Vorticity dynamics and stability of the leading-edge vortex on revolving wings

An aspect ratio 9.5 rectangular wing is articulated in revolving and translating motions at a 45° angle of incidence and Reynolds number Re=O(300). The effects of rotational (Coriolis and centripetal) accelerations and relative inflow velocity profile on vorticity transport within the leading-edge vortex (LEV) system are independently investigated. For the range of displacements studied (180° rotation and corresponding translational displacement), a stably attached leading-edge vortex (LEV) is observed when rotational accelerations and/or a linearly varying inflow velocity profile is present; however, the inflow velocity profile has a stronger effect on stability of the LEV. LEV vorticity magnitude and lift are significantly augmented when both factors are included (i.e., the full revolving wing case). Vorticity transport analyses are conducted in a planar control region two chords from the axis of rotation, where LEV stability is typically observed on revolving wings at high incidence and at an equivalent spanwise position in the translating case. The fully revolving wing case exhibits a substantially larger leading-edge shear-layer vorticity flux than the other cases, whereas Coriolis tilting makes little contribution to regulation of LEV strength. A correlation is found between the spanwise convective flux and tilting flux contributions in all cases. Decomposition of the spanwise convective flux term demonstrates that the two phenomena are kinematically linked and, together, define a new out-of-plane convective flux term that captures the essence of the spanwise convective flux. The role of this term and the effect of rotational accelerations on it are examined.

Inflow-velocity and rotational effects on revolving and translating wings

Paulson,

Jardin,

Buchholz

2023

Effects of wing loading on the aerodynamic characteristics of autorotating maple seeds

Liu,

Wang,

Zeng

et al. 2024

Natural maple seeds can fall into stable autorotation when descending. Their excellent aerodynamic performance can be applied to biomimetic aircraft design. Wing loading plays an important role in flight performance. To make clear the effects of wing loading on the aerodynamic characteristics of autorotating maple seeds, experiments integrated with numerical simulation were performed. In the experiment, the free fall test and the wind tunnel test were conducted on maple seeds with variable wing loadings. During the free fall process, four typical stages can be divided for the maple seed according to different kinematic characteristics. In the numerical simulation, the Moving Reference Frame method was used to simulate the fluid of autorotating maple seeds. Both experiment and simulation results show that descending velocities and spinning rates rise almost linearly with the increase in wing loadings, and descending velocity is closely related to spinning rate. Obvious leading-edge vortexes were observed on seed wing, which are the flow mechanism of high lift. The pressure differences between the top and lower surfaces of seeds grow with increasing wing loadings. Larger wing loadings lead to more serious separation of leading-edge vortex. The parameter influence analysis demonstrates that smaller conning angles or larger spinning rates are beneficial for high-lift flight. The spinning rate has a more significant effect on the autorotating maple seeds. However, when the spinning rate is larger than 200 rad/s, the lift does not increase anymore. The spinning rate should be controlled smaller than 200 rad/s when applied to biomimetic aircraft.

The lift enhancement mechanism caused by the deformation of the surface of the wide-speed waverider

Qu,

Wang,

Zhao

et al. 2024

The optimization method provides an effective approach to enhance the low-speed lift of the vortex lift waveriders by deforming the aerodynamic shape refinedly. However, the vortex lift enhancement mechanism of the optimized configuration is unclear. In this study, the flow evolutions of the original and the optimized configurations are studied by employing the delayed detached-eddy simulation. Results indicate that the convex deformation of the leeward surface plays a dominant role in enhancing the vortex lift by enhancing the low-pressure suction at the upstream breakdown location and delaying the vortex breakdown. For the enhancement of the low-pressure suction, the convex deformation intensifies the streamwise vorticity below the axis of the primary vortex of the leading-edge vortex, in turn enhancing the downwash effect and causing the primary vortex to move downward. This reduces the pressure coefficient induced by the primary vortex on the leeward surface, thus enhancing the vortex lift. In terms of the delay of the vortex breakdown, the convex deformation compresses and accelerates the flow between the spanwise convex and the leading edge. These intensities enhance the washing effect along the spanwise direction on the outward wing and cause the primary vortex to deflect toward the outboard wing. Subsequently, the primary vortex and the shedding vortices generated by the shear layer instability merge, which increase the primary vortex intensity, and enhance the streamwise velocity in the vortex axis. Correspondingly, the primary vortex breakdown is delayed. Ultimately, the increased low-pressure region caused by the delay of the vortex breakdown enhances the vortex lift.