Effects of local oscillation of airfoil surface on lift enhancement at low Reynolds number

Kang, Wei; Pengfei, Lei; Zhang, Jiazhong; Xu, Min

doi:10.1016/j.jfluidstructs.2015.05.009

Cited by 26 publications

(5 citation statements)

References 35 publications

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“…At this time, the lift coefficient value of the airfoil can still be stably increased. In both papers [22][23][24], the internal physical mechanism of active vibration wall that enhances the anti-separation ability of the fluid on airfoil surface is discussed. When the airfoil deforms to Figure 28a, the lift coefficient starts to decrease when the free shear layer develops to the middle and rear sections of the airfoil.…”

Section: Active Deformation Airfoil At 18mentioning

confidence: 99%

Numerical Simulation of Unsteady Aerodynamic Performance of Novel Adaptive Airfoil for Vertical Axis Wind Turbine

et al. 2019

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The aerodynamic performance of the blade determines the power and load characteristics of a wind turbine. In this paper, numerical research of the active deformation of an airfoil with equal thickness camber line was carried out, which shows the great potential of this active flow control method to improve the flow field. The NACA0012 is taken as the reference airfoil, and the inflow wind speed is 9 m/s, the chord length of the airfoil is 0.4 m, and the Reynolds number is 2.5 × 105. The influence factors, such as deformation amplitude and deformation frequency on the aerodynamic performance, were studied at different attack angles before and after stall. Studies have shown that: firstly, at different angles of attack, different deformation amplitudes and frequencies have great influence on the aerodynamic performance of the active deformed airfoil. The active deformation can improve the aerodynamic performance of the airfoil in different degrees in deep stall and light stall regions. Secondly, a suitable deformation amplitude and deformation frequency can improve the aerodynamic performance of airfoil stably and effectively in light stall, which occurs when the deformation amplitude equals to 0.02c and the deformation frequency is lower than 2 Hz, and the maximum lift-drag ratio can be increased by about 25%. Before stall, when the deformation frequency is 2 Hz and amplitude is 0.10c, the airfoil will have a negative drag coefficient in the process of deformation, and the airfoil will produce a thrust which is similar to the energy capture of the flapping foil. This is an unexpected discovery in our research.

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Section: Active Deformation Airfoil At 18mentioning

confidence: 99%

Numerical Simulation of Unsteady Aerodynamic Performance of Novel Adaptive Airfoil for Vertical Axis Wind Turbine

et al. 2019

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“…As such, mechanistic insights into the surface morphing framework considered here could inform actuation protocols in these other settings. (Indeed, investigations of other surface-driven actuation strategies have reported aerodynamic performance benefits through lock-on effects [21], suggesting similar mechanisms prevail across these actuation technologies). Similarly, passively compliant actuators have shown potential utility in aerodynamic flow control [23][24][25][26][27], and insights into the desired structural dynamics obtained via prescribed motion could provide a means to back out material properties that would induce the desired fluid-structure interplay.…”

Section: Introductionmentioning

confidence: 99%

“…We emphasize that a broader class of surface-deformation based actuators have been developed for active flow control (see, e.g., Wiltse and Glezer [18], Seifert et al [19], Jeon and Blackwelder [20], Kang et al [21] and the review of Cattafesta III and Sheplak [22]). As such, mechanistic insights into the surface morphing framework considered here could inform actuation protocols in these other settings.…”

