Boundary-layer flows from fixed to moving surfaces including gap effects

Tennant, J. S.; Johnson, W. S.; Keaton, D.D.

doi:10.2514/3.48161

Cited by 21 publications

(4 citation statements)

References 4 publications

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“…For zero angle of attack, the lift coefficient of 1.2 was attained with U c /U = 3. Also of interest is their study concerning the boundary-layer growth on moving surfaces accounting for gap effects [25,26].…”

Section: Noeuverability Extensive Force Measurements and Flow Visualmentioning

confidence: 99%

Fluid dynamics of airfoils with moving surface boundary layer control

Mokhtarian

Modi

1986

Astrodynamics Conference

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In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.Department of Mecl'itt.n.iCfrt EmflirveeriVyg ABSTRACTThe concept of moving surface boundary-layer control, as applied to the Joukowsky and NACA airfoils, is investigated through a planned experimental program complemented by theoretical and flow visualization studies. The moving surface was provided by one or two rotating cylinders located at the leading edge, the trailing edge, or the top surface of the airfoil. Three carefully designed two-dimensional models, which provided a wide range of single and twin cylinder configurations, were tested at a subcritical Reynolds number (Re = 4.62 x 10 4 or Re -2.31 x 10 5 ) in a laminar-flow tunnel over a range of angles of attack and cylinder rotational speeds. The test results suggest that the concept is indeed quite promising and can provide a substantial increase in lift and a delay in stall.The leading-edge rotating cylinder effectively extends the lift curve without substantially affecting its slope. When used in conjunction with a second cylinder on the upper surface, further improvements in the maximum lift and stall angle are possible. The maximum coefficient of lift realized was around 2.22, approximately 2.6 times that of the base airfoil. The maximum delay in stall was to around 45°. In general, the performance improves with an increase in the ratio of cylinder surface speed (U c ) to the free stream speed (U). However, the additional benefit derived progressively diminishes with an increase in U c /U and becomes virtually negligible for U c /U > 5.There appears to be an optimum location for the leading-edge-cylinder. Tests with the cylinder at the upper side of the leading edge gave quite promising results.Although the Cx jmai obtained was a little lower than the two-cylinder configuration (1.95 against 2.22), it offers a major advantage in terms of mechanical simplicity.Performance of the leading-edge-cylinder also depends on its geometry. A scooped configuration appears to improve performance at lower values of U c /U (U c /U < 1).However, at higher rates of rotation the free stream is insensitive to the cylinder geometry and there is no particular advantage in using the scooped geometry.A rotating trailing-edge-cylinder affects the airfoil characteristics in a fundamentally different manner. In contrast to the leading-edge-cylinder, it acts as a flap by shifting the CL vs. a plots to the left thus increasing the lift coefficient at smaller angles of attack before stall. For example, at a = 4°, it changed the lift coefficient from 0.35 to 1.5, an increase ...

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Section: Noeuverability Extensive Force Measurements and Flow Visualmentioning

confidence: 99%

Fluid dynamics of airfoils with moving surface boundary layer control

Mokhtarian

Modi

1986

Astrodynamics Conference

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“…Mokhtarian et al numerically analyzed the effects of leading-edge rotating cylinders on symmetrical and asymmetrical airfoils [24,25], finding that at rotation speed ratios of 1 and 2, both types of airfoils experienced increased lift and stall angles. Tennant et al recorded changes in the lift coefficient [26] and boundary layer [27] for airfoils with trailing-edge rotating cylinders at rotation speed ratios of 3 and 4 and summarized the current applications of the Magnus effect [28], finding that the trends in lift curve changes at high and low rotation speed ratios were opposite. Al-Garni conducted experimental studies on an NACA0024 airfoil with leading-edge rotating cylinders and flaps [20], finding that resistance increased with increasing rotation speed ratio.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Energy Harvesting Efficiency of Flapping Wings with Leading-Edge Magnus Effect Cylinder

