The influence of leading-edge deflection on the stability of the leading-edge vortices

To examine the effect of leading-edge deflected angle (Formula presented.) on the stability of the leading-edge vortex, the three-dimensional flow field of a flapping wing is simulated by a numerical method. The multi domain mesh generation, dynamic mesh and large eddy simulation technology are employed to capture the finer flowfield structure. The wings perform pure periodic oscillations, and the Reynolds number (Re) is 4527 based on the chord length c. The folding line formed after the deflection coincides with the pitch axis and is located at the 1/4c from the leading edge. The results show that the increase of (Formula presented.) maintains the strength of the leading-edge vortex for longer time, and weakens the influence of the motion of the wing on the leading-edge vortex intensity. The flowfield topological analysis shows that the increase of (Formula presented.) also prevents the formation of secondary vortices between the wing surface and the leading-edge vortices, which indirectly contributes to the attachment of the leading-edge vortices to the wing. Moreover, the vortex dynamics equations have been analyzed, and the results indicate that the increase of (Formula presented.) will delay the occurrence of spanwise convection of vorticity and weaken its intensity. In addition, it can also suppress the spanwise flow behind the leading-edge vortices toward the symmetric plane. As a result, increasing (Formula presented.) stabilizes the boundary layer in this region and thereby stabilizes the leading-edge vortices indirectly. Finally, a new parameter is introduced to quantitatively evaluate the proximity of the leading-edge vortex to the surface of the plate. Our method comprehensively considers the influence of the leading-edge vortex scale and the core motion on the approaching of the leading-edge vortex to the wing, and some important conclusions on the developing law of the leading-edge vortex, which are agreement with the experimental measurement, are obtained.