Effects of Forced Asymmetric Transition on Vortex Asymmetry Around Slender Bodies

Ma, Bao-Feng; Xueying, Deng; Chen, Ying

doi:10.2514/1.29712

Cited by 16 publications

(7 citation statements)

References 22 publications

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“…The present results of time-averaged side forces are comparable to the previous research. 5,6,22 Besides the time-averaged results, Fig. 3 also presents the RMS of instantaneous side forces for two locations of the tip perturbation, and the fluctuation magnitudes for the two cases are similar.…”

Section: Resultsmentioning

confidence: 87%

“…The method of identifying separation types in terms of pressure distributions is based on previous research. 22,23 The pressure suction peaks are induced by the lower vortex in an asymmetric vortex pair adjacent to the body surface. At a = 70°, the third vortex in a multivortex structure of a slender body has moved forward beyond the x/D = 2.5 section, so the pressure distribution there has been dominated by the lower vortex of the nose vortex pair and the third vortex under the original higher vortex.…”

Section: Pressure Distributions and Piv Resultsmentioning

confidence: 99%

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Low-frequency unsteadiness of vortex wakes over slender bodies at high angle of attack

Liu

2014

Chinese Journal of Aeronautics

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A type of flow unsteadiness with low frequencies and large amplitude was investigated experimentally for vortex wakes around an ogive-tangent cylinder. The experiments were carried out at angles of attack of 60-80°and subcritical Reynolds numbers of 0.6-1.8 · 10 5 . The reduced frequencies of the unsteadiness are between 0.038 and 0.072, much less than the frequency of Karman vortex shedding. The unsteady flow induces large fluctuations of sectional side forces. The results of pressure measurements and particle image velocimetry indicate that the flow unsteadiness comes from periodic oscillation of the vortex wakes over the slender body. The time-averaged vortex patterns over the slender body are asymmetric, whose orientation is dependent on azimuthal locations of tip perturbations. Therefore, the vortex oscillation is a type of unsteady oscillation around a time-averaged asymmetric vortex structure. ª 2014 Production and hosting by Elsevier Ltd. on behalf of CSAA & BUAA.

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Section: Resultsmentioning

confidence: 87%

Section: Pressure Distributions and Piv Resultsmentioning

confidence: 99%

Low-frequency unsteadiness of vortex wakes over slender bodies at high angle of attack

Liu

2014

Chinese Journal of Aeronautics

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“…The Reynolds number in the simulation is 2.2×10 4 based on the cylinder diameter, so the flow is located at the range of subcritical Re regime where boundary layers exhibit laminar separation 3,8 .…”

