• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.62-70
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• 2001

Three-dimensional dynamic stall over an oscillating wing has been analyzed by using a compressible Navier-Stokes code. The code solved the thin-layer Navirer-Stokes equations with a second-order time accuracy for a semispan wing with 0.3048m chord, a NACA 0015 airfoil section, and zero twist Computations were made for a freestream Mach number of 0.29, a chord Reynolds number of 1.95$\times$10(sup)6 and a reduced frequency equal to 0.1. Numerical results were compared with experimental data which include the hysteresis of lift, drag and moment at various wing span. The comparison reveals the quantitative as well as qualitative nature of the three-dimensional dynamic stall.

• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.81-89
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• 2006

Two dimensional turbulent flow simulations on the low Mach number - high Reynolds number flow about the NACA 4412 airfoil are carried out as the airfoil approaches a ground. It has turned out that angle of attack between 2 and 8 degrees is recommended for the airfoil to utilize the benefit of ground effect. For the large angle of attack, the increment of lift due to the ground effect is faded away and negative aerodynamic effect such as destabilizing aspect in static longitudinal stability occurs and the separation point moves to forward as the airfoil approaches a ground.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.199-205
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• 2006

Two dimensional turbulent flow simulations on the low Mach number - high Reynolds number flow about the NACA 4412 airfoil are carried out as the airfoil approaches a ground. It has been turned out that angle of attack between 2 and 8 is recommended for the airfoil to utilize the benefit of ground effect. For the large angle of attack, the increment of lift due to the ground effect is eliminated and negative aerodynamic effect such as destabilizing aspect in static longitudinal stability are occurred as the airfoil approaches a ground.

• Journal of Mechanical Science and Technology
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• v.17 no.2
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• pp.280-287
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• 2003

The unsteady flow characteristics and the related noise of separated incompressible laminar boundary layer flows (Re$\sub$$\delta$/* = 614, 868, and 1,063) are numerically investigated. The characteristic lines of the wall pressure are examined to identify the primary noise source, related with the unsteady motion of the vortex at the reattachment point of the separation bubble. The generation and propagation of the vortex-induced noise in the separated laminar boundary layer are computed by the method of Computational Aero-Acoustics (CAA), and the effects of Reynolds number, Mach number and adverse pressure gradient strength are examined.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.300-305
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• 2001

The unsteady flow structure and the related noise generation, which are caused by the separation of a two-dimensional, incompressible, laminar boundary-layer on the flat plate under the influence of local adverse pressure gradient, are numerically examined. The characteristic lines of the wall pressure are examined to understand the unsteady behavior of vortex shedding near the reattachment point of the separation bubble. Also, the generation and propagation of the vortex-induced noise in the separated boundary-layer are calculated by the method of computational aero-acoustics (CAA), and the effects of Reynolds number, Mach number and the strength of the adverse pressure gradient on the unsteady flow and noise characteristics are examined.

• Journal of the Korean Society of Safety
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• v.15 no.1
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• pp.36-42
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• 2000

An experimental study was carried out to investigate the effects of inclined angles of channel on thermal stability of electronic components. In this study, it is focused on the natural convection heat transfer from an inclined parallel channel with discrete protruding heat sources. The material used for the inclined parallel channel was epoxy-resin, while air as the cooling fluid. Heat transfer phenomena for inclined angles of $\psi$=$15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$ and for the range of $9.52{\times}10^5/ were analyzed. The thermal fields in the channel were visualized by Mach-Zehnder interferometer. Also, local temperatures were measured by thermocouples along the channel wall and heat sources surface. As a result, for the range of $4.29{\times} 10^5/, a useful correlation of mean Nusselt number was proposed as a function of modified channel Rayleigh number.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.434-440
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• 2011

Oscillating airfoil haw been challenged for the dynamic stalls of airfoil am wind turbines at high angle of attach. Especially, the pressure oscillation has a huge effect on noise generation, structure damage, aerodynamic performance am safety, because the flow has strong unsteadiness at high angle of attack. In this paper, the unsteady aerodynamics coefficients were analyzed for the oscillating airfoil at high angle of attack around two dimensional NACA0012 airfoil. The two dimensional unsteady compressible Navier-Stokes equation with a LES turbulent model was calculated by OHOC (Optimized High-Order Compact) scheme. The flow conditions are Mach number of 0.2 and Reynolds number of $1.2{\times}10^4$. The lift, drag, pressure distribution, etc. are analyzed according to the pitching oscillation. Unsteady velocity field, periodic vortex shedding, the unsteady pressure distribution, and the acoustic fields are analyzed. The effects of these unsteady characteristics in the aerodynamic coefficients are analyzed.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.5
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• pp.580-588
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• 2006

Two-dimensional turbulent flows past a square cylinder and cavity noise are simulated by the finite difference lattice Boltzmann method with subgrid turbulence model. The method, based on the standard Smagorinsky subgrid model and a single-time relaxation lattice Boltzmann method, incorporates the advantages of FDLBM for handling arbitrary boundaries. The results are compared with those by the experiments carried out by Noda & Nakayama and Lyn et al. Numerical results agree with the experimental ones. Besides, 2D computation of the cavity noise generated by flow over a cavity at a Mach number of 0.1 and a Reynolds number based on cavity depth of 5000 is calculated. The computation result is well presented a understanding of the physical phenomenon of tonal noise occurred primarily by well-jet shear layer and vortex shedding and an aeroacoustic feedback loop.

• Journal of Ocean Engineering and Technology
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• v.21 no.3 s.76
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• pp.16-25
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• 2007

A comparative study on the turbulent flaw simulation and the potential flaw analysis has been performed. A law Mach number preconditioned Navier-Stokes solver, using the multi-block grid method and a panel method based on the velocity potential, have been developed and validated by comparison to the experimental data. The present numerical analysis methods are applied to the ground effect problem around the NACA 4412 airfoil. It has been confirmed that the potential flaw analysis on the ground effect, using the image method, is consistent, to some degree, with the viscous calculations for high Reynolds number flows.

• Journal of KSNVE
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• v.3 no.3
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• pp.245-251
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• 1993

The problem of sound radiation from infinite elastic beams under the action on harmonic moving line forces is studies. The reaction due to fluid loading on the vibratory response of the beam is taken into account. The beam is assumed to occupy the plane z=0 and to be axially infinite. The beam material and elastic foundation are assumed to be lossless and Bernoulli-Euler beam theory including a tension force (T), damping coefficient (C) and stiffness of foundation $(\kappa_s)$ will be employed. The non-dimensional sound power is derived through integration of the surface intensity distribution over the entire beam. The expression for sound power is integrated numerically and the results examined as a function of Mach number (M), wavenumber ratio$(\gamma{)}$ and stiffness factor $(\Psi{)}$. Here, our purpose is to explain the response of sound power over a number of non-dimensional parameters describing tension, stiffness, damping and foundation stiffness.