Unsteady Trailing Vortex Evolution Behind a Wing In Ground Effect

Han, Cheolheui; Cho, Jin Soo

doi:10.2514/1.6477

Cited by 44 publications

(9 citation statements)

References 16 publications

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“…At close ground proximity, the flow starts to interact with the ground, causing stagnation of the flow below the wing surface and as a result pressure increase (ram-pressure). At the same time, tip vortices are pushed out and reduce in size and strength with the descent into ground-effect (Han and Cho, 2005), resulting ultimately in superior aerodynamic efficiency in comparison to free-flight conditions. However, ground-effect induced stagnation of the flow below the wing results into an upwards diverted flow, causing earlier leading-edge flow separation on the upper side of the wing and therefore earlier wing stall, limiting the range of efficient angles-of-attack in GE (Rozhdestvensky, 2006).…”

mentioning

confidence: 99%

On the fluid-structure interaction of flexible membrane wings for MAVs in and out of ground-effect

Bleischwitz

Kat

Ganapathisubramani

2017

Journal of Fluids and Structures

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Wind tunnel experiments are conducted at a Reynolds number of Re = 56,000, measuring rigid flat-plates and flexible membrane wings from free-flight into ground-effect conditions. Load cell measurements, digital image correlation and particle image velocimetry are applied in high-speed to resolve time-synchronised lift, drag and pitch oscillations simultaneously with membrane and flow dynamics. Proper orthogonal decomposition is applied on flow oscillations to determine their spatiotemporal evolution. Loads, membrane motions and flow dynamics are correlated to each other to investigate their underlying coupling physics. A membrane wing's ability of static cambering and dynamic membrane oscillations are found to be beneficial when the wing is in ground-effect, where the descent in height forces premature leading-edge vortex-shedding and drag increase. The dynamic motions of membrane wings help to exploit vortex-shedding dynamics from the leading-edge that ensures time-averaged reattached flow over the wing upper surface, resulting in further lift enhancement. Membrane wings show lag-free fluid-membrane coupling at peak-lift conditions. In post-stall conditions, the membrane is found to lag the flow dynamics, signalling the end of direct fluid-structure coupling.

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mentioning

confidence: 99%

On the fluid-structure interaction of flexible membrane wings for MAVs in and out of ground-effect

Bleischwitz

Kat

Ganapathisubramani

2017

Journal of Fluids and Structures

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“…Performance improvements result from a stagnation of the flow below the wings surface, causing a static pressure increase on the lower side of the wing (Vogt and Barber, 2012). As a result, more flow is not only diverted over the upper wing surface but also pushed out along the span direction, extending virtually the aspect-ratio of wings in ground-effect (Han and Cho, 2005). Consequently, the induced drag component can be reduced and leads ultimately to gains in aerodynamic efficiency of wings in ground-effect conditions (Ahmed and Sharma, 2005;Ahmed et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Near-wake characteristics of rigid and membrane wings in ground effect

Bleischwitz

Kat

Ganapathisubramani

2018

Journal of Fluids and Structures

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Wind tunnel measurements are conducted at a Reynolds numbers of Re = 56,000 to examine the characteristics of near-wake vortices of rigid flat-plates and membrane wings from free-flight into ground-effect conditions. Synchronised high-speed load cell measurements, digital image correlation and particle image velocimetry are performed to resolve lift, drag and pitch oscillations simultaneously with membrane deformation and flow dynamics. Flow measurements are acquired in a crossflow-plane, one chord downstream of the trailing-edge, allowing the examination of time evolution of the wake and its relationship to the forces and membrane deformation. Membrane wings are found to delay ground-effect or high angles-of-attack induced tip-vortex break-down and result in larger tip-vortex push-out (beyond the wing span) compared to rigid flat-plate wings. The leading-edge vortex appears to shed with streamwise vorticity close to the root of the wing and this frequency of this shedding is found to match with the dominant frequency observed in membrane fluctuations. In specific resonance conditions, membrane and flow fluctuations are found to correlate well to the fluctuations in loads and moments.

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“…Morky [11] developed a 2-dimensional algorithm (based on the constant vortex sheet method) for modeling the evolution and propagation of aircraft trailing vortices in a sheared environment near the ground. Han and Cho [12] investigated the unsteady evolution of trailing vortex sheets behind a wing in ground effect using a discrete vortex method.…”

Section: Introductionmentioning

confidence: 99%

“…Han and Cho [12] assumed that the wings in close formation flight near the ground have the elliptic load distributions. Windall and Barrow [13] showed, based on a linear approach, that semi-elliptic wing planform with parabolic wing loading is optimal for a wing in ground effect for all aspect ratios.…”

Section: Introductionmentioning

confidence: 99%

Study on the Wake Shape behind a Wing in Ground Effect Using an Unsteady Discrete Vortex Panel Method

Han

Kinnas²

2013

OJFD

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The unsteady evolution of trailing vortex sheets behind a wing in ground effect is simulated using an unsteady discrete vortex panel method. The ground effect is included by image method. The present method is validated by comparing the simulated wake roll-up shapes to published numerical results. When a wing is flying in a very close proximity to the ground, the optimal wing loading is parabolic rather than elliptic. Thus, a theoretical model of wing load distributions is suggested, and unsteady vortex evolutions behind lifting lines with both elliptic and parabolic load distributions are simulated for several ground heights. For a lifting line with elliptic and parabolic loading, the ground has the effect of moving the wingtip vortices laterally outward and suppressing the development of the vortex. When the wing is in a very close proximity to the ground, the types of wing load distributions does not affect much on the overall wake shapes, but parabolic load distributions make the wingtip vortices move more laterally outward than the elliptic load distributions.

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Unsteady Trailing Vortex Evolution Behind a Wing In Ground Effect

Cited by 44 publications

References 16 publications

On the fluid-structure interaction of flexible membrane wings for MAVs in and out of ground-effect

On the fluid-structure interaction of flexible membrane wings for MAVs in and out of ground-effect

Near-wake characteristics of rigid and membrane wings in ground effect

Study on the Wake Shape behind a Wing in Ground Effect Using an Unsteady Discrete Vortex Panel Method

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