Structural dynamics and aerodynamics measurements of biologically inspired flexible flapping wings

Abstract

Flapping wing flight as seen in hummingbirds and insects poses an interesting unsteady aerodynamic problem: coupling of wing kinematics, structural dynamics and aerodynamics. There have been numerous studies on the kinematics and aerodynamics in both experimental and computational cases with both natural and artificial wings. These studies tend to ignore wing flexibility; however, observation in nature affirms that passive wing deformation is predominant and may be crucial to the aerodynamic performance. This paper presents a multidisciplinary experimental endeavor in correlating a flapping micro air vehicle wing's aeroelasticity and thrust production, by quantifying and comparing overall thrust, structural deformation and airflow of six pairs of hummingbird-shaped membrane wings of different properties. The results show that for a specific spatial distribution of flexibility, there is an effective frequency range in thrust production. The wing deformation at the thrust-productive frequencies indicates the importance of flexibility: both bending and twisting motion can interact with aerodynamic loads to enhance wing performance under certain conditions, such as the deformation phase and amplitude. By measuring structural deformations under the same aerodynamic conditions, beneficial effects of passive wing deformation can be observed from the visualized airflow and averaged thrust. The measurements and their presentation enable observation and understanding of the required structural properties for a thrust effective flapping wing. The intended passive responses of the different wings follow a particular pattern in correlation to their aerodynamic performance. Consequently, both the experimental technique and data analysis method can lead to further studies to determine the design principles for micro air vehicle flapping wings.

Effect of the stiffness, inertia and oscillation kinematics on the thrust generation and efficiency of an oscillating-foil propulsion system

“…Similar results were found experimentally by Barannyk et al (2012). However, other works (Heathcote and Gursul, 2007;Michelin and Llewellyn Smith, 2009;Ramananarivo et al, 2011;Spagnolie et al, 2010;Wu et al, 2011) have shown that under certain conditions more rigid foils actually achieve higher performance. Generally, in these works, it was found that the best performance is achieved when the degree of flexibility is chosen so that the passive deformation occurs at the appropriate phase with respect to the driven motion (Ramananarivo et al, 2011;Spagnolie et al, 2010) or provides the greatest amplification of the input motion (Michelin and Llewellyn Smith, 2009).…”

Aerodynamics and dynamic stability of micro-air-vehicle with four flapping wings in hovering flight

“…For example, extensive experimental and numerical studies have been conducted on the effects of wing geometrical [14][15][16] (including wing aspect ratio, area, span et al) and on both lift and power consumption. Wing passive deformations beneficial for lift augment and power efficiency enhancement have also been discovered [17][18][19][20]. Then, various MAV prototypes using gear transmission, piezoelectric as well as electromagnetic drives were built, such as Robobee [21] of Harvard University, hummingbird [22] of AeroVironment Inc., KU Beetle [23] of Konkuk University, and Colibri [24] of ULB.…”

Improving the Fabrication Process of Micro-Air-Vehicle Flapping Wings

“…The hand-layup technique used in this study was subsequently extended to a flapping platform [20], tested experimentally, and compared with a computational model [21]. This manufacturing process was also adopted in an experimental investigation of the deformation during flapping [22], recovering the importance of flexibility in the production of aerodynamic thrust force. Many studies use a similar fabrication process, using carbon fiber skeletons with a thin membrane constructed with a combination of handassembled and commercially available parts [23][24][25][26][27][28][29][30].…”