Section: Introductionmentioning

confidence: 99%

Surface morphing for aerodynamic flows at low and stalled angles of attack

Thompson¹,

Goza²

2021

Preprint

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In the current work we numerically study the effect of traveling-wave surface morphing actuation, which is a lightweight, spatially distributed actuation strategy made possible by advances in materials science. Although this actuation strategy has been studied at higher Reynolds numbers for an airfoil and a rectangular flat plate, its effects at low Reynolds numbers relevant to microair vehicles have not yet been investigated. We perform high-fidelity 2D numerical simulations to study the effects of traveling wave surface morphing on the suction surface of NACA0012 at Re = 1,000. The kinematics of actuation are defined by wavenumber and wavespeed, both of which are varied over a wide range of values to include parameters that considerably change the lift dynamics as well as those that do not. We first study the effect of actuation at an angle of attack of α = 5 • , where the unactuated flow is steady. The lift dynamics are found to align with the surface morphing kinematics, and there is a low-pressure minimum shown to be introduced into the flow-field by morphing that advects at a speed agnostic to the morphing parameters. Lift benefits are found to be maximal when the morphing kinematics align with this intrinsic flow speed. We then investigate the role of morphing in the presence of an unsteady, separated baseline flow (with intrinsic vortex-shedding processes) at α = 15 • . At this higher angle of attack, we identify three distinct behavioral regimes based on the relationship between morphing and the underlying shedding frequency. Of these regimes, the most beneficial to mean lift is the lock-on regime, where the vortex-shedding dynamics align with the morphing kinematics. Lock-on was similarly found using this actuation strategy at higher Reynolds numbers, though in that setting the effect was to reduce separation, whereas at these lower Reynolds numbers the outcome is that vortex shedding persists with-in certain cases-significant lift benefits. We also identify other regimes where morphing can become out of phase with the vortex-shedding dynamics, termed here the interactive regime, and where morphing leaves the unactuated dynamics unaltered, termed here the superposition regime. At the higher angle of attack, parameters leading to lift benefits/detriments are explained in terms of the effect of morphing on the leading and trailing-edge vortex. Where appropriate, connections between the mechanisms at the higher angle of attack are drawn to the matching/disparity of timescales between morphing and lift-producing pressure signatures seen in the lower-angle-of-attack setting.

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“…This method has the advantages of a simple structure, a wide frequency bandwidth, no need for air channels and easy miniaturization, but it still requires electric energy. (c) Vibration diaphragms: A blade with an elastic structure shows better adaptability to the flow field in many cases, and the deformation or vibration caused by the elastic material is often beneficial to the improvement of the flow field structure. However, the elastic surface is easily damaged under long‐term operation.…”

Section: Introductionmentioning

confidence: 99%

Influence of microcylinders with different vibration laws on the flow control effect of a horizontal axis wind turbine

Wang

Luo

et al. 2019

Wind Energy

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Due to the flow separation on the blade of the NREL Phase VI wind turbine, a new flow control technique involving installation of an off‐surface vibrating small structure is proposed. By considering the actual flow condition, fluid‐solid coupling is applied in which two kinds of microcylinder vibration modes are set up, and the aerodynamic performance is numerically studied. The influence of the vibration modes, amplitude, and frequency of the off‐surface vibrating small structure on the aerodynamic performance is explored. For various stall conditions, the flow separation can be well suppressed by utilizing a suitable vibrating microcylinder rather than a static microcylinder. In addition, the vibrating microcylinder shows a noticeable suppression effect on large flow separation. Both the vibration direction and vibration amplitude play leading roles in the improvement of the aerodynamic performance, and a microcylinder with a high vibration frequency can more quickly suppress surface flow separation to achieve an optimum aerodynamic performance than a microcylinder with a low vibration frequency. By setting microcylinders with suitable vibration rules close to the blade surface, the wind energy coefficient can be obviously increased compared with those obtained when adding a static microcylinder or without microcylinder addition.

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Effects of local oscillation of airfoil surface on lift enhancement at low Reynolds number

Cited by 26 publications

References 35 publications

Numerical Simulation of Unsteady Aerodynamic Performance of Novel Adaptive Airfoil for Vertical Axis Wind Turbine

Numerical Simulation of Unsteady Aerodynamic Performance of Novel Adaptive Airfoil for Vertical Axis Wind Turbine

Surface morphing for aerodynamic flows at low and stalled angles of attack

Influence of microcylinders with different vibration laws on the flow control effect of a horizontal axis wind turbine

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