  Natural swimmers usually perform undulations to propel themselves and perform
a range of maneuvers. These include various biological species ranging from
micro-sized organisms to large-sized fishes that undulate at typical kinematic
patterns. In this paper, we consider anguilliform and carangiform swimming
modes to perform numerical simulations using an immersed-boundary methods based
computational solver at various Reynolds number regimes. We carry out thorough
studies using wavelength and Strouhal frequency as the governing parameters for
the hydrodynamic performance of undulating swimmers. Our analysis shows that
the anguilliform kinematics achieves better hydrodynamic efficiency for viscous
flow regime, whereas for flows with higher Reynolds number, the wavelength of
the wavy motion dictates which kinematics will outperform the other. We find
that the constructive interference between vortices produced at anterior parts
of the bodies and co-rotating vortices present at the posterior parts plays an
important role in reversing the direction of Benard-von Karman vortex street.
Since most of the thrust producing conditions appear to cause wake deflection;
a critical factor responsible for degrading the hydrodynamic efficiency of a
swimmer, we discuss the underlying mechanics that would trigger this
phenomenon. We demonstrate that the choice of kinematic and flow conditions may
be restricted for the natural swimmers due to their morphological structures,
but our findings provide a guideline on their selection for bio-inspired
underwater vehicles.
