• 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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1407-1414
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• 1988

Deviation angles are predicted by numerical calculation of three-dimensional compressible flow through the rotating blade row in axial flow compressor. Three-dimensional flow fields are analyzed by the quasi three-dimensional combination of blade-to blade surfaces and hub-to shroud stream surfaces and calculated by the finite element method in the cyclic calculation of both stream surfaces. In the blade-to blade calculations the method of boundary stream line correction is used and in the hub-to shroud calculations the loss effects due to viscous flow are included. The computational results are compared with the available experimental one. It is shown that the computational results from blade-to-blade flow calculation are correct for incompressible, compressible low subsonic and high subsonic flow at the inlet, and the loss effects on the deviation angle can be neglected in the range of the subsonic flow less than the critical Mach number for the axisymmetric flow and even for 3-D non-axisymmetric flow with loss. And it is found that the present results are better agreed with the experimental data than Lieblein's one.

• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.61-66
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• 1998

An inverse method for the subsonic and transonic airfoil design was developed using the Euler equations. Two testcases were performed. One was a design of the supercritical airfoil, aiming to be used for the Korean mid-sized (100 passengers class) transport aircraft. The other was the design of an airfoil showing a good cruising performance (L/D ratio) in the high subsonic/transonic flow regimes. These testcases demonstrated the efficiency and the robustness of the developed method.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.1
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• pp.1-7
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• 2016

Most of the work has been done till now focused on flows over wall mounted cavities in a straight wall where the incoming flow is uniform. However, the investigation on such kind of flow over a cavity mounted on the curved walls has been seldom reported in the existing literatures. In the present study, the numerical analysis was performed to investigate the cavity flow mounted on the curved walls. The effects of wall shape, the curvature radius and the flow Mach number, were investigated for high-subsonic flows. The results show that the static pressure of cavity floor increases as the L/R increases. This effect is found to be more significant when the flow Mach number is higher. The cavity drag for the curved walls are higher as compared with that of straight wall.

• 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..

• International Journal of Aeronautical and Space Sciences
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• v.14 no.3
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• pp.201-209
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• 2013

Much numerical and experimental research has been done for the flow around an oscillating airfoil. The main research topics are vortex shedding, dynamic stall phenomenon, MAV's lift and thrust generation. Until now, researches mainly have been concentrated on analyzing the wake flow for the variation of frequency and amplitude at a low angle of attack. In this study, wake structures and acoustic wave propagation characteristics were studied for a plunging airfoil at high angle of attack. The governing equations are the Navier-Stokes equation with LES turbulence model. OHOC (Optimized High-Order Compact) scheme and 4th order Runge-Kutta method were used. The Mach number is 0.3, the Reynolds number is, and the angle of attack is from $20^{\circ}$ to $50^{\circ}$. The plunging frequency and the amplitude are from 0.05 to 0.15, and from 0.1 to 0.2, respectively. Due to the high resolution numerical method, wake vortex shedding and pressure wave propagation process, as well as the propagation characteristics of acoustic waves can be simulated. The results of frequency analysis show that the flow has the mixed characteristics of the forced plunging frequency and the vortex shedding frequency at high angle of attack.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.46-53
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• 1998

An inverse method for the subsonic and transonic airfoil design was developed using the Euler equations. Two testcases were performed. One was a verification of the method using the supercritical airfoil of the Korean mid-sized (100 passengers class) transport aircraft. The other was the design of an airfoil showing a good cruising performance (L/D ratio) in the high subsonic flow regime. These testcases demonstrated the efficiency and the robustness of the design method in the present study.

• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.3-10
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• 1995

The compressible laminar and turbulent viscous flow on a slender body in supersonic speed as well as subsonic speed has been numerically simulated at high angle of attack. The steady and time-accurate compressible thin-layer Navier-Stokes code based on an implicit upwind-biased LU-SGS algorithm has been developed and specifically applied at angles of attack of 20, 30, 40 deg, respectively. The modified eddy-viscosity turbulence model suggested by Degani and Schiff was used to simulate the case of turbulent flow. Any geometric asymmetry and numerical perturbation have not been intentionally or artificially imposed in the process of computation. The purely numerical results for laminar and turbulent cases, however, show clear asymmetric formation of vortices which were observed experimentally. Contrary to the subsonic results, the supersonic case shows the symmetric formation of vortices as indicated by the earlier experiments.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.491-496
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• 2000

The physics of the flow field surrounding an engine nacelle afterbody is very complex. A high pressure jet from the nozzle interacts with the external flow and causes upstream influence on the afterbody surface field. At certain conditions, the nozzle boundary layer can separate, either by shock wave interaction or by adverse pressure gradient effect, resulting in a severe drag penalty. Furthermore, a finite afterbody base implies a recirculating flow region. A flow modeling method has been developed to analyze the flow in the annular base(rear-facing surface) of a circular engine nacelle flying at subsonic speed but with a supersonic exhause jet. Real values of exhaust gas properties and temperature are included.

• Journal of ILASS-Korea
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• v.24 no.1
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• pp.27-34
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• 2019

An experimental study on the spray characteristics of aerated-liquid jets discharged from effervescent injectors to a subsonic crossflow was conducted to investigate effects of a gas to liquid mass ratio (GLR) and a ratio of the orifice length to the diameter (L/d). The present effervescent injectors consist of a plain orifice injector and an aerator. To analyze breakup length and spray trajectory, instantaneous spray images were taken by a high speed camera. As the GLR increased, the spray penetration became higher under the same liquid mass flow rate and the breakup length became shorter due to the bubble expansion or the annular liquid film breakup. To predict the spray trajectory of two-phase flow jets into the crossflow, the homogeneous and the separated flow models were compared.