Application of biologically inspired "Pop-Up'' feather style high lift device on micro aerial vehicles.
Wang, John Chung Hung.
Date of Issue2013
School of Mechanical and Aerospace Engineering
Recent years saw the increase in relevance of Micro Aerial Vehicle (MAV) in both civilian and military applications. One of the more attractive feature of MAV is the lower cost and ease of transport due to its smaller size; however, the size and weight of the MAV also limited the forms of high lift device that could be applied to the vehicle to increase its operating envelope. One of the devices proposed is the ``Pop-Up'' feather type passive high lift device (passive flap), a design based on observation of bird feathers during landing. The primary objective of the current research is to investigate the performance of passive flap when applied to the lower operating Reynolds number of MAVs (Re=40,000) and establish the CFD and experimental procedure for optimization of passive flap design for application on MAV. To that end, two simulation procedures were developed: one using steady-state solver and optimization algorithm to seek the equilibrium flap angle; the other directly solves for the movement of the flap based on forces acting on the flap and the flap inertia. The solutions from the resulting solvers agrees favorably with existing water tunnel experimental lift data for 2D airfoil with and without passive flap, and while the solutions were not fully validated for detailed flow features, they could be used to supplement the experimental data to better evaluate the impact of different flap size c_f and flap position x_f on the performance of the flap under 2D settings. On the other hand, it was recognized that three-dimensional flow features could have major impact on the performance of the flap, namely the wing-tip vortex which alters the effective angle of attack along the span of the wing. As no prior studies on the application of passive flap on finite wing existed, wind tunnel studies were performed at Re=40,000 on a rectangular wing model with varying size of flaps spanning from the center-line of the wing b_f; finite wing simulations were also performed to obtain visualization on flow structure around the wing, though further validation of the 3D results needs to be left for future work. It should be noted that there remains outstanding issues to be addressed in the future. Some anomalous results show that the numerical discretization requires a body fitted mesh in the near wall region and further validation work is required to assert accuracy. While some mean aerodynamic characteristics may agree well between the numerical and experimental results, the computed detailed flow behavior along the airfoil surface regions will require further validation. In particular, the experimental diagnostics were only limited to measurements of the integrated quantities of lift.