• 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.

• Atmosphere
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• v.24 no.2
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• pp.207-223
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• 2014

The bogussing method was further developed by incorporating the asymmetric component into the symmetric bogus tropical cyclone of the Structure Adjustable Balanced Vortex (SABV). The asymmetric component is separated from the disturbance field associated with the tropical cyclone by establishing local polar coordinates whose center is the location of the tropical cyclone. The relative importance of wave components in azimuthal direction was evaluated, and only two or three wave components with large amplitude are added to the symmetric components. Using the Weather Research and Forecast model (WRF), initialized with the asymmetric bogus vortex, the track and central pressure of tropical cyclones were predicted. Nine tropical cyclones, which passed over Korean peninsula during 2010~2012 were selected to assess the effect of asymmetric components. Compared to the symmetric bogus tropical cyclone, the track forecast error was reduced by about 18.9% and 17.4% for 48 hours and 72 hours forecast, while the central pressure error was not improved significantly. The results suggest that the inclusion of asymmetric component is necessary to improve the track forecast of tropical cyclones.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.8-13
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• 2008

A supersonic viscous flow over a five-degree half-angle cone is studied computationally with three-dimensional Navier-Stokes equations. Steady asymmetric solutions show that the asymmetric flow separation is caused by convective instability. The effects of angle of attacks, Reynolds numbers, and Mach numbers have been investigated and it is found that those factors affect the generation of the side force. The side force has the maximum value at ${\alpha}=22^{\circ}$, while over ${\alpha}=22^{\circ}$, asymmetric vortex becomes transient, which results in the unsteady shedding. At the angle of attack of 22 degrees, the side force increases with Reynolds number and decreases with Mach number. The increase of the side force stops over the critical Reynolds number for the present configuration.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.5
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• pp.607-612
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• 2013

The effect of the flow actuator on the asymmetric vortex structure around the ogive-cylinder body with fineness ratio of 4 flying at the speed of Mach 0.1 at angle of attack of 50 degree is studied. The ogive-cylinder model is developed with the actuator placed near the nose tip and numerically simulated using the in-house CFD code named KFLOW. The numerical simulation employs two different actuator modeling: one is the boundary condition given by blowing normal to the surface and another shearing on the surface. The numerical simulation reveals that response of the vortex structure to the actuation is dependent on the type of modeling as well as the strength and direction of the actuation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.335-338
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• 2007

In the case of an antiaircraft missile, high angle of attack flight capability is required to get the agile maneuverability in a supersonic flow. Even through a symmetric slender body does not have side slip, asymmetric vortex is generated at high angle of attack conditions. This asymmetric vortex produces unnecessary side force and yawing moment; hence, these effects deteriorate directional stability. In this study, the numerical analysis of asymmetric vortices around the slender body was conducted at high angle of attack supersonic flow. In order to simulate the vortices, a bump is installed on the nose of the slender body. As a result of the numerical analysis, the asymmetric vortices around the slender body could be simulated.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.171-176
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• 2007

Supersonic viscous flow over a 5 degree half angle cone studied computationally with three-dimensional Navier-Stokes equations. Steady asymmetric solutions of 5-deg half angle cone show that the asymmetric flow separation is caused by convective instability. The angle of attack, Reynolds number, and Mach number affected the side force variation that is caused by asymmetric vortical flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.8
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• pp.2122-2130
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• 1993

A numerical and experimental study has been performed on the flow in a shallow rectangular tank accompanying a vortex shedding. The model is composed of a rectangular tank with a vertical plate with a length half the width of the tank. The tank is subject to a horizontal sinusoidal oscillation. The numerical analysis shows that the pattern of vortex shedding changes considerably when the Reynolds number $R_e$ is varied from 500 to 7500. It is symmetric for $R_e$ <1500 and asymmetric for $R_e$ > 1500. The kinetic energies of the right-hand and left-hand sides of the vertical plate are used to quantify the degree of the asymmetry. Experimental visualization is carried out at $R_e$ = 3876 and 52000. The development of the streamline pattern at $R_e$ = 3876 is in closer agreement with the numerical result at $R_e$ = 1000 than that at $R_e$ =3876. The asymmetric pattern is observed at $R_e$ = 52000.

• Journal of computational fluids engineering
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• v.13 no.4
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• pp.39-44
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• 2008

Numerical simulations of laminar flow over a sphere are conducted to investigate the effect of the Reynolds number on the characteristics of vortex shedding. The Reynolds numbers considered are between 300 and 475, covering unsteady planar-symmetric and asymmetric flows. Results show that the unsteady planar-symmetric flow can be categorized into two different regimes: single-frequency regime and multiple-frequency regime. The former has a single frequency component due to periodic shedding of the vortices with the same strength in every shedding cycle, while the latter has multiple frequency components due to cycle-to-cycle variation in the strength of shed vortices with the shedding angle fixed. The multiple-frequency planar-symmetric flow, which is newly found in the present study, occurs at Re=330${\sim}$360 between the single-frequency planar-symmetric flow and the asymmetric flow. On the other hand, the asymmetric flow occurs at Re${\geq}$365, where the vortices shed from the sphere show variation both in strength and shedding angle unlike the planar-symmetric flow. Also, it is shown that the breaking of planar symmetry is closely related to the imbalance of vortical strength between a pair of streamwise vortices.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.33-38
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• 2008

Numerical investigation of asymmetric vortices at high angles of attack subsonic flow is performed using three-dimensional Navier-Stokes equations. A small bump has been carefully selected and attached near the nose of an ogive cylinder to simulate symmetric vortices. Selected bump shape does develop asymmetric vortices and is verified using Lamont's experimental results. By changing the angle of attack, Reynolds numbers, and Mach numbers, the characteristics of asymmetric vortices are observed. The angle of attack which contributes significantly to the generation of asymmetric vortices are over 30 degrees. By increasing Mach number and Reynolds number asymmetric vortices, hence the side forces show decreasing trend..

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.5
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• pp.713-721
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• 2001

Characteristics of the conical vortices on the roof corner of a rectangular prism have been investigated by using a PIV(Particle Image Velocimetry) technique. The Reynolds number based on the free stream velocity and the height of the model was 5.3$\times$10$^3$. The mean, instantaneous velocity vector fields, vorticity fields, and turbulent kinetic energy distribution were measured for two different angles of attack, 30$^{\circ}$and 45$^{\circ}$. The PIV measurements clearly observed not only the conical main vortex and the secondary vortex but also the tertiary vortex which is firstly reported in this paper. Asymmetric formation of the corner vortex for the case of 30$^{\circ}$angle of attack produces relatively the high magnitude of vorticity and turbulent kinetic energy around the bigger vortex which generates the peak suction pressure on the roof. Fairly symmetric features of the roof vortex are observed in the case of 45$^{\circ}$angle of attack, however, the dynamic characteristics are proved to be asymmetric due to the rectangular shape of the roof.