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The two-dimensional laminar flow over a simultaneously pitching-heaving teardrop airfoil is studied numerically. The influence of frequency and amplitude on the wake structure and aerodynamic performance is investigated at a constant Reynolds number, Re=2640. The computational modeling accurately depicts the changes in the wake structure that occur between the von Karman, reverse von Karman and deflected conditions. Investigations at low flapping frequencies and amplitudes identified the presence of additional wake structures that had not been reported previously. The interaction between the flapping frequency and vortex shedding frequency appears to govern the formation of such multiple vortex wakes. The wake structures identified are presented in the form of a wake map where the transitions between the wake structures are visible. This study correlates the wake arrangement with the variation in force coefficients and explains why the presence of a reverse von Karman street is necessary but not a sufficient condition for thrust production. The time history of the drag coefficient and the phase relation between lift and drag show the dynamics of the wake. The variation of force coefficients and efficiency at different flapping conditions is evaluated, and the influence of flapping parameters is assessed. The underlying vortex interactions that influence the aerodynamic performance are identified. The development and distribution of stress fields developed due to periodic fluctuations behind the flapping airfoil have not been discussed previously. The velocity fluctuations in the wake due to the periodic flapping are presented, and regions of maximum stress distribution are identified. [ABSTRACT FROM AUTHOR]

The flapping kinematics have revealed a new paradigm of locomotion which is highly maneuverable and efficient compared to traditional propulsion systems. This work numerically investigates a three-dimensional wing undergoing pitching oscillations using Large eddy simulation (LES). The wake structure is presented using the Q -function, and the influence of pitching frequency on the structure of the wake is discussed. The vortices appear to travel as interconnected vortex rings in the bifurcated wake and are completely different from the two-dimensional investigations. The increase in pitching frequency ( St D) generates the interlinking structures between the two limbs of the bifurcated wake. The interlinking between the two limbs increases with St D and will get disrupted at sufficiently high St D . The increase in St D increased the force generated by the pitching wing, and the periodic dynamics between the force coefficients slowly transformed to quasi-periodic dynamics. The transition to quasi-periodic dynamics has not reduced the force generation of the pitching wing. The disruption of interlinking structures between the two limbs enhanced the lift generated by the pitching wing. The present investigation shows that the wake vortex structure strongly depends on St D . The generation of a jet in the wake is visible in the mean velocity profile indicating the thrust developed by the wing. The formation of multiple peak profiles indicated the formation of multiple jets, which resulted in enhanced thrust production. The Reynolds stress field generated from the velocity fluctuations appears to be influenced by both the pitching oscillations and vortex interactions. This study can guide the selection of better kinematic parameters to enhance the propulsive performance. [ABSTRACT FROM AUTHOR]