Intermittency behaviour in the flow past an oscillating airfoil

The flow over a plunging airfoil is investigated by means of a Navier-Stokes solver at a Reynolds number of 1, 000. A parametric analysis by varying the plunge amplitude (h) at a fixed frequency (k = 2) revealed the presence of a new flow dynamics for a flapping airfoil. For h > 0.91, the dynamics is characterized by long intervals of periodicity with abrupt chaotic intervals for short durations. The occurrence of such chaotic intervals increases as the amplitude is increased and finally, the flow field becomes chaotic for the entire time history. This type of dynamical behaviour where irregular chaotic intervals appear in between periodic intervals is known as intermittency. We use time series analysis techniques such as phase space reconstruction and recurrence plots to establish the presence of intermittency. Recurrence plot is an excellent tool for analysing phase space trajectories since it provides good insights into the system dynamics even with a short time series.