• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.121-126
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• 2001

An accelerating flow field through a compressor cascade is studied numerically by unsteady computational simulation. The two-dimensional Navier-Stokes equations for compressible flow is used for the study of unsteady high incidence angle flow, with preconditioning scheme to cover the wide range of Mach number and $\kappa-\omega$ model for the turbulent viscous flow analysis. A DCA(double circular arc) compressor blade is accelerated artificially in this study to understand the unsteady effect by comparing the present results with the existing steady-state experimental and computational results. Also, the accelerating flow field during the starting phase of gas turbine is studied with actual experimental data for the understanding of flow field and performance characteristics at off-design condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.556-561
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• 2003

Flight bodies are subject to highly unstable and severe flow conditions during taking-off and landing periods. In this situation, the flight bodies essentially experience accelerating or decelerating flows, and the aerodynamic characteristics can be completely different from those of steady flows. In the present study, unsteady aerodynamic characteristics of an aerofoil accelerating at subsonic speeds are investigated using a computational method. Two-dimensional, unsteady, compressible Navier-Stokes simulations are conducted with a one-equation turbulence model, Spalart-Allmaras, and a fully implicit finite volume scheme. An acceleration factor is defined to specify the unsteady aerodynamics of the aerofoil. The results show that the acceleration of the subsonic aerofoil generally leads to a variation in aerodynamic characteristics and it is more significant at angles of attack.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2115-2120
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• 2003

Many flight bodies are essentially imposed in gradually accelerating and decelerating free streams during taking-off and landing processes. However, the wing aerodynamics occurring in such a stream have not yet been investigated in detail. The objective of the present study is to make clear the aerodynamic characteristics of an aerofoil placed in the accelerating and decelerating free stream conditions. A computational analysis is carried out to solve the unsteady, compressible, Navier-Stokes equations which are discretized using a fully implicit finite volume method. Computational results are employed to reveal the major characteristics of the aerodynamics over the gradually accelerating aerofoil wings.

• 대한조선학회논문집
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• 제56권6호
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• pp.507-514
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• 2019

Computational studies of accelerating flow around 2D Circular Cylinder was performed to investigate characteristics of wake field and drag forces. Previous studies had revealed that drag on the cylindrical body in accelerating flow is much greater than that in the flow with constant velocity; however, the underlying physics on the drag increase has not been clearly investigated. In order to investigate the drag increase and its relationship with wake development, this study employed a finite-volume based CFD code, Fluent 13.0 with k-ω SST model for turbulence effects. Inflows are modeled with varied accelerations from 0.4905 to 9.81m/s². The drag computed in the present study is in good agreement with previous studies, and clearly shows the increase compared to the drag on the body in the flow with constant velocity. The results also show that drag crisis observed at high Reynolds number in the case of the flow with constant velocity is also found in the case of accelerating flow. The analysis for wake and recirculation length shows that conventional vortex shedding does not occur even at high Reynolds number and the drag increase is larger at higher acceleration.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.347-352
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• 2004

The unsteady aerodynamic characteristics of an aerofoil gradually accelerating or decelerating at subsonic speeds are investigated through two-dimensional, unsteady, compressible Navier-Stokes simulations. An acceleration factor is defined to provide various acceleration or deceleration characters of the time-dependent flow over the aerofoil. The results show that an increase in the absolute value of the non-dimensional acceleration factor leads to a lesser change in the location and range of flow featues such as shockwave and boundary layer separation in a specific time range. Generally, the gradual speed-up and speed-down of the subsonic aerofoil results in different aerodynamic characteristics whose changes are more significant at angles of attack.

• 한국관개배수논문집
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• 제4권2호
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• pp.38-47
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• 1997

In the final stage of seadike closing, the flow in the tidal gap changes rapidly to high accelerating flow, causing losses of construction materials. As the tidal velocity through the gap of an end dump contraction is highly nonuniform, flow equations on

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 춘계학술대회 논문집
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• pp.69-74
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• 2001

The Wells turbine has hysteresis characteristics in a reciprocating flow. In this paper, in order to understand unsteady flow characteristics of the Wells turbine, a sinusoidal flow condition is simulated. The flow conditions and hysteresis characteristics, including blade thickness, are investigated over a period of time. The pressure distributions along the blade surface are investigated at mid-span to clarify the cause of the hysteresis. The result has shown that the hysteresis characteristics become more pronounced as blade thickness becomes larger. The occurrence of these characteristics depends on the varying behavior of wakes between an accelerating flow and a develerating flow.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.497-500
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• 2005

This study was performed to evaluate the characteristics which are slump, air content and time of set in fresh concrete and compressive strength of hardened concrete containing slag powder and fly-ash. Replacement rate of FA is fixed on 10$\%$ and replacement rate of slag powder are 0$\%$, 20$\%$ and 30$\%$. Also AE water-reducing agents(standard type, accelerating type) are used. The results were as follows. (1)Slump flow of concrete using AE water-reducing agents is similar. Flowability is incresed when replacement rate of slag powder is increased due to slag powder's ball bearing reaction.(2)Time of set of concrete using accelerating type agent is more faster than that of concrete using standard type agent because of ettringite generation that promote setting.(3)Early strength of three-component concrete using accelerating type agent is higher than that using standard type agent. Therefore cumulative pore is reduced due to ettringite

• 한국유체기계학회 논문집
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• 제13권1호
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• pp.35-41
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• 2010

Experimental study on the flow field inside the nozzle for radial turbine was performed. At design point, the pressure is high and the Mach number is low at the pressure side of the nozzle inlet semi-vaneless space as the flow turns through the nozzle vanes. As the flow accelerates through the nozzle passage to the throat the pressure level at the pressure and suction sides becomes similar. The flow continued accelerating from the throat to the inlet of turbine wheel and the pressure field became uniform in the circumferential direction in the vaneless space. In high expansion ratio condition, strong favorable pressure gradient band region occurred just after the throat in the semi-vaneless space in the circumferential direction and the pressure became uniform in the circumferential direction after this band. In low expansion ratio condition, core flow acceleration is dominant after the throat and this non-uniform pressure field reached to the inlet of turbine wheel.

• 한국자동차공학회논문집
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• 제17권1호
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• pp.182-189
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• 2009

The noise from the sunroof can be divided into the low frequency buffeting noise and the high frequency turbulence noise generated when a car runs at the high driving speed. The wind deflector suppresses the buffeting noise generation by accelerating the vortex shedding from the front edge of sunroof opening, and guides the flow direction so that air can pass smoothly over the sunroof opening. To reduce the buffeting noise and the high frequency noise, it is very important to locate a deflector in a proper position depending on the driving speed and the sunroof opening width. The deflector's sectional shape also plays an important role in efficiently reducing the buffeting and high frequency noise. In this paper, we determined the optimum deflector's sectional shape and examined the flow characteristics behind a sunroof deflector through CFD analysis with changing the deflector height, the driving speed and the sunroof opening width. It is found that the deflector needs to be located in the higher location to control the buffeting noise by shedding the higher frequency vortices to accelerating vortices from the sunroof front edge. The deflector may act as a new noise source at the high driving speed, then it is desirable to put the deflector at the proper height to reduce the flow fluctuations and the noise generation. We also made a road test to verify CFD analysis results in this study.