Effect of Wing Flexibility on Lift and Thrust Production in Flapping Flight

摘要

In bird and insect flight, wing deformation plays an important role in aerodynamic performance. The wingndeformation is produced by neuromuscular control and/or by aeroelastic effects. The focus of the current study is tonevaluate the effects of wing deformation by coupling a large-eddy simulation solver with a linear elastic membranenmodel. Different membrane prestresses are investigated to give a desired camber in response to the aerodynamicnpressure. All simulations are carried out at Re u0001 10; 000 for forward flight with an advance ratio of 0.5. The resultsnshowthat the camber introduced by a flexiblewing increases the thrust and lift production considerably.An analysisnof flow structure reveals that, for flexible wings, the leading-edge vortex stays attached on the top surface of the wingnand glides along the camber and covers amajor part of thewing,which results in high force production.On the othernhand, for rigid wings, the leading-edge vortex lifts off from the surface resulting in lower force production. Further,nintroduction of the camber also increases the force component contributing to thrust, leading to a high thrust-to-liftnratio. In comparison to a rigidwing, a 40%increase in thrust is observed for the low-prestress case,which results in ancamber of 0.25 chord. Further, the results also show that the wing with high spanwise prestress and low chordwisenprestress offers better performance both in terms of force production and uniformity in the force-induced cambering.