Experimental investigation on the leading-edge vortex formation and detachment mechanism of a pitching and plunging plate

Li, Zhenyao; Feng, Li-Hao; Kissing, Johannes; Tropea, Cameron; Wang, Jinjun

doi:10.1017/jfm.2020.509

Cited by 28 publications

(23 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The alternative positive/negative bands upstream of the LEV correspond to the secondary vortices that form near the leading edge of the wing (Li et al. 2020). Figures 11( a , b ) show that the LEV of the rigid case moves downstream at roughly the same velocity at both spanwise positions, and 0.6.…”

Section: Resultsmentioning

confidence: 99%

Fluid–structure resonance in spanwise-flexible flapping wings

et al. 2023

View full text Add to dashboard Cite

We report direct numerical simulations of the flow around a spanwise-flexible wing in forward flight. The simulations were performed at $Re=1000$ for wings of aspect ratio 2 and 4 undergoing a heaving and pitching motion at Strouhal number $St_c\approx 0.5$ . We have varied the effective stiffness of the wing $\varPi _1$ while keeping the effective inertia constant, $\varPi _0=0.1$ . It has been found that there is an optimal aerodynamic performance of the wing linked to a damped resonance phenomenon, that occurs when the imposed frequency of oscillation approaches the first natural frequency of the structure in the fluid, $\omega _{n,f}/\omega \approx 1$ . In that situation, the time-averaged thrust is maximum, increasing by factor 2 with respect to the rigid case with an increase in propulsive efficiency of approximately 15 %. This enhanced aerodynamic performance results from the combination of larger effective angles of attack of the outboard wing sections and a delayed development of the leading edge vortex. With increasing flexibility beyond the resonant frequency, the aerodynamic performance drops significantly, in terms of both thrust production and propulsive efficiency. The cause of this drop lies in the increasing phase lag between the deflection of the wing and the heaving/pitching motion, which results in weaker leading edge vortices, negative effective angles of attack in the outboard sections of the wing, and drag generation in the first half of the stroke. Our results also show that flexible wings with the same $\omega _{n,f}/\omega$ but different aspect ratio have the same aerodynamic performance, emphasizing the importance of the structural properties of the wing for its aerodynamic performance.

show abstract

Section: Resultsmentioning

confidence: 99%

Fluid–structure resonance in spanwise-flexible flapping wings

et al. 2023

View full text Add to dashboard Cite

show abstract

“…The determination of this threshold is based on the work of Li et al. (2020). The position of the vortex centre is determined by the criterion proposed by Graftieaux, Michard & Nathalie (2001).…”

Section: Basic Flow Situation and Criterion Of Critical Momentsmentioning

confidence: 99%

“…Li et al. (2020) found that with the change in the maximum effective angle of attack, different secondary vortex structures lead to the shedding of DSV. Li et al.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Critical indicators of dynamic stall vortex

Xiao

Feng

2022

J. Fluid Mech.

Self Cite

View full text Add to dashboard Cite

During a dynamic stall process, various flow structures leave their pressure footprints on a wing surface, through which it is possible to understand the development of different flow stages and predict the critical flow events. Based on a classical airfoil ramp-up pitching motion, proper orthogonal decomposition analysis of pressure on the suction surface is carried out in this study. Accordingly, the surface pressure evolution during dynamic stall is summarized into three basic physical schemas, based on which several real-time critical indicators for predicting the flow events related to the dynamic stall vortex (DSV) are constructed. These critical indicators include the spatial distribution coefficient of pressure (SDCP), the high-order central moment of pressure (HCMP), the location of peak pressure (LPP) and the modulated location of peak pressure (MLPP). These indicators can predict the formation of laminar separation bubbles, DSV initiation, DSV centre position and the detachment of DSV. Therefore, the real-time whole-life monitoring of DSV has been realized. Moreover, the effectiveness of these indicators has also been confirmed under different parameters, and testing using wind tunnel experimental data proves their noise robustness. Studies show that the SDCP and HCMP may also be effective even if only two transducers are used. Finally, a modification method of SDCP based on Z-score standardized pressure is proposed. It is found that the modified SDCP can effectively reduce sensitivity to kinematic parameters and the Reynolds number. The critical indicators in this study can be used as a reference for the standardized mathematical and physical description of DSV evolution, thus laying a foundation for constructing a universal theoretical framework of dynamic stall.

show abstract

“…In contrast to the original airfoil, the connection between the leading edge shear layer and the DSV is weaker for the TEF airfoil (Figure 18(d)). When the connection between the leading edge shear layer and the DSV is weak, it means that the DSV no longer accumulates vorticity from the leading edge shear layer [27]. Due to the lack of vorticity supply from the leading edge shear layer, the strength of the DSV decreases rapidly.…”

Section: Analysis Of the Circulation And Vortexmentioning

confidence: 99%

Trailing Edge Flap Effects on Dynamic Stall Vortex and Unsteady Aerodynamic Forces on a Pitching Airfoil

Xing

Zhang

2022

International Journal of Aerospace Engineering

View full text Add to dashboard Cite

This study focuses on the effect of the upward deflection of trailing edge flap (TEF) on the strength and trajectory of dynamic stall vortex (DSV) around a pitching airfoil by means of numerical simulations based on unsteady Reynolds-averaged Navier-Stokes (URANS). The effect of the upward deflection of the TEF on the unsteady aerodynamic forces due to DSV is analyzed. The numerical simulation method for large mesh deformation is constructed. Radial basis function- (RBF-) based mesh deformation algorithm, as well as Laplacian and optimization-based mesh smoothing algorithm, is adopted to ensure the mesh quality in flow field simulations. The results reveal that the upward deflection of the TEF can reduce the peaks of drag and pitching moment coefficients. Although the maximum lift coefficient of the airfoil is slightly reduced, its maximum drag and pitching moment coefficients are significantly reduced by up to 34.8% and 31.8%, respectively. The vorticity transport behavior in a planar control region during the DSV formation and detachment is analyzed. It is found that the TEF can change the development process of the DSV. The upward deflection of the TEF reduces the vorticity flux from the leading edge shear layer, which causes the circulation of the DSV and the translational velocity of the vortex center to decline. The peaks of the unsteady aerodynamic forces on the airfoil induced by the DSV are reduced. The upward deflection of the TEF plays the role of alleviating the pitching moment load. The longer TEF can result in a better control effect. The bigger the upward deflection angle of the TEF, the better its control effect.

show abstract

Experimental investigation on the leading-edge vortex formation and detachment mechanism of a pitching and plunging plate

Abstract: Abstract

Cited by 28 publications

References 38 publications

Fluid–structure resonance in spanwise-flexible flapping wings

Fluid–structure resonance in spanwise-flexible flapping wings

Critical indicators of dynamic stall vortex

Trailing Edge Flap Effects on Dynamic Stall Vortex and Unsteady Aerodynamic Forces on a Pitching Airfoil

Contact Info

Product

Resources

About