• International Journal of Aeronautical and Space Sciences
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• 제13권1호
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• pp.27-33
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• 2012

The relationship between the excitation frequency and the vortex shedding frequency is analyzed during the oscillation of the circular cylinder. Two-dimension unsteady Navier-Stoke's equation is calculated by using the Optimized High Order Compact (OHOC) scheme. The flow condition is Mach number 0.3 and Reynold's number 1000. From the results acquired by calculation, it can be inferred that, when the excitation frequency is near the vortex shedding frequency at the fixed cylinder wake, the oscillation frequency of lift and drag coefficients appears to lock-on. The lock-on refers to a phenomenon in which the aerodynamic coefficient appears as one primary oscillation frequency through excitation and its amplitude is amplified. In the non-lock-on zone, the excitation frequency is not in the lock-on mode anymore and beat is formed in which two or more primary oscillation frequencies of the aerodynamic coefficient are mixed together.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.106-112
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• 2000

Axial fans are widely used in heavy machines due to their ability to produce high flow rate for cooling of engines. At the same time. the noise generated by these fans causes one of the most serious problems. This work is concerned with the low noise technique of discrete frequency noise. The prediction model. which allowed the calculation of acoustic pressure at the blade passing frequency and it's harmonics. has been developed by Farrasat. This theory is founded upon the acoustic radiation of unsteady forces acting on blade. To calculate the unsteady resultant force over the fan blade. Time-Marching Free-Wake Method are used. The fan noise of fan system having unsymmetric engine-room is predicted. In this paper, the discussion is confined to the performance and discrete noise of axial fan and front part of engine room in heavy equipments.

• 한국화재소방학회논문지
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• 제11권2호
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• pp.19-24
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• 1997

화재 모델에서 구한 가스 의 온도를 이용하여 비정상 열전도 방정식의 수치해석을 하면 유한 제어 체적을 계산할 수 있으며 가열 온도와 저감율로 열에 의한 압축 및 휨 강도의 저하값을 계산할 수 있다. 또한 이 방법을 이용하여 콘크리트 구조물(기둥, 보등)의 안전성 평가에 잘 적용할수 있었다.할수 있었다.

• Nuclear Engineering and Technology
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• 제41권9호
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• pp.1191-1204
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• 2009

In this study, a CFD methodology is employed to address the problem of the prediction of the flow in a T-junction. An Unsteady Reynolds Averaged Navier-Stokes (URANS) approach has been selected for its low computational cost. Moreover, Unsteady Reynolds Navier-Stokes methodologies do not need complex boundary formulations for the inlet and the outlet such as those required when using Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS). The results are compared with experimental data and an LES calculation. In the past, URANS has been tried on T-junctions with mixed results. The biggest limit observed was the underestimation of the oscillatory behavior of the temperature. In the present work, we propose a comprehensive approach able to correctly reproduce the root mean square (RMS) of the temperature directly downstream of the T-junction for cases where buoyancy is not present.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.97-104
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• 1998

The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. Lowson's method is used to predict the acoustic pressure in a free field. A DVM(discrete vortex method) is used to model the centrifugal fan and to calculate the flow field. In order to compare the experimental data, a centrifugal fan and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.134-137
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• 2007

Aero-Heating phenomenon is one of the severe problems occurring in high speed missile flight. in the high speed flight, not only stagnation point but also aft body parts encounter high temperature related structural problems. But the phenomenon is not easy to predict accurately because unsteady calculation according to a flight trajectory is needed, and takes much time. In this Paper, a fast and precise scheme is introduced, which calculates heat flow and temperature by simple pressure field prediction on a missile.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.706-711
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• 2003

A numerical method is presented for computing unsteady incompressible two-phase flows with immersed solids. The method is based on a level set technique for capturing the phase interface, which is modified to satisfy a contact angle condition at the solid-fluid interface as well as to achieve mass conservation during the whole calculation procedure. The modified level set method is applied for numerical simulation of bubble deformation in a micro channel with a cylindrical solid block and liquid jet from a micro nozzle.

• 오토저널
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• 제6권4호
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• pp.46-53
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• 1984

The analysis of temperature distribution and change of metallic structures during water quench were presented by finite element method. In temperature calculation the equation of unsteady state hear conduction problem considering latent heat due to phase transformation was applied to finite solid cylinder, SM 45C of 40mm diameter and 40mm height. In metallic structure analysis iso-thermal transformation curve and the equations of evolution in pearlite-martensite transformation were applied. The calculated results upon temperature and metallic structures were agreed with those of experimental observations.

• Journal of Hydrospace Technology
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• 제2권2호
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• pp.57-67
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• 1996

The formulation for hybrid-QUICK scheme of convective transport terms in finite-volume calculation procedure is presented. Source terms are modified to apply the hybrid-QUICK scheme. Test calculations are performed for wall-driven cavity flow at Re=$10_2$, $10_3$, and $10_4$. These include the evaluation of boundary conditions approximated by third-order finite difference scheme. The stable and converged solutions are obtained without unsteady terms in the momentum equations. The results using hybrid-QUICK scheme show no difference with those using hybrid scheme at low Re ($=10_2$) and are better at higher Re ($10_3$, and $10_4$).

• 오토저널
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• 제7권1호
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• pp.24-34
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• 1985

The study of unsteady gas exchange processes in the inlet and exhaust systems of the single-cylinder 4-stroke cycle spark ignition engine is presented in this paper. The generalized method of characteristics including friction, heat transfer, change of flow area and entropy gradients was used for solving the equations defining the gas exchange process. The path line calculation was also conducted to allow for calculation of the gas composition and entropy change along the path lines, and of the variable specific heat due to the change of temperature and composition. As the result of the simulation, the properties at each point in the inlet and exhaust pipe, pressure and temperature in the cylinder, and charging efficiency were obtained. Pumping loss and residual gas fraction were also computed. The effect of engine speed, exhaust and inlet pipe length on the pumping loss and charging efficiency were studied showing that the results were in agreement with what has been known from experiments.