The Performance and Force Coefficients of Flapping Foil

The added mass and damping coefficients of a flapping foil propulsor are investigated using an URANS method with the k-omega turbulence model for two Reynolds numbers. First, computed performance coefficients are compared with experimental results from the open literature. Even though the flow regime is not exactly the same, reasonably good agreement was found between the current and published results. Then, the foil forces are evaluated in terms of added mass and damping coefficients. The viscous added mass and damping components are determined using an approximate first order harmonic fitting. The coefficients were parametrized using theoretical angle of attack and Strouhal number. They were determined in two coordinate systems, i.e. in the inertial and body-fixed coordinate ones. The choice of coordinate system does not have considerable influence in the parametrization of the added mass coefficient. However, the contours of constant damping coefficient were slightly different in the parametric space. A particular case is analyzed in more detail for two Reynolds numbers. Flow features like separation are shown how to affect added mass coefficients. The separated flow seems to reduce the performance of the foil.