Zhang,

Zhu,

Chen

2024

Biomimetics

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According to the Magnus principle, a rotating cylinder experiences a lateral force perpendicular to the incoming flow direction. This phenomenon can be harnessed to boost the lift of an airfoil by positioning a rotating cylinder at the leading edge. In this study, we simulate flapping-wing motion using the sliding mesh technique in a heaving coordinate system to investigate the energy harvesting capabilities of Magnus effect flapping wings (MEFWs) featuring a leading-edge rotating cylinder. Through analysis of the flow field vortex structure and pressure distribution, we explore how control parameters such as gap width, rotational speed ratio, and phase difference of the leading-edge rotating cylinder impact the energy harvesting characteristics of the flapping wing. The results demonstrate that MEFWs effectively mitigate the formation of leading-edge vortices during wing motion. Consequently, this enhances both lift generation and energy harvesting capability. MEFWs with smaller gap widths are less prone to induce the detachment of leading-edge vortices during motion, ensuring a higher peak lift force and an increase in the energy harvesting efficiency. Moreover, higher rotational speed ratios and phase differences, synchronized with wing motion, can prevent leading-edge vortex generation during wing motion. All three control parameters contribute to enhancing the energy harvesting capability of MEFWs within a certain range. At the examined Reynolds number, the optimal parameter values are determined to be a∗ = 0.0005, R = 3, and ϕ0 = 0°.

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“…Tennant et al conducted a research incorporating a trailing edge rotating cylinder and documented potential outcome of C L = 1.2 for higher velocity ratio [13]. They also explored the growth of the boundary layer on the moving surface [14,15]. Mokhtarian studied the effect of MSBC incorporating a scooped leading edge rotating cylinder and concluded that although it would outperform solid leading edge rotating cylinder at low velocity ratios [16].…”

Section: Introductionmentioning

confidence: 99%

Moving Surface Boundary Layer Control Analysis and the Influence of the Magnus Effect on an Aerofoil with a Leading-Edge Rotating Cylinder

Salam¹,

Hai²,

Ali³

et al. 2019

Preprint

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A number of experimental and numerical studies point out that incorporating a rotating cylinder can superiorly enhance the aerofoil performance, especially for higher velocity ratios. Yet, there have been less or no studies exploring the effects of lower velocity ratio at a higher Reynolds number. In the present study, we investigated the effects of Moving Surface Boundary-layer Control (MSBC) at lower velocity ratios (i.e. cylinder tangential velocity to free stream velocity) and higher Reynolds number on a symmetric aerofoil (e.g. NACA 0021) and an asymmetric aerofoil (e.g. NACA 23018). In particular, the aerodynamic performance with and without rotating cylinder at the leading edge of the NACA 0021 and NACA 23018 aerofoil was studied on the wind tunnel installed at Aerodynamics Laboratory. The aerofoil section was tested in the low subsonic wind tunnel, and the lift coefficient and the drag coefficient were studied for different angles of attack. The experiments were conducted for two Reynolds numbers: 200000 and 250000 corresponding to two free stream velocities: 20 m/s and 25 m/s, respectively, for six different angle of attacks (-5°, 0°, 5°, 10°, 15° and 20°). This study demonstrates that the incorporation of a leading edge rotating cylinder results in an increase of lift coefficient at lower angle of attacks (maximum around 33%) and delay in stall angle (from 10° to 15°) relative to the aerofoil without rotating cylinder.

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Boundary-layer flows from fixed to moving surfaces including gap effects

Cited by 21 publications

References 4 publications

Fluid dynamics of airfoils with moving surface boundary layer control

Fluid dynamics of airfoils with moving surface boundary layer control

Enhancing Energy Harvesting Efficiency of Flapping Wings with Leading-Edge Magnus Effect Cylinder

Moving Surface Boundary Layer Control Analysis and the Influence of the Magnus Effect on an Aerofoil with a Leading-Edge Rotating Cylinder

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