Numerical and experimental analysis of tandem flapping flight

Flapping-wing Micro Aerial Vehicles (FMAVs) are equipped with a fixed tail that is primarily used for the achievement of stability and controllability of the vehicle. However, previous research has revealed that the interference between the wake of the upstream flapping wings and the tail is complex and can affect the performance of the FMAVs considerably. Hence, the current study investigates the interaction between a plunging wing and a stationary tail, in a combined experimental and numerical study. The Reynolds numbers tested are 5,000 and 10,000. The experiments were performed in a water channel, varying the separation distance between the flapping airfoil and the tail, as well as the angle of attack of the tail airfoil. Time-resolved 2D velocity fields were captured via Particle Image Velocimetry (PIV) technique, to characterize the flow field. In addition, the flow is numerically simulated by use of an Immersed Boundary Method (IBM) solver, to enable comparison to the experimental results. 3D simulations involving wings of finite span and end plates have also been performed, to more accurately replicate the actual experimental setup and to investigate the possible influence of the approximation of 2D flow. Comparison between the same configuration at Reynolds number at 5,000 and 10,000 shows that their vorticity contour plots are very similar. Next, experimental and numerical simulations show that although both 2D and 3D simulations show good correlation with the experiments qualitatively, 3D simulations resemble the experiments better than the 2D simulations, indicating that 3D effects are present in the experiments. Lastly, the study shows that the angle of attack of the tail and the flapping wing-tail distance have significant effects on the performance of an FMAV. Increasing the angle of attack of the tail increases its lift and drag simultaneously, but the percentage increase is higher for the lift than the drag. The understanding obtained from these results will be supportive to the design of FMAVs.