Non-sinusoidal forms of effective angle of attack variation and multiple vortex formations for a pitching and plunging airfoil

Non-sinusoidal form of the effective angle of attack variation for a pitching and plunging airfoil is investigated using the Digital Particle Image Velocimetry (DPIV) technique to observe multiple vortex formation which degrades performance significantly in regimes of high thrust. A detailed categorization of separated vortex structures from the leading and trailing edges of a SD7003 airfoil was already performed in the Strouhal number range of 0.4 ≤ St ≤ 0.8 where sinusoidal forms of the effective angle of attack variation was observed. It is concluded that the Strouhal number is not the only parameter for the non-sinusoidal form of the effective angle of attack variation and there exists a threshold for the maximum effective angle of attack value, below where additional components at higher frequency appear. In this study, the occurrence of multiple vortex formations caused by non-sinusoidal form of effective angle of attack variation is investigated based on the classification of flow structure categories at a low Reynolds number range which is typical of small birds and potential MAVs.