• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2704-2707
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• 2008

We perform an active control on flow over a circular cylinder using a synthetic jet at Re=3900. The synthetic jet is issued from a cavity located inside the cylinder, generating a train of vortices near the surface. These vortices interact with and weaken the main vortices, resulting in drag reduction at a high frequency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1418-1425
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• 1999

Flow over a protruding surface is investigated using numerical simulation. We consider flow between two parallel plates with a cube mounted on one side of the channel. As the flow approaches the cube, the adverse pressure gradient produces three-dimensional boundary-layer separation, resulting In the formation of horseshoe vortices. The objective of our study is to clarify both the steady and the unsteady characteristics of the vortex system. As the Reynolds number increases, the structure of the vortices near the cube becomes complex and the number of vortices increases. The distribution of skin friction on the cube-mounted wall reflects the effect of the horseshoe vortices. All these results are consistent with the experimental findings currently available.

• Journal of Institute of Convergence Technology
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• v.6 no.2
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• pp.21-24
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• 2016

Accurate simulation of wakeshapes behind a wing is important for the performance prediction of the aircraft and the wake hazard problem in the airport. In the present study, wakeshapes behind a wing inside tunnels are simulated in regard to the development of wing-in-ground effect vehicles. A discrete vortex method with a nonplanar ground modelling is used for the simulation. It was found that the wingtip vortices move toward outboard directions when the wing is in ground effect. When the wing is placed inside tunnels, the wingtip vortices move along the tunnel wall with counter clockwise direction. As the gap between the wingtip and the tunnel decreases, the wingtip vortices move further along the tunnel wall. Both vortices from bothsides of the wing will murge, which will be studied in future using a viscous computation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.91-94
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• 2003

An experimental study has been carried out in a supersonic blow-down wind tunnel for examining the influence of streamwise vortices on normal shock-wave/boundary layer interaction. It has been reported by the earlier investigator the streamwise vortices generated by the blowing jets can significantly suppress the shock-induced separation and reduce the wave drag. The blowing jets generate the streamwise vortices with 45$^{\circ}$ angle in the spanwise direction. The shock waves are visualized by a Schlieren optical system. Appropriate measurement systems are provided for the characterization of shock wave/boundary layer interaction. The chamber pressure ratio and blowing pressure ratio are varied from 1.5 to 2.4 and 1.0 to 2.0 respectively.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.404-409
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• 2000

Characteristics of secondary vortices is topologically investigated in the near-wake region of a circular cylinder where the Taylor hypothesis does not hold. The three-dimensional flow fields in the wake-transition regime were measured by a time-resolved PIV. For the analysis in a moving frame of reference, the convection velocity of the Karman vortices is evaluated from the trajectory of vortex center which is defined as the centroid of the vorticity field. Then, a saddle point is obtained by applying the critical point theory. Science the distributions of fluctuating Reynolds stresses defined by triple-decomposition are closely related with the existence of secondary vortices. the physical meaning of them is explained in conjunction with vortex center and saddle point trajectories. Finally, the temporal evolution of streamwise vortex is also discussed.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.11-12
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• 2006

We conducted a direct numerical simulation (DNS) to establish database for the purpose of improvement of practical method which is applicable to cavitating turbulent flows. Cavitations caused by spanwise and streamwise vortices, which are typical features in high shear layer, is represented by a simple model and interaction between vortices and cavities is reproduced. The qualitative agreement between computation and experiment are reasonable. Cavities due to streamwise vortices in a shear layer seem to attenuate turbulent eddies.

• Journal of Aerospace System Engineering
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• v.10 no.1
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• pp.1-7
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• 2016

During flight of the aircraft, the vortex merging phenomenon appears under the certain condition between co-rotating vortices which were generated at the wing tip and lifting-surface. And then these merged vortices at both sides show counter-rotating pattern to affect on the downstream of the aircraft. In this paper, the numerical simulations are conducted assuming this phenomenon in two-dimensional co-rotating or counter-rotating vortices pairs. Two-dimensional incompressible Navier-Stokes equations were converted into Vorticity-Streamfunction form and the Galerkin spectral method was adopted. The third order Runge-Kutta method was used for time integration. The effects on the vortex merger and degree of vortex merger were investigated according to time, Reynolds number, and changes in the distance between two vortices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.900-908
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• 2009

Numerical simulation has been carried out to investigate the influence of radial temperature gradient on the Taylor Vortex flow. Varying the Grashof number, we study the detailed flow and temperature fields. The current numerical results show good agreement with the experimental results currently available. It turns out that wavy spiral vortices are generated by increasing temperature gradient. We classify flow patterns for various Grashof numbers based on the characteristics of flow fields and spiral vortices. The correlation between Grashof number with wave number shows that the spiral angle and size of Taylor vortices increase with increasing temperature gradient. Temperature gradient does not have a great influence on the heat transfer rate of the cylinder surfaces.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.578-586
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• 2006

Numerical simulations are carried out to investigate the thermal effects of the gravitational potential on the centrifugal instability of a Taylor-Couette flow, and to further study the detailed flow fields and flow bifurcations to spiral vortices. The effects of centrifugal potential on the centrifugal instability are also investigated in the current study. Spiral vortices have various types of mode depending on Grashof number and Reynolds number. The correlation of Richardson number with the spiral angle of the spiral vortices shows that the structure of the spiral vortices strongly depends on the Richardson number. The heat transfer rate of the inner cylinder increases with increasing Grashof number. It is also confirmed that the torque required to rotate the inner cylinder increases as Grashof number increases.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.667-672
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• 2000

The Characteristics of the conical vortices on the roof surface of a low-rise building has been investigated by using a PIV(Particle Image Velocimerty) technique. The scaled model of TTU building with 1:92 scaling ratio was used. The Reynolds number based on the free stream velocity and the length of the model was $1.96{\times}10^5$. When the angle of attack for the building model is $45^{\circ}$, the conical vortices are occurred symmetrically and the center of vortices are changed with respect to the angle of the approaching flow. The rotating direction of the conical vortices found to be counter-rotating. The secondary vortex motions are investigated using the instantaneous flow field data.