Variation of Leading-Edge Suction at Stall for Steady and Unsteady Airfoil Motions

Narsipur, Shreyas; Hosangadi, Pranav; Gopalarathnam, Ashok; Edwards, Jack R.

doi:10.2514/6.2016-1354

Cited by 9 publications

(25 citation statements)

References 35 publications

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“…In both fish species, as in airfoils with an angle of attack to the flow (Fig. 1A,C) (11,12,(14)(15)(16), the region of positive pressure is not directly on the tip of the snout (Fig. 4; Movies S3, S4).…”

Section: The Anterior Body Produces Thrust Due To Airfoil-like Mechanicsmentioning

confidence: 97%

“…When the airfoil is angled, the stagnation point and region of positive pressure is not directly on the tip of the airfoil (Fig. 1A,C) (15,16). When the positive pressure deflects to one side, negative pressure moves forward to act more anteriorly on the opposite side (compare Fig.…”

Section: Introductionmentioning

confidence: 98%

“…When the positive pressure deflects to one side, negative pressure moves forward to act more anteriorly on the opposite side (compare Fig. 1B,C) (15,16). This area of negative pressure, positioned alongside forward-facing surfaces near the airfoil's leading edge, acts as local forces with small thrust components in a mechanism called leading-edge suction (Fig.…”

Section: Introductionmentioning

confidence: 98%

“…1B) (4,11,14). Airfoils also produce thrust on their anterior regions through leading-edge suction when they are at an angle to the flow (12,15,16). When the airfoil is angled, the stagnation point and region of positive pressure is not directly on the tip of the airfoil (Fig.…”

Section: Introductionmentioning

confidence: 99%

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The fish body functions as an airfoil: surface pressures generate thrust during carangiform locomotion

Lucas

Lauder

Tytell

2020

Preprint

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The anterior body of many fishes is shaped like an airfoil turned on its side. With an oscillating angle to the swimming direction, such an airfoil experiences negative pressure due to both its shape and pitching movements. This negative pressure acts as thrust forces on the anterior body. Here, we apply a high-resolution, pressure-based approach to describe how two fishes, bluegill sunfish (Lepomis macrochirus Rafinesque) and brook trout (Salvelinus fontinalis Mitchill), swimming in the carangiform mode, the most common fish swimming mode, generate thrust on their anterior bodies using leading-edge suction mechanics, much like an airfoil. These mechanics contrast with those previously reported in lampreys -anguilliform swimmers -which produce thrust with negative pressure but do so through undulatory mechanics. The thrust produced on the anterior body of these carangiform swimmers through negative pressure comprises 28% of the total thrust produced over the body and caudal fin, substantially decreasing the net drag on the anterior body. On the posterior region, subtle differences in body shape and kinematics allow trout to produce more thrust than bluegill, suggesting that they may swim more effectively. Despite the large phylogenetic distance between these species, and differences near the tail, the pressure profiles around the anterior body are similar. We suggest that such airfoillike mechanics are highly efficient, because they require very little movement and therefore relatively little active muscular energy, and may be used by a wide range of fishes since many species have appropriately-shaped bodies. Significance StatementMany fishes have bodies shaped like a low-drag airfoil, with a rounded leading edge and a smoothly tapered trailing region, and move like an airfoil pitching at a small angle. This shape reduces drag but its significance for thrust production by fishes has not been investigated experimentally. By quantifying body surface pressures and forces during swimming, we find that the anterior body shape and movement allows fishes to produce thrust in the same way as an oscillating airfoil. This work helps us to understand how the streamlined body shape of fishes contributes, not only to reducing drag, but also directly to propulsion, and, by quantitatively linking form and function, leads to a more complete understanding fish evolution and ecology.

