Flapping wings undergoing a reciprocating motion may encounter or ‘capture’ the wake fromprevious half-stroke, leading to local changes in the instantaneous aerodynamic force on thewing at the start of each half-stroke. Forces due to wake capture depend on estimation of theaerodynamic response of the wing to the combined wing motion due to the flapping kinematicsand the local velocity field in the wake. We develop here a simple approach to integratingprediction of wake capture effects into existing analytical models for insect flapping flight. Thelocal wake flow field is modelled as an additional induced velocity component normal to thestroke plane of the flapping motion that is blended/switched in at the start of each half-stroke.Existing experimental/numerical evidence suggests that wake capture effects are limited to thefirst 20% of each half-stroke. The magnitude of the induced angle of attack due to local wakeinduced velocity is a variable that must be determined empirically, however it appearsreasonable a priori that it is bounded between ± , where is the induced angle of attackdue to globally induced wake velocity at the flapping stroke plane. Comparison of modelresults against experimental data in the literature shows that the proposed model is able tosuccessfully predict the form of changes in lift and drag due wake capture for a number ofdifferent wing kinematic test cases. Whilst there is some uncertainty due to empiricalestimation of the local induced angle of attack, the subsequent effect of changes in kinematicsis analytically exact. Sensitivity analysis shows that the form of the flapping angle time historyhas a significant effect on the magnitude of wake capture forces. Triangular flapping profilesthat retain high translational velocity right up to stroke reversal evoke a much larger effectfrom wake capture compared to sinusoidal. This result is significant because whilst triangularflapping profiles can be generated in the laboratory, the very high accelerations required incurhigh mechanical cost that prevents practical adoption in nature or engineered flapping flightvehicles.
展开▼
