Ground effects on the stability of separated flow around a NACA 4415 airfoil at low Reynolds numbers

He, Wei; Li, Larry K.B.

doi:10.1016/j.ast.2017.10.039

Cited by 26 publications

(13 citation statements)

References 44 publications

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“…Two different classes of instability modes can be identified: 1) two-dimensional traveling KH modes (denoted by hollow markers), for which Sr > 0; and 2) three-dimensional stationary global modes (denoted by filled markers), for which Sr 0 (not plotted). As mentioned earlier, similar modes have been identified before in both steady [24] and unsteady [20] separated flows around an airfoil with [26] and without [23,32] the ground effect. However, in contrast to those earlier studies, in which the KH Fig.…”

Section: B Stability Analysissupporting

confidence: 80%

“…However, these three-dimensional stationary modes have recently been found to be less unstable than the twodimensional KH mode [23]. A similar conclusion was reached by He et al [26], who analyzed both the primary and secondary instabilities of the unsteady separated flow around a NACA 4415 airfoil at 300 ≤ Re ≤ 1000 and α 20 deg. The airfoil was positioned at a nondimensional height (based on the chord length) of 0.2 ≤ H ≤ ∞ above two different types of flat ground: a stationary ground and a moving ground.…”

supporting

confidence: 58%

“…As mentioned earlier, the KH mode is stable at this Reynolds number (Re 200). However, a recent work by He et al [26] on the separated flow around a NACA 4415 airfoil above a flat ground has shown that, when the Reynolds number exceeds roughly 500, the KH mode becomes unstable, destroying the steady separation bubble behind the airfoil and producing large-scale vortex shedding downstream at a well-defined frequency. Thus, at higher values of Reynolds number, the KH mode is expected to cause the airfoil wake to transition from a spatial amplifier of extrinsic perturbations to a self-excited oscillator with an intrinsic natural frequency [33].…”

Section: B Stability Analysismentioning

confidence: 99%

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Stability of Low-Reynolds-Number Separated Flow Around an Airfoil Near a Wavy Ground

Guan

Theofilis

et al. 2019

AIAA Journal

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In this numerical-theoretical study, a linear BiGlobal stability analysis of the steady massively separated flow around a NACA 4415 airfoil was performed at a low Reynolds number (Re 200) and a high angle of attack (α 18 deg) close to a wavy ground, with a focus on the effect of three different types of stationary roughness: 1) a perfectly flat ground, 2) a wavy ground with small-amplitude undulations, and 3) a wavy ground with large-amplitude undulations. On increasing the undulation amplitude h 0 of the ground but keeping the mean ground clearance constant, it was found that the lift coefficient increased owing to an increase in the static pressure under the airfoil, which is reminiscent of the conventional ground effect over a flat surface. However, it was also found that the leading flow perturbation was the three-dimensional stationary global mode and not the two-dimensional traveling Kelvin-Helmholtz mode, contrary to the results of previous analogous studies of linear global instability of massively separated flow away from the ground. This study provides new insight into the stability of airfoil-ground flow systems at a low Reynolds number and a high angle of attack, contributing to a better understanding of the ground-effect aerodynamics of small insects and micro air vehicles flying over rough waters or complex terrain.

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Section: B Stability Analysissupporting

confidence: 80%

supporting

confidence: 58%

Section: B Stability Analysismentioning

confidence: 99%

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Stability of Low-Reynolds-Number Separated Flow Around an Airfoil Near a Wavy Ground

Guan

Theofilis

et al. 2019

AIAA Journal

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“…He et al. 3 studied the flow separation of the NACA4415 airfoil at 20° angle of attack at low Reynolds number close to the ground, and concluded that the ground effect has an obvious effect on the flow separation. Wu and Zhao 2 studied the ground effect of the NACA0012 rigid flapping airfoil.…”

Section: Introductionmentioning

confidence: 99%

“…So far there have been many studies on the ground effect of airfoil and fluid–solid interaction of flexible thin plates and airfoils. 2–18 Previous studies have shown that the presence of ground effects can lead to an increase in lift, and flexible airfoils and thin plates generally have better locomotion performance over rigidity. However, no work has systematically studied the effect of flexibility changes on the characteristics of the force and deformation of the flexible wing.…”

Section: Introductionmentioning

confidence: 99%

Analysis of fluid and solid interaction of the flexible bionic wing in ground effect

Zhu

Cao

Xin

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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Animals can obtain excellent locomotion performance as they swim or fly under ground effect in nature. Inspired by this, fluid mechanisms of the flexible bionic wing oscillating and gliding in ground effect are investigated by fluid–solid interaction simulation in this study, respectively. For the oscillation motion, the flexible wing vertically moves up and down at different distances from the ground. Different parameters such as the average height from the ground, oscillation frequency of the flexible bionic wing, and airfoil flexibility are considered in the simulation. At the same time, the gliding motion of the flexible wing in the ground effect is also studied, compared with the oscillation motion. Several simulations are set for different parameters. The characteristics of the force and deformation of the flexible wing and the flow field around the flexible wing are analyzed in depth. The effects of different flexibilities on the force characteristics of oscillation and gliding motion are obtained. The results show that the influence of flexibility on the lift and drag force is different. Optimal motion performance can be achieved within a certain range of flexibility. The ground effect features of the flexible bionic wing with different locomotion modes are acquired.

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Numerical Analysis of Joukowski (T = 12%) Airfoil by k-ε Turbulence Model at High Reynolds Number

Jain

Sheikh

Singh

et al. 2020

Intelligent Computing Applications for Sustainable Real-World Systems

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Ground effects on the stability of separated flow around a NACA 4415 airfoil at low Reynolds numbers

Cited by 26 publications

References 44 publications

Stability of Low-Reynolds-Number Separated Flow Around an Airfoil Near a Wavy Ground

Stability of Low-Reynolds-Number Separated Flow Around an Airfoil Near a Wavy Ground

Analysis of fluid and solid interaction of the flexible bionic wing in ground effect

Numerical Analysis of Joukowski (T = 12%) Airfoil by k-ε Turbulence Model at High Reynolds Number

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