Hydraulics and Hydraulic Machinery Department,

The purpose of the present numerical study is to assess a relatively rough, but quick way, to estimate the forces acting on an experimental model of the Achard cross-flow turbine that is to be tested in an aerodynamic wind tunnel. Under normal conditions, the Achard turbine runs in water, but in order to ac-curately investigate the flow field inside the turbine, an experimental set-up of a 1:1 geometric scale model has to be built, and measurements have to be per-formed in a wind tunnel (at such a scale, the model would require a huge channel if tested in water). Building the model in itself requires at least an ap-proximate knowledge about the values of forces that will act upon it during the experiments; such values can be obtained conveniently through numerical simulations. Using COMSOL Multiphysics 3.3a software, a 2D numerical study of the unsteady flow inside the Achard turbine has been performed, both for water and air (the latter based on criteria derived for such a case of similitude). The computed dynamic forces for a horizontal cross-section of the turbine agree well with experimental data available for twin cases, and could be used, in the sequel, to compute roughly the forces acting on the turbine experimen-tal model