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confidence: 99%

Vortex Oscillations Around a Hemisphere-Cylinder Body with a High Fineness Ratio

Yin

2018

AIAA Journal

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In our previous studies (Ma and Liu, Phy Fluids, 2014; Ma, Huang, and Liu, Chin J Aeronaut, 2014), the unsteady vortex flows around a pointed-ogive slender body were studied by means of numerical simulations and experiments, and low-frequency vortex oscillations were found over the forebody as angles of attack (AOAs) more than 65 o . In this investigation, the vortex unsteadiness around a hemisphere-cylinder body with a fineness ratio (the ratio of length L to diameter D of a body, L/D) of 24 at AOAs of 10 o to 80 o was studied using Large Eddy Simulation (LES) and Dynamic Mode Decomposition (DMD). The Reynolds number (Re) based on the cylinder diameter of the body is 22000. The results show that the vortex oscillations still exist over the hemisphere-nose slender body, but the vortex behaviors are much different from the ones over the pointed-nose bodies. The vortex oscillation exists over the forebody at the whole range of AOAs, and occurs even at the AOA of 10 o . The oscillation is characterized by alternate oscillations of a forebody leeward vortex pair up and down and in-phase swings from side to side. The vortex shedding can be found at the afterbody as AOAs more than 20 o , and the shedding region moves forwards gradually with AOAs increasing, and accordingly the region of vortex oscillations contracts and eventually only exists near the nose as AOAs sufficiently high. The vortex oscillation and shedding all induce fluctuating side forces along the body, but the ones from vortex oscillations are larger. The frequencies of vortex oscillations are similar to the ones of vortex shedding at the AOAs of 10 o -40 o with St=0.085-0.12, in which the flow fields over the afterbody are dominated by vortex shedding and forebody-vortex wakes together; while at AOAs of 50 o -80 o , the frequencies along the body are apparently divided into two regimes in which the vortex oscillations over the forebody have the frequencies of 0.053-0.064, and the vortex shedding over the afterbody has the frequencies of 0.16-0.2. Additionally, as AOAs beyond 40 o , the frequencies are basically proportional to the sine function of AOAs. The simulated frequencies agree well with previous experimental results obtained by hotwire velocity measurements (Hoang et al., Exp Fluids, 1999). The oscillatory global modes based on the sectional flow snapshots were obtained through DMD analysis. The results show that except the mean flows, the most energetic modes correspond to the vortex oscillation at the forebody and to the vortex shedding at the afterbody respectively, and the frequencies from DMD are identical to the ones of the side forces obtained by fast Fourier transform. In addition, both the time-averaged side forces and vorticity fields show that the mean flow fields for the vortex oscillations are symmetric, and no apparent asymmetry exists. Therefore, the vortex pair over the forebody oscillates around a symmetric mean flow field.

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“…The section was 1.5 m wide, 1.5 m high, and 2.5 m long, with turbulence level of less than 0.1% and maximum speed of 60 m∕s. The introduction of the wind tunnel also can be found in [16,17]. Figure 1a showed the schematic diagram of the experimental layout.…”

Section: Methodsmentioning

confidence: 99%

Wing Rock Induced by a Hemisphere–Cylinder Forebody

Wei

2014

Journal of Aircraft

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The wing rock induced by a hemisphere-cylinder forebody was investigated experimentally using an isolated delta wing and wing body. For the delta wing with sweep angle of 30 deg, no apparent limit-cycle wing rock occurs at angles of attack of 0-90 deg. The mean roll angles exhibit nonzero values at angles of attack of less than 15 deg and become zero at angles of attack of more than 15 deg. For the wing body with a hemisphere-cylinder forebody, apparent wing rock exists at angles of attack of 0-90 deg; the wing rock is induced by the forebody. The phase diagrams showed that the wing rock motion is a typical limit-cycle oscillation at lower and moderate angles of attack. With increasing angles of attack, however, stochastic components in wing rock motion are increased gradually, and the motion types start to deviate from a limit-cycle oscillation. The phase-locked particle-image-velocimetry measurements for the wing body revealed that the vortex pair over the forebody exhibits apparent dynamic hysteresis in position and strength during wing rock, and the dynamic hysteresis of forebody vortices further influence flowfields over the wing, resulting in asymmetric distributions of wing flow, which provides the driving moments sustaining the wing rock.Nomenclature D = diameter of cylindrical body, mm L = span length of wing, mm I = I∕ρL 5 , nondimensional moment of inertia about X axis p = _ ϕL∕U ∞ , nondimensional roll rate Re D = U ∞ D∕ν, Reynolds number based on body diameter U ∞ = freestream velocity, m∕s X = streamwise coordinate, mm α = angle of attack, deg ν = kinematic viscosity coefficient of air, m 2 ∕s ρ = density of air, kg∕m 3 ϕ = roll angle, deg ω = ωL∕U ∞ , nondimensional vorticity

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Effects of Forced Asymmetric Transition on Vortex Asymmetry Around Slender Bodies

Cited by 16 publications

References 22 publications

Low-frequency unsteadiness of vortex wakes over slender bodies at high angle of attack

Low-frequency unsteadiness of vortex wakes over slender bodies at high angle of attack

Vortex Oscillations Around a Hemisphere-Cylinder Body with a High Fineness Ratio

Wing Rock Induced by a Hemisphere–Cylinder Forebody

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