Wakes of three axisymmetric bodies at zero angle of attack

Ilday, Ozlem; Acar, H.; Elbay, M. K.; Atli, Veysel

doi:10.2514/3.11741

Cited by 18 publications

(7 citation statements)

References 5 publications

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“…However, at β = 22°, the flow fully separates from the boattail shoulder and the whole boattail model is located inside the separation region. Those results are consistent with the observation of Tran et al [11] at the Reynolds number around Re D = 4:34 × 10 4 .…”

Section: Resultssupporting

confidence: 93%

“…A boattail model of 5°could reduce the drag up to 21% in supersonic condition [3]. At low-speed condition, a conical boattail model of 15°allows a reduced drag around 34% [4]. Despite the simple design, flow behavior around the boattail is very complicated and is highly affected by its geometry.…”

Section: Introductionmentioning

confidence: 99%

“…However, the near-wake structure was not investigated in their study. Ilday et al [4] who employed hot-wire devices to measure near-wake of the blunt-based body and boattail model with an angle of 15°observed a noticeable decrease in the turbulent intensity and length of recirculation behind the base. Mariotti et al [6], who investigated contoured boattail models of 26.7°and 40.4°, reported two flow types on the boattail surface, which are fully attached and separated conditions.…”

Section: Introductionmentioning

confidence: 99%

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The Effect of Boattail Angles on the Near-Wake Structure of Axisymmetric Afterbody Models at Low-Speed Condition

Tran

2020

International Journal of Aerospace Engineering

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The effect of a boattail angle on the structure of the wake of an axisymmetric model was investigated at low-speed condition. Four conical boattail models with angles of 0° (blunt-based body), 10°, 16°, and 22° were selected for this study. The Reynolds number based on the diameter of the model was around 1.97×104. Particle image velocimetry (PIV) was used to measure the velocity of the wake flow. The time-averaged flow characteristics including the length of recirculation of the afterbody, turbulent intensity, and Reynolds shear stress were analyzed and compared among those boattail models. The experimental results showed that the length of recirculation decreases with increasing boattail angle to 16°. At a boattail angle above 16°, the flow was fully separated near the shoulder and near-wake structure was highly changed. The turbulent intensity at a boattail angle of 22° showed a similar level to that in the case of the blunt-based body. Flow behavior on boattail surface should be accounted as an important parameter affecting the wake width and drag of the model. Power spectral density and proper orthogonal decomposition (POD) analyses showed that a Strouhal number of StD=0.2 dominated for the boattail model up to 16°. The fully separated flow was dominated by a Strouhal number of StD=0.03−0.06, which was firstly presented in this study.

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Section: Resultssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Effect of Boattail Angles on the Near-Wake Structure of Axisymmetric Afterbody Models at Low-Speed Condition

Tran

2020

International Journal of Aerospace Engineering

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“…There were no conclusions about when the flow achieved self-similar behavior, and in fact it was not obvious that the turbulence intensities ever did. During the last decade, researchers have primarily focused on the early development of the wake behind differently shaped axisymmetric bluff bodies; among them: İlday et al, 8 Ostowari and Page, 9 Portiero and Perez-Villar, 10 and Sirviente and Patel. 11 All concluded that the wake became similar in mean velocity but the turbulence intensity profiles did not collapse.…”

Section: Historical Reviewmentioning

confidence: 99%

Equilibrium similarity, effects of initial conditions and local Reynolds number on the axisymmetric wake

2003

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Equilibrium similarity considerations are applied to the axisymmetric turbulent wake, without the arbitrary assumptions of earlier theoretical studies. Two solutions for the turbulent flow are found: one for infinite local Reynolds number which grows spatially as x1/3; and another for small local Reynolds number which grows as x1/2. Both solutions can be dependent on the upstream conditions. Also, the local Reynolds number diminishes with increasing downstream distance, so that even when the initial Reynolds number is large, the flow evolves downstream from one state to the other. Most of the available experimental data are at too low an initial Reynolds number and/or are measured too near the wake generator to provide evidence for the x1/3 solution. New results, however, from a laboratory experiment on a disk wake and direct numerical simulations (DNS) are in excellent agreement with this solution, once the flow has had large enough downstream distance to evolve. Beyond this the ratio of turbulence intensity to centerline velocity deficit is constant, until the flow unlocks itself from this behavior when the local Reynolds number goes below about 500 and the viscous terms become important. When this happens the turbulence intensity ratio falls slowly until the x1/2 region is reached. No experimental data are available far enough downstream to provide unambiguous evidence for the x1/2 solution. The prediction that the flow should evolve into such a state, however, is confirmed by recent DNS results which reach the x1/2 solution at about 200 000 momentum thicknesses downstream. After this the turbulence intensity ratio is again constant, until box-size affects the calculation and the energy decays exponentially.

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“…10) The advantage of the boattail is that it shortens the recirculation length and reduces the near-wake intensity. 11) Consequently, the base pressure increases and base drag is diminished. Additionally, flow field on the boattail surface is also an important parameter that affects drag reduction.…”

Section: Introductionmentioning

confidence: 99%

Effect of Boattail Angle on Pressure Distribution and Drag of Axisymmetric Afterbodies under Low-Speed Conditions

Ambo

Chen

Nonomura

et al. 2019

Trans. Japan Soc. Aero. S Sci.

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This study is focused on the effect of boattail angle on the pressure distribution and drag force of axisymmetric afterbodies under low-speed conditions. Experiments were conducted on three conical boattails with angles of 10°, 14°and 20°. The diameter-based Reynolds number is approximately 4.3 © 10 4 under the experimental conditions. Two types of flows, a fully-attached flow (¢ = 10°) and a flow with a separation bubble (¢ = 14°, 20°), were observed. The aerodynamic drag measurements were conducted using both a strut-supported model and a support-free (levitated) model. The results show that boattail model with the angle of 20°has a relatively large effect on the pressure distribution. The pressure drag resulting from pressure distribution on the vertical plane indicates that the model with a boattail angle of 14°has the lowest drag. A good trend in agreement between afterbody drag (measured using pressure taps) and total aerodynamic drag (measured using the levitated system) was obtained. The effect of strut support on pressure distribution at different polar angles is also explained in this study.

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Wakes of three axisymmetric bodies at zero angle of attack

Cited by 18 publications

References 5 publications

The Effect of Boattail Angles on the Near-Wake Structure of Axisymmetric Afterbody Models at Low-Speed Condition

The Effect of Boattail Angles on the Near-Wake Structure of Axisymmetric Afterbody Models at Low-Speed Condition

Equilibrium similarity, effects of initial conditions and local Reynolds number on the axisymmetric wake

Effect of Boattail Angle on Pressure Distribution and Drag of Axisymmetric Afterbodies under Low-Speed Conditions

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