Unsteady vortex structure over delta-wing subject to transient along-core blowing

Kuo, Cheng‐Hsiung; Lu, Ni-Yu

doi:10.2514/3.14019

Cited by 3 publications

(4 citation statements)

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“…Although complete understanding of the flow phenomenon still eludes researchers, the need to manage vortex breakdown over a delta wing at high angles of attack has, over the years, led many to propose a wide range of flow control techniques (see Mitchell and Délery [10]) and devices such as leading-edge flaps [11][12][13][14], apex fences [15], or even blowing and suction in the tangential direction along a rounded leading edge [16,17], and suction near the separation point [18][19][20]. It is generally agreed that trailing-edge blowing [21][22][23][24][25][26] or suction [27] techniques delay vortex breakdown by altering the downstream pressure gradient, and the along-core blowing technique [28][29][30][31][32] delays vortex breakdown by increasing the axial velocity (i.e., a reduction in the swirl number). Although there are many other blowing/suction techniques, including different blowing/suction locations and orientations, they all function more or less the same way.…”

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confidence: 99%

Control of Vortex Breakdown over a Delta Wing Using Forebody Spanwise Slot Blowing

2007

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In this paper we study the effectiveness of forebody slot blowing to control vortex breakdown over a generic delta wing-body configuration. The motivation is to exploit the benefits of both slot blowing and canards to control vortex breakdown over a delta wing. Parameters investigated include slot length, slot width, single and double-sided blowing, and the Reynolds number. Time-averaged flow images show that Reynolds number has little effect on vortex breakdown location, at least for the range of conditions studied here, and a single-sided blowing has favorable effects on the blowing side and unfavorable effects on the nonblowing side. It is postulated that when fluid is discharged from the slot at the forebody in the spanwise direction, it produces a vortex sheet that interacts with the freestream and is rolled up to form a trailing vortex further downstream. The rolled-up vortex sheet produces a downwash effect on the blowing side and a sideslip effect on the opposite side. The downwash modifies the flowfield around the leading edge of the wing, causing a delay in vortex breakdown. To compensate for the unfavorable effects of blowing on the opposite side, a much higher blowing momentum (more than two times the single-sided slot case) is needed to delay vortex breakdown on both sides of the wing when double-sided blowing is employed. Our results also show that for a given Reynolds number and angle of attack, increasing the blowing momentum leads to a substantial delay in the vortex breakdown position. In addition, for the same blowing momentum coefficient, varying the slot width has little effect on the breakdown location, whereas increasing the slot length has favorable effect, particularly at lower angles of attack. Nomenclature A j = slot area AOA = angle of attack c = root chord C m = blowing momentum coefficient, Q 2 =A j qS f = oscillating frequency of the vortex breakdown location Q = volume flow rate of blowing Re = Reynolds number, Uc=v S = area of the delta wing SL = slot length U = freestream velocity V j = average slot exit velocity Vr = velocity ratio, V j =U W = slot width X b = vortex breakdown position from the apex of the wing X bmean = mean vortex breakdown position v = kinematic viscosity of water

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confidence: 99%

Control of Vortex Breakdown over a Delta Wing Using Forebody Spanwise Slot Blowing

2007

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“…It is generally believed that trailing-edge blowing [23][24][25][26][27][28] or suction [29] techniques delay vortex breakdown by decreasing the downstream pressure gradient, and along-the-core blowing technique [30][31][32][33][34] delays vortex breakdown by increasing the axial velocity (i.e., a reduction in the swirl number). Dixon [35] believed that SWB on the wing provides sweeplike effects as the SWB jets are entrained in the leading-edge vortices.…”

Section: Nomenclaturementioning

confidence: 99%

“…These include mechanical devices such as leading-edge flaps [9][10][11][12], apex fences [13], canards, strakes, leading-edge extensions (LEXs), or double-delta wing [14][15][16][17][18][19][20][21][22] and pneumatic techniques such as trailing-edge blowing [23][24][25][26][27][28] or suction [29], along-the-core blowing technique [30][31][32][33][34], spanwise blowing (SWB) [35][36][37], and some other blowing/suction techniques [38] with different blowing/suction locations and orientations.…”

