• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.142-146
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• 2006

The behavior of a hemisphere-cylinder flight vehicle at high angles of attack and side slip angles have been studied. $0^{\circ}{\sim}35^{\circ}$ angles of attack and $0^{\circ}{\sim}5^{\circ}$ side slip angles were selected as fright conditions at Mach No. 0.3. Flow changes from low angles of attack to high angles of attack were compared and analyzed. We changed from low to high angles of attack with small side slip angles. We compared normal, side and axial force coefficients among various test cases.

• Wind and Structures
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• v.32 no.5
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• pp.509-520
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• 2021

The streamlined box is a common type of girders for long-span suspension bridges. Spanning deep canyons, long-span bridges are frequently attacked by strong winds with large angles of attack. In this situation, the flow field around the streamlined box changes significantly, leading to reduction of the flutter performance. The wind fairings have different effects on the flutter performance. Therefore, this study examines the flutter performance of box girders with different wind fairings at large angles of attack. Computational fluid dynamics (CFD) simulations were carried out to extract the flutter derivatives, and the critical flutter state of a long-span bridge was determined. Further comparisons of the wind fairings were investigated by a rapid method which is related to the input energy by the aerodynamic force. The results show that a reasonable type of wind fairings could improve the flutter performance of long-span bridges at large angles of attack. For the torsional flutter instability, the wind fairings weaken the adverse effect of the vortex attaching to the girder, and a sharper one could achieve a better result. According to the input energies on the girder with different wind fairings, the symmetrical wind fairings are more beneficial to the flutter performance

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.1-11
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• 2021

Performance of a NACA 63₄-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA ≤ 30° at a Reynolds number of 10⁵. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.3-7
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• 2007

The characteristics of asymmetric vortex and side force of tangent-ogive-cylinder flight vehicle at high angles of attack have been performed by using upwind Navier-Stokes method with the ${\kappa}-{\omega}$ turbulence model. And Asymmetric transition positions are considered for generation of asymmetric vortex.

• Wind and Structures
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• v.24 no.5
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• pp.447-464
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• 2017

The flutter instability is one of the most important themes need to be carefully investigated in the design of long-span bridges. This study takes the central-slotted ideal thin flat plate as an object, and examines the characteristics of unsteady surface pressures of stationary and vibrating cross sections based on computational fluid dynamics (CFD) simulations. The flutter derivatives are extracted from the surface pressure distribution and the critical flutter wind speed of a long span suspension bridge is then calculated. The influences of angle of attack and the slot ratio on the flutter performance of central-slotted plate are investigated. The results show that the critical flutter wind speed reduces with increase in angle of attack. At lower angles of attack where the plate shows the characteristics of a streamlined cross-section, the existence of central slot can improve the critical flutter wind speed. On the other hand, at larger angles of attack, where the plate becomes a bluff body, the existence of central slot further reduces the flutter performance.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.4
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• pp.485-492
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• 2002

The present study is aimed to reveal macroscopic aerodynamic characteristics of two-dimensional rectangular prisms with three aspect ratios(D/H=1, 2 and 3) and six angles of attack($0^{circ}, 10^{circ}, 13.5^{circ}, 20^{circ}, 30^{circ} and 45^{\circ}$). The Reynolds number is fixed as $1\times10^4$. The SOLA-based revised finite difference method for the conservation form on irregular grid was adopted as a new numerical method. Instantaneous flow patterns at $45^{\circ}$ in case of D/H=2 and D/H=3 show larger asymmetric wake development which is closely related to the sharp decrease of drag coefficients at higher angles of attack range. Vorticity propagation into enlarged wake region is conjectured to be responsible for this phenomenon. The Strouhal number is found to be sensitive to the angle of attack at higher aspect ratios(D/H=2 and 3).

