Interaction of tip vortex and laminar separation bubble over wings with different aspect ratios under low Reynolds numbers

Genç, Mustafa Serdar; Özkan, Gökhan; Özden, Mustafa; ̇ş, Mehmet Sadik Ki ̇ri; ̇z, Rahime Yi ̇ldi

doi:10.1177/0954406217749270

Cited by 34 publications

(21 citation statements)

References 37 publications

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“…This implicates that stall occurs at higher angles of attack compared to a two-dimensional airfoil, because new fluid from the pressure side can enter the boundary layer on the suction side and the flow remains attached to the airfoil surface for a longer downstream distance. This phenomenon was also observed by Genç et al (2018), where for a NACA 4412 with AR = 3 the separation of the shear layer was suppressed by the formation of tip vortices, thus causing a delay of stall for angles of attack up to 40 • and Reynolds number 50,000. For higher Reynolds numbers, the finite airfoil acted as a 2D airfoil because the effect of viscous forces and leading edge vortices on the flow decreased.…”

Section: Hot-wire Measurement Resultssupporting

confidence: 59%

Aeroacoustic noise reduction by application of end plates on wall-mounted finite airfoils

et al. 2021

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One known method to reduce vortex shedding from the tip of a blade is the use of end plates or winglets. Although the aerodynamic impact of such end plates has been investigated in the past, no studies exist on the effect of such end plates on the far-field noise. The aeroacoustic noise reduction of three different end-plate geometries is experimentally investigated. The end plates are applied to the free end of a wall-mounted symmetric NACA 0012 airfoil and a cambered NACA 4412 airfoil with an aspect ratio of 2 and natural boundary layer transition. Microphone array measurements are taken in the aeroacoustic open-jet wind tunnel at BTU Cottbus-Senftenberg for chord-based Reynolds numbers between 75,000 and 225,000 and angles of attack from 0$$^\circ$$ ∘ to 30$$^\circ$$ ∘ . The obtained acoustic spectra show a broad frequency hump for the airfoil base configurations at higher angles of attack that is attributed to tip noise. Hot-wire measurements taken for one configuration show that the application of an end plate diffuses the vorticity at the tip. The aeroacoustic noise contribution of the tip can be reduced when the endplates are applied. This reduction is most effective for higher angles of attack, when the tip vortex is the dominant sound source. Graphic abstract

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Section: Hot-wire Measurement Resultssupporting

confidence: 59%

Aeroacoustic noise reduction by application of end plates on wall-mounted finite airfoils

et al. 2021

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“…Recently, scientists have concentrated upon low Reynolds number aerodynamics as a result of the progression on micro air vehicle (MAV), unmanned aerial vehicles (UAV) or wind turbines. As is known, at low Re number flow regimes, a laminar separation bubble (LSB) brings about some unfavorable effects such as diminishing lift, enhancing drag, noise and vibration (Zhang et al , 2008; Ricci and Montelpare, 2005; Genç, 2010; Koca et al , 2018; Genç et al , 2018; Demir et al , 2016; Genç et al , 2016a; Demir and Genç, 2017; Karasu et al , 2018). The fluid flow is vulnerable to separate at low Reynolds number flow conditions.…”

Section: Introductionmentioning

confidence: 99%

Experimental analysis of fluid-structure interaction in flexible wings at low Reynolds number flows

Genç

Demir

Özden

et al. 2021

AEAT

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Purpose The purpose of this exhaustive experimental study is to investigate the fluid-structure interaction in the flexible membrane wings over a range of angles of attack for various Reynolds numbers. Design/methodology/approach In this paper, an experimental study on fluid-structure interaction of flexible membrane wings was presented at Reynolds numbers of 2.5 × 104, 5 × 104 and 7.5 × 104. In the experimental studies, flow visualization, velocity and deformation measurements for flexible membrane wings were performed by the smoke-wire technique, multichannel constant temperature anemometer and digital image correlation system, respectively. All experimental results were combined and fluid-structure interaction was discussed. Findings In the flexible wings with the higher aspect ratio, higher vibration modes were noticed because the leading-edge separation was dominant at lower angles of attack. As both Reynolds number and the aspect ratio increased, the maximum membrane deformations increased and the vibrations became visible, secondary vibration modes were observed with growing the leading-edge vortices at moderate angles of attack. Moreover, in the graphs of the spectral analysis of the membrane displacement and the velocity; the dominant frequencies coincided because of the interaction of the flow over the wings and the membrane deformations. Originality/value Unlike available literature, obtained results were presented comparatively using the sketches of the smoke-wire photographs with deformation measurement or turbulence statistics from the velocity measurements. In this study, fluid-structure interaction and leading-edge vortices of membrane wings were investigated in detail with increasing both Reynolds number and the aspect ratio.

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“…There were the experiments and the simulations of the flow of airfoil at low Reynolds number. The condition of the separation bubbles (laminar flow and turbulent flow) generated by the airfoil at low Reynolds number was mainly discussed in Hu and Yang 32 as well as the shedding frequency and trajectory of the vortex in Koca et al 33 and Genc et al 34 The influence of Reynolds number on the stall characteristics of airfoil was also described. 35,36 The performance of a wind turbine is generally determined by the operating conditions 37 of the blade, and improving the flow field around the blade is key to improve its output power.…”

Section: Introductionmentioning

confidence: 99%

“…33 and Genc et al. 34 The influence of Reynolds number on the stall characteristics of airfoil was also described. 35,36…”

Section: Introductionmentioning

confidence: 99%

Investigation of leading-edge slat on aerodynamic performance of wind turbine blade

Chen

Jiang

Wang

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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In this paper, the numerical simulation was used to investigate the effects of the leading-edge slat installation angles ( β for airfoils from 0° to 40° and β1 for blades from −20° to 40°) on the aerodynamic characteristics of the airfoil and the wind turbine blade. The chord length of the leading-edge slat is 0.1c (the chord length of the clean airfoil). The horizontal and vertical distances from its center to the leading edge of the clean airfoil are 0.005c and 0.009c, respectively. The results indicated that the lift coefficient could be significantly improved by the leading-edge slat (except β = 40°) when the attack angle exceeded 10.2°. For β = 0°, the lift coefficient increased the most. The trailing vortex of the leading-edge slat played an important role at the process of flow control. It could transfer kinetic energy from the bounder layer to its out-flow region. Furthermore, the vorticities of trailing vortex generated by the leading-edge slat with different installation angles were different, promoting several effects on the airfoil at the different cases. The torque of the blade with leading-edge slat (except β1 = −20°) was improved significantly as the leading-edge slat trailing-vortices became stronger with the higher wind-speeds.

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Interaction of tip vortex and laminar separation bubble over wings with different aspect ratios under low Reynolds numbers

Cited by 34 publications

References 37 publications

Aeroacoustic noise reduction by application of end plates on wall-mounted finite airfoils

Aeroacoustic noise reduction by application of end plates on wall-mounted finite airfoils

Experimental analysis of fluid-structure interaction in flexible wings at low Reynolds number flows

Investigation of leading-edge slat on aerodynamic performance of wind turbine blade

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