• Journal of the Korean Society for Aviation and Aeronautics
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• v.28 no.2
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• pp.12-17
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• 2020

Even though the benefit of flight at high angle-of-attack is to be able to reduce the speed of flight and maneuvers in complex flight environment, the flight at high angle-of-attack, however, is easy to be in stall which is characterized by sever unsteady flow separation over an airfoil. Current unsteady numerical analysis using DES was conducted to predict the aerodynamic characteristics of a NACA 0021 airfoil at high angle-of-attack conditions. And this provides the comparison with the steady numerical one with the typical turbulence models. The unsteady calculation by DES is appropriate in terms of predicting the aerodynamic performance of NACA 0021 airfoil at high angle-of-attack conditions.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.60-66
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• 2010

Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.101-108
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• 2002

A numerical simulation of an incompressible cavity flow is conducted. Two dimensional Navier-Stokes equations are integrated using staggered grid and a finite volume method with C-QUICK scheme for spatial derivatives and fully implicit scheme for the time derivatives. SIMPLE-C algorithm is employed to solve the pressure field. Computational results show that the third eddy is generated in the shear layer mode but not in the steady mode. This signifies that the third eddy plays an important role in cavity flow stability. As a means to control the flow, jet blowing is applied to a position below the cavity upstream edge. Effects of flow control parameters on the stability such as the frequency, the phase, and the velocity magnitude are reported.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.127-138
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• 1999

In this study steady state solutions of cavity flows driven by two moving walls are studied. The north and east walls of the cavity are movable where as the remaining two walls are fixed in space. Numerical experiments for three different driving schemes for moving walls are done at two different Reynolds numbers of Re=40 and 400. The first scheme is to accelerate north and east walls simultaneously. In the second one, the north wall is started first and the east wall is accelerated later. In the third one the east wall starts first. It is usually expected that all these three cases yield the same steady state solution after sufficiently long time. However, present numerical experiments show that such a usual belief is valid only when the Reynolds number is low enough (Re=40). At higher Reynolds number (Re=400), the flow develops to three different steady states depending on the history of the boundary condition change.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.117-120
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• 2005

The present study describes unsteady flow phenomena generated in a supersonic flow passing over a rectangular cavity and suggests a way of control of pressure oscillation, doing harm to overall performance and stable operation of aerodynamic and industrial applications. The three-dimensional, unsteady, compressible Navier-stokes equations are numerically solved based on a fully implicit finite volume scheme and large eddy simulation. The cavity flow are simulated with and without control methods, including a triangular bump and blowing jet installed near the leading edge of the cavity. The results show that the pressure oscillation is attenuated by both control techniques, especially near the trailing edge of cavity.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.160.2-160
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• 2001

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.161.1-161
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• 2001

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.474-482
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• 2007

An analysis is made for flow and rocket motion during a supersonic separation stage of an air-launching rocket(ALR) from the mother plane. Three-dimensional compressible Navier-Stokes equations are numerically solved to analyze the steady/unsteady flow fields around the rocket which is being separated from the mother plane configuration(F-4E Phantom). Simulation results clearly demonstrate the effect of shock-expansion wave interaction around both of the rocket and the mother plane. To predict the behavior of the ALR by the change of the center-of-gravity, three cases of numerical analysis are performed. As a result, a design-guideline of supersonic air-launching rockets for safe separation is proposed.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.58-66
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• 1999

The flow characteristics of supersonic ejectors is often subject to compressibility, unsteadiness and shock wave systems. The numerical works carried out thus far have been of one-dimensional analyses or some Computational Fluid Dynamics(CFD) which has been applied to only a very simplified configuration. For the design of effective ejector-pump systems the effects of secondary mass flow on the supersonic ejector flow should be fully understood. In the present work the supersonic ejector-pump flows with a secondary mass flow were simulated using CFD. A fully implicit finite volume scheme was applied to axisymmetric compressible Navier-Stokes equations. The standard two-equation turbulence model was employed to predict turbulent stresses. The results obtained showed that the flow characteristics of constant area mixing tube types were nearly independent of the secondary flow rate, but the flow fields of ejector system with the second-throat were strongly dependent on the secondary flow rate due to the effect of the back pressure near the primary nozzle exit.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.310-313
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• 2006

The present study aims at investigating the effectiveness of a new passive cavity flow control technique, sub-cavity. The characteristics of cavity flow oscillation with the device are compared with those with other control techniques tested previously, including a triangular bump and blowing jet. In the computation, the three-dimensional, unsteady Navier-Stokes equations governing the supersonic cavity flow are solved based on an implicit finite volume scheme spatially and multi-stage Runge-Kutta scheme temporally. Large eddy simulation (LES) is carried out to properly predict the turbulent features of cavity flow. The present results show that the pressure oscillation near the downstream edge dominates overall time-dependent cavity pressure variations, and the amplitude of the pressure oscillation can be reduced in the presence of a sub-cavity.