Investigations into transient wakes behind a custom airfoil undergoing pitching motion.

The wake dynamics behind a sinusoidally pitching custom designed symmetrical airfoil is analyzed computationally. The effect of pitching frequency and pitching amplitude is investigated independently at a constant Reynolds number. The wake patterns are found to exhibit a transition from von Karman to reverse von Karman vortex street and from symmetric reverse von Karman vortex street to asymmetric deflected wake as established. For laminar flow under investigation, the contours of time-varying velocity fluctuations are presented. The mean profiles of velocity and the fluctuations at different locations in the wake show that the thrust wakes are generated at the expense of energy of the surrounding fluid. The temporal behavior of the flow field is analyzed using the phase plot. The time series plots of force coefficients show a periodic loading on the airfoil. Proper orthogonal decomposition (POD) analysis of drag, neutral and thrust wakes displayed the evolution of coherent structures in the flow field. The evolution of these structures portray the transitions in the wake of the airfoil. The merging of coherent structures in an asymmetric deflected wake turns out to be an efficient way of identifying the location of deflection. • The vortex pairing mechanism is identified for the deflected wake. • The time average of fluctuating quantities are evaluated to quantify flow field. • The chaotic behavior of the flow field is identified using the u − v phase plot. • Time series analysis shows the effect of frequency is more prominent on force coefficients. • The coherent structures are identified using Proper orthogonal decomposition. [ABSTRACT FROM AUTHOR]