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

Ma, Bao-Feng; Yu, Hui; Liu, Tongxin

doi:10.1016/j.cja.2014.06.011

Cited by 16 publications

(13 citation statements)

References 20 publications

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“…Strouhal numbers (St) of the sectional side-force at X/D = 2.5 were calculated and compared with published experimental data. 18 It can be seen that the St begins to agree with the experimental value as grid density excesses 4 × 10 6 . In the simulation, the 8, 234, 790 grid cells were used for formal computation.…”

supporting

confidence: 58%

“…The results showed that the dominant frequencies of side-forces were far less than Kármán vortex shedding. Nevertheless, the experiment by Ma et al 18 cannot conclusively determine the sources of fluctuations of wall pressures and side-forces. Although Particle Image Velocimetry (PIV) was also used to reveal flow evolution, PIV is not time-resolved, so unable to identify frequencies of vortex fluctuations and to connect the fluctuations of side-forces to unsteadiness of vortices.…”

mentioning

confidence: 99%

“…They speculated that the low-frequency component comes from fluctuation of fore-body vortices. Ma et al 18 studied specially the low-frequency phenomenon over the fore-body through distributing a pressure-measurement ring around one section of the fore-body, and the pressure measured was integrated to obtain the sectional side-forces. The results showed that the dominant frequencies of side-forces were far less than Kármán vortex shedding.…”

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confidence: 99%

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Low-frequency vortex oscillation around slender bodies at high angles-of-attack

Liu

2014

Physics of Fluids

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Low-frequency unsteadiness of vortices over an ogive-cylinder body was studied using numerical simulation and Dynamic Mode Decomposition (DMD). The results revealed that the vortices over the fore-body of the slender body can exhibit vortex oscillation with a non-dimensional frequency of 0.054 at 70° angle-of-attack, but the flow pattern over the aft-body downstream is Kármán vortex shedding. The vortex oscillation induces larger sectional side-forces on the body than vortex shedding. The DMD analysis for the sectional flow fields at various sections shows that the most energetic mode corresponds to the vortex oscillation at the fore-body and the vortex shedding at the aft-body except the mode for a mean flow, and the associated frequencies are identical to the ones of the sectional side-forces obtained by Fourier transformation.

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confidence: 58%

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confidence: 99%

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Low-frequency vortex oscillation around slender bodies at high angles-of-attack

Liu

2014

Physics of Fluids

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“…Besides the vortex shedding, however, other unsteady flow patterns also exist 15 . Degani et al 16 17 and numerical simulations 18 indicated that the forebody vortex pair is not stationary beyond 65 o AOA, but oscillates around a time-averaged asymmetric orientation with much lower frequencies than vortex shedding. Therefore, the leeward vortices around sharp-nosed slender bodies are essentially steady at most of the AOAs, including steady symmetric and asymmetric vortices, while large-scaled vortex motions exist only at sufficiently high AOAs (more than 65 o typically ).…”

Section: Introductionmentioning

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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“…However, theses techniques were not sufficiently effective. An extensive number of experimental studies were carried out in which the asymmetry was observed and studied [2,3,10,1,7,5,8,9,4,11] . However, to the authors' knowledge, all numerical investigations of asymmetric flow around slender bodies have introduced some form of perturbations into the flow field to induce asymmetry.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Flow Around a Slender Body at High Angles of Attack

AlQadi¹

2019

JKAU Earth Sci

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A numerical investigation of flow around a slender body at high angles of attack is presented. Large eddy simulation of the flow around an ogive-cylinder body at high angles of attack is carried out. Asymmetric vortex flow was observed at angles of attack of α = 55◦ and 65◦ . The results showed that the phenomenon is present in the absence of artificial geometrical or flow perturbation. Contrary to the accepted notion that flow asymmetry is due to a convective instability, the development of vortex asymmetry in the absence of perturbations indicates the existence of absolute instability. An investigation of the unsteady flow field was carried out using dynamic mode decomposition. The analysis identified two distinct unsteady modes; high-frequency mode and low-frequency mode. At angle of attack 45◦ the high-frequency mode is dominant in the frontal part of the body and the low-frequency mode is dominant at the rear part. At α = 55◦ , the highfrequency mode is dominant downstream of vortex breakdown. At α = 65◦ , the spectrum shows a wide range of modes. Reconstruction of the dynamical modes shows that the low-frequency mode is associated with the unsteady wake and the high-frequency mode is associated with unsteady shear layer.

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

Cited by 16 publications

References 20 publications

Low-frequency vortex oscillation around slender bodies at high angles-of-attack

Low-frequency vortex oscillation around slender bodies at high angles-of-attack

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

Investigation of Flow Around a Slender Body at High Angles of Attack

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