Section: Nomenclaturementioning

confidence: 99%

Forebody Slot Blowing on Vortex Breakdown and Load Over a Delta Wing

2008

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shows that a forebody slot blowing technique significantly delays vortex breakdown over a delta wing. Blowing only on one side while delaying vortex breakdown has an opposite effect on the nonblowing side. Although the authors provided a plausible explanation for the observed behavior, no concrete evidence was given. In this paper, we address this issue and further evaluate the effects of symmetric and differential blowing on the aerodynamic loads. Flow visualization and force measurement were carried out in a water tunnel at a Reynolds number of 8:5 10 4 . Our study shows that the differing effect of differential blowing can be traced to a combination of forebody slot blowing itself and the interaction of the vortices from both sides resulting in a side-slip-like effect. Moreover, symmetrical forebody slot blowing, apart from producing a significant delay in the formation of vortex breakdown, increases the lift by more than 5%. Differential blowing can be used to manipulate the vortex breakdown position and change the roll moment of the wing, which suggests that the method can be a potential means for roll control. Nomenclature= blowing momentum coefficient for port side slot C S = blowing momentum coefficient for starboard side slot c = root chord Q = volume flow rate of blowing q = dynamic pressure of freestream Re = Reynolds number, Uc=v S = area of delta wing U = freestream velocity V j = average slot exit velocity X b = vortex breakdown position from the apex of the wing X bmean = mean vortex breakdown position X bmean P = mean port side vortex breakdown position X bmean S = mean starboard side vortex breakdown position = kinematic viscosity of water = density of blowing fluid

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“…Suction near the separation point was another technique that was implemented to control the location and direction of the primary vortices [39]. Near core blowing was investigated by Kuo an Lu [40] and Guillot et al [41], and Liu et al [42] used closed-loop active flow controller to derive the efficient injection cycles of the controlling jets along the vortex core.…”

Section: Vortex Breakdownmentioning

confidence: 99%

Effect of thickness-to-chord ratio on aerodynamics of non-slender delta wing

Ghazijahani

Yavuz

2019

Aerospace Science and Technology

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, 84 pages Flow characterization over delta wings have gained attention in recent decades due to their prevailing usage in designs of unmanned air vehicles (UAVs). In literature, only a few studies have reported wing thickness effect on both the aerodynamic performance and detailed flow structure over delta wings. In the present investigation, the effect of thickness-to-chord (/) ratio on aerodynamics of a non-slender delta wing with 45 degree sweep angle is characterized in a low-speed wind tunnel using laser illuminated smoke visualization, surface pressure measurements, particle image velocimetry, and force measurements. The delta wings with / ratios varying from 2 % to 15 % are tested at broad ranges of angle of attack and Reynolds number. The results indicate that the effect of / ratio on flow structure is quite substantial. Considering the low angles of attack where the wings experience leading edge vortex structure, the strength of the vortex structure increases as the / ratio increases. However, low / ratio wings have pronounced surface separations at higher angle of attack compared to the high / ratio wings. These results are well supported by the force measurements such that high / ratio wings induce higher lift coefficients, CL, at vi low angles of attack, whereas maximum CL values are higher and appear at higher angle of attack for low / ratio wings. This indicates that low / ratio wings are more resistive to the stall condition. Considering the lift-to-drag ratio, CL/CD, increase in / ratio induces remarkable drop in CL/CD values.

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Unsteady vortex structure over delta-wing subject to transient along-core blowing

Cited by 3 publications

References 0 publications

Control of Vortex Breakdown over a Delta Wing Using Forebody Spanwise Slot Blowing

Control of Vortex Breakdown over a Delta Wing Using Forebody Spanwise Slot Blowing

Forebody Slot Blowing on Vortex Breakdown and Load Over a Delta Wing

Effect of thickness-to-chord ratio on aerodynamics of non-slender delta wing

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