extends to
the free motion of rag in a water tunnel and a qualitative comparison
is available against experimental data performed with Digital
Image Correlation (DIC). Finally, the present method is used to
simulate the behaviour of flexible rags in the presence of highly
rotating flows at high Reynolds number, as it is the case in stirred
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .