Towards a fundamental understanding of low reynolds number flapping wing aerodynamics
Experimental studies were conducted by flapping a rigid rectangular wing with a mechanism that was capable of emulating complex insect wing kinematics including figure of eight motion, in order to explore the fundamental unsteady flow on a flapping wing at MAV scale Reynolds numbers. Force and moment measurements were obtained from a miniature six-component force transducer installed at the wing root. The wing was flapped in air and vacuum at the same frequency and wing kinematics and the resultant forces were subtracted in order to obtain the pure aerodynamic forces. In the first part of this paper, forces produced on the wing undergoing single degree-of-freedom fixed-pitch pure flapping motions (no pitching or out-of-the-plane coning motions) were determined for a variety of pitch angles. The unsteady aerodynamic coefficients measured during these tests were almost six times the steady state values measured in the wind tunnel. Flow visualization and particle image velocimetry (PIV) tests were also conducted, which showed that the key reason for the force increase on the flapping wing is due to a strong leading edge vortex whose strength varied throughout the flapping cycle. In the second part of the paper complete three degree-of-freedom (flapping, pitching, and coning) insect wing kinematics were investigated for different pitching and coning variations. The aerodynamic forces obtained in these tests were compared with coefficients obtained from the simple flapping tests and wind tunnel tests. 2012 AIAA.