• Wind and Structures
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• v.34 no.2
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• pp.173-183
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• 2022

The galloping of iced conductors has long been a severe threat to the safety of overhead transmission lines. Compared with normal transmission lines, the ultra-high-voltage (UHV) transmission lines are more prone to galloping, and the damage caused is more severe. To control the galloping of UHV lines, it is necessary to conduct a comprehensive analysis of galloping characteristics. In this paper, a large-span 1000-kV UHV transmission line in China is taken as a practical example where an 8-bundled conductor with D-shaped icing is adopted. Galerkin method is employed for the time history calculation. For the wind attack angle range of 0°~180°, the galloping amplitudes in vertical, horizontal, and torsional directions are calculated. Furthermore, the vibration frequencies and galloping shapes are analyzed for the most severe conditions. The results show that the wind at 0°~10° attack angles can induce large torsional displacement, and this range of attack angles is also most likely to occur in reality. The galloping with largest amplitudes in all three directions occurs at the attack angle of 170° where the incoming flow is at the non-iced side, due to the strong aerodynamic instability. In addition, with wind speed increasing, galloping modes with higher frequencies appear and make the galloping shape more complex, indicating strong nonlinear behavior. Based on the galloping amplitudes of three directions, the full range of wind attack angles are divided into five galloping regions of different severity levels. The results obtained can promote the understanding of galloping and provide a reference for the anti-galloping design of UHV transmission lines.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.4 s.148
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• pp.460-466
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• 2006

The three-dimensional RANS equations were applied to analyze the flow field of a submarine. To validate the code, the DARPA SUBOFF bare hull and an eliipsoid at angles of attack of $10^{\circ}\;and\;30^{\circ}$ were simulated and good agreement with experiments was obtained. After the code validation, the flows over the full configuration of DARPA SUBOFF model having a fairwater and four stern appendages were simulated at four angles of attack $(0^{\circ},\;10^{\circ},\;20^{\circ},\;30^{\circ})$ and three yaw angles $(10^{\circ},\;20^{\circ},\;30^{\circ})$ Specifically, the pressure contours and streamlines of fairwater and stern appendage were compared as the angle of attack and yaw angle changed. The variations of hydrodynamic forces were also calculated.

• Wind and Structures
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• v.32 no.3
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• pp.239-248
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• 2021

In this study, three airfoil families, NACA, FX and S, in each case three from each series with different shapes were investigated at different angles of attack using Computational Fluid Dynamics (CFD) method. To verify the CFD model, simulation results of the NACA 0012 airfoil was compared against the available experimental data and k-ω SST was used as the turbulence model. Lift coefficients, lift to drag ratios and pressure distributions around airfoils were obtained from the CFD simulations and compared each other. The simulations were performed at three Reynolds numbers, Re=2×105, 1×106and 2×106, and angle of attack was varied between -6 and 12 degrees. According to the results, similar lift coefficient values were obtained for symmetric airfoils reaching their maximum values at similar angles of attack. Maximum lift coefficients were obtained for FX 60-157 and S 4110 airfoils having lift coefficient values around 1.5 at Re=1×106 and 12 degrees of angle of attack. Flow separation occurred close to the leading edge of some airfoils at higher angles of attack, while some other airfoils were more successful in keeping the flow attached on the surface.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.465-471
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• 2000

The flow characteristics around an elliptic cylinder with axis ratio of AR=2 located near a flat plate were investigated experimentally to study the interaction between the cylinder wake and the turbulent boundary layer. The pressure distributions on the cylinder surface and on the flat plate were measured with varying the angle of attack of the cylinder. In addition, the velocity profiles of wake behind the cylinder were measured using a hot-wire anemometry As the angle of attack increases, the location of peak pressure on the windward and leeward surfaces of the cylinder moves toward the rear and front of the cylinder, respectively. At positive angles of attack, the position of the minimum pressure on the flat plate surface is moved downstream, but it is moved upstream at negative angles of attack. With increasing the angle of attack, the vortex shedding frequency is gradually decreased and the critical angel of attack exists in terms of the gap ratio. By installing the elliptic cylinder at negative angle of attack, the turbulent boundary layer over the flat plate is disturbed more than that at positive incidence. This may be attributed to the shift of separation point on the lower surface of the cylinder according to the direction of the angle of attack.