• The Journal of the Acoustical Society of Korea
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• v.21 no.2
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• pp.134-141
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• 2002

In this paper, a free wake analysis based on the curved vortex element and CVC wake model is used to predict the aerodynamic performance and noise for HAWT. Also for prediction of RPM, a maximum value through a quadratic regression was suggested. And for a noise prediction, the broadband noise prediction method based on experimental equation was used. The curved vortex element uses a BCVE and an SIVE instead of a straight vertex element. In the CVC wake model, the vortex strengths are assumed to be constant along a span and a vortex filament. The free wake structure made by the curved vortex element and CVC was substituted for a vortex lattice, so it has an advantage for the less calculation time and a depiction of accurate wake structure. For the verification of this program, calculated results are compared with Mr. Kim's experiment model and Zond Z-40FS for performance and with WTS-4 and USWP models for noise. Good agreements are obtained between the predicted and the measured data for the performance and far-field noise spectra.

• The Journal of the Acoustical Society of Korea
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• v.39 no.2
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• pp.77-86
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• 2020

In this study, the Eulerian/Lagrangian one-way coupling method is proposed to predict flow noise due to Blade-Tip Vortex Cavitation (BTVC). The proposed method consists of four sequential steps: flow field simulation using Computational Fluid Dynamics (CFD) techniques, reconstruction of wing-tip vortex using vortex model, generation of BTVC using bubble dynamics model and acoustic wave prediction using the acoustic analogy. Because the CFD prediction of tip vortex structure generally suffers from severe under-prediction of its strength along the steamwise direction due to the intrinsic numerical damping of CFD schemes and excessive turbulence intensity, the wing-tip vortex along the freestream direction is regenerated by using the vortex modeling. Then, the bubble dynamics model based on the Rayleigh-Plesset equation was employed to simulate the generation and variation of BTVC. Finally, the flow noise due to BTVC is predicted by modeling each of spherical bubbles as a monople source whose strength is proportional to the rate of time-variation of bubble volume. The validity of the proposed numerical methods is confirmed by comparing the predicted results with the measured data.

• Journal of the Korean Society of Safety
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• v.22 no.1 s.79
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• pp.24-29
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• 2007

The effectiveness of a UV(ultra violet) disinfection system depends on the characteristics of the waste water, flow conditions, the intensity of UV radiation, the amount of time the microorganisms are exposed to the radiation, and the reactor configuration. The wast water flow conditions are important factors in the design of UV disinfection system from the point of enhancement view of UV disinfection. The turbulent energy intensity in the wake by the vortex shedding are effective for UV radiation. Therewith the effectiveness of vortex generator is considered as a enhancement of UV disinfection. The experimental results presented give important evidences and explain that it is possible to predict UV disinfection performance based on flow experiments. An experimental investigation of two types of the vortex generator is presented. The qualitative and quantitative evaluations of the wake are made by flow visualization using smoke wire method and the measurement of vortex frequencies in the wind tunnel. From the experiment, following results were obtained that the delta wing type vortex generator is more effective than circular type because of the higher vortex frequencies and the smaller drag.

• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.405-412
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• 2012

A flow control on airfoil installed a vortex cell for high efficiency wind turbine blade in stationary and dynamic stall conditions have been numerically investigated by solving the compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with Roe's flux-difference splitting and an implicit time-integration method coupled with dual time step sub-iteration. The computed result for the airfoil in the stationary showed that lift-drag ratio increases due to low pressure by the vortex cell. The oscillating airfoil with the vortex cell showed that the magnitude of hysteresis loop is reduced due to the enhanced vortex in the cell.

• Journal of the Korean earth science society
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• v.41 no.4
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• pp.344-355
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• 2020

Tropical cyclone scale vortices and associated Rossby waves were investigated numerically using high-resolution barotropic models on the global domain. The equations of the barotropic model were discretized using the spectral transform method with the spherical harmonics function as orthogonal basis. The initial condition of the vortex was specified as an axisymmetric flow in the gradient wind balance, and four types of basic zonal states were employed. Vortex tracks showed similar patterns as those on the beta-plane but exhibited more eastward displacement as they moved northward. The zonal-mean flow appeared to control not only the west-east translation but also the meridional translation of the vortex. Such a meridional influence was revealed to be associated with the beta gyre and the Rossby wave, which are formed around the vortex due to the beta effect. In the case of the basic zonal state of climatological mean, the meridional translation speed reached the maximum value when the vortex underwent recurving.

• Current Optics and Photonics
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• v.7 no.2
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• pp.127-135
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• 2023

Radially polarized beams with the ability to generate a sub-wavelength sized spot in a longitudinal field provides significant applications in microscopic imaging, optical tweezers, lithography and so on. However, this excellent property can also be achieved based on conventional circularly polarized beams. Here, we demonstrate its ability to create a strong longitudinal field by comparing the tight focusing characteristics of fractional-order vortex modulated radial polarized and left-handed circular polarized Bessel-Gauss beams. Additionally, the possibility of generating arbitrary fractional-order vortex modulated Bessel-Gauss beams with a strong longitudinal field is demonstrated. A special modulation method of left-handed circularly polarized Bessel-Gauss beams modulated by a fractional-order vortex is adopted creatively and a series of regulation laws are obtained. Specifically, the fractional-order phase modulation parameter n can accurately control the number of optical lobes. The ratio of the pupil radius to the incident beam waist β₁ can control the radius of the optical lobes. The first-order Bessel function amplitude modulation parameter β₂ can control the number of layers of optical lobes. This work not only adds a new modulation method for optical micromanipulation and optical communication, but also enriches the research on fractional vortex beams which has very important academic significance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.9-15
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• 2004

In this study the development of the two dimensional flowfield around an impulsively translated circular cylinder is numerically simulated using the diffusion vortex method. A detailed streamline pattern of fore wake and main wake of Re=1200, 9500 flowfields are investigated. The results of streamline pattern, the size of main wake and the axial velocities along the rear symmetry axis of the circular cylinder show good agreement with the reported experimental results. The long term wake delvelopment for Re=1200 flowfield was calculated up to ${\tau}=50$. The vortex shedding frequency shows the similar value as that of reported.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.55-66
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• 2004

In this paper a method for finding solutions of acoustic, vortex and entropy wave equations in a cylindrical tube with variable section area was suggested under the consideration of that the high frequency instability in a rocket engine combustion chamber is an acoustic phenomena, which Is coupled with combustion reaction. and that a combustion chamber and exhaust nozzle are usually shaped cylindrically As a consequence of that some method. which enable the mathematical analysis of the influence of entropy and vortex waves to acoustic wave. was suggested. According to the method reflection coefficients of acoustic wave on a supercritical nozzle was numerically calculated, through which it was presented that entropy or vortex waves can strengthen or weaken the reflection rate of acoustic wave.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.78-85
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• 2011

The Vortex-In-Cell(VIC) method combined with panel method is applied to the analysis of incompressible unsteady viscous flow. The dynamics of resulting flow is governed by the vorticity transport equation in Lagrangian form with vortex particle representation of the flow field. A regular grid which is independent to the shape of a body is used for numerical evaluation based on immersed boundary technique. With an introduction of this approach, the development and validation of the VIC method is presented with some computational results for incompressible viscous flow around two or three dimensional bodies such as wing section, sphere, finite wing and marine propeller.