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Section: The Anterior Body Produces Thrust Due To Airfoil-like Mechanicsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The fish body functions as an airfoil: surface pressures generate thrust during carangiform locomotion

Lucas

Lauder

Tytell

2020

Preprint

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“…Research efforts at NC State directed towards unsteady aerodynamics lead to the development of a low-order method for modeling flows past airfoils undergoing arbitrary combinations of pitch, plunge and surge motions [86,87,88,89]. The primary focus was to model the formation and effects of leading-edge vortices.…”

Section: Background and Formulationmentioning

confidence: 99%

Leading-Edge Flow Sensing for Aerodynamic Parameter Estimation

Saini

Gopalarathnam

2018

AIAA Journal

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SAINI, ADITYA. Leading-Edge Flow Sensing for Aerodynamic Parameter Estimation. (Under the direction of Dr. Ashok Gopalarathnam.) The identification of inflow air data quantities such as airspeed, angle of attack, and local lift coefficient on various sections of a wing or rotor blade provides the capability for load monitoring, aerodynamic diagnostics, and control on devices ranging from air vehicles to wind turbines. Real-time measurement of aerodynamic parameters during flight provides the ability to enhance aircraft operating capabilities while preventing dangerous stall situations. This thesis presents a novel Leading-Edge Flow Sensing (LEFS) algorithm for the determination of the air-data parameters using discrete surface pressures measured at a few ports in the vicinity of the leading edge of a wing or blade section. The approach approximates the leading-edge region of the airfoil as a parabola and uses pressure distribution from the exact potential-flow solution for the parabola to fit the pressures measured from the ports. Pressures sensed at five discrete locations near the leading edge of an airfoil are given as input to the algorithm to solve the model using a simple nonlinear regression. The algorithm directly computes the inflow velocity, the stagnation-point location, section angle of attack and lift coefficient. The performance of the algorithm is assessed using computational and experimental data in the literature for airfoils under different flow conditions. The results show good correlation between the actual and predicted aerodynamic quantities within the pre-stall regime, even for a rotating blade section. Sensing the deviation of the aerodynamic behavior from the linear regime requires additional information on the location of flow separation on the airfoil surface. Bio-inspired artificial hair sensors were explored as a part of the current research for stall detection. The response of such artificial micro-structures can identify critical flow characteristics, which relate directly to the stall behavior. The response of the microfences was recorded via an optical microscope for flow over a flat plate at different freestream velocities in the NCSU subsonic wind tunnel. Experi

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A vorticity-based criterion to characterise leading edge dynamic stall onset

2022

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We propose a more conservative, physically-intuitive criterion, namely, the boundary enstrophy flux ( $BEF$ ), to characterise leading-edge-type dynamic stall onset in incompressible flows. Our results are based on wall-resolved large-eddy simulations of pitching aerofoils, with fine spatial and temporal resolution around stall onset. We observe that $|BEF|$ reaches a maximum within the stall onset regime identified. By decomposing the contribution to $BEF$ from the flow field, we find that the dominant contribution arises from the laminar leading edge region, due to the combined effect of large clockwise vorticity and favourable pressure gradient. A relatively small contribution originates from the transitional/turbulent laminar separation bubble (LSB) region, due to LSB-induced counter-clockwise vorticity and adverse pressure gradient. This results in $BEF$ being nearly independent of the integration length as long as the region very close to the leading edge is included. This characteristic of $BEF$ yields a major advantage in that the effect of partial or complete inclusion of the noisy LSB region can be filtered out, without changing the $BEF$ peak location in time significantly. Next, we analytically relate $BEF$ to the net wall shear and show that its critical value ( $=\max (|BEF|)$ ) corresponds to the instant of maximum net shear prevailing at the wall. Finally, we have also compared $BEF$ with the leading edge suction parameter ( $LESP$ ) (Ramesh et al., J. Fluid Mech., vol. 751, 2014, pp. 500–538) and find that the former reaches its maximum value between $0.3^{\circ }$ and $0.8^{\circ }$ of rotation earlier.

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Variation of Leading-Edge Suction at Stall for Steady and Unsteady Airfoil Motions

Cited by 9 publications

References 35 publications

The fish body functions as an airfoil: surface pressures generate thrust during carangiform locomotion

The fish body functions as an airfoil: surface pressures generate thrust during carangiform locomotion

Leading-Edge Flow Sensing for Aerodynamic Parameter Estimation

A vorticity-based criterion to characterise leading edge dynamic stall onset

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