• 대한기계학회논문집
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• 제9권5호
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• pp.555-563
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• 1985

본 논문에서는 원주(circular cylinder)가 균일속도장에 놓였을 때의 2차원적 인 난류후류유동 특성을 실험에 의해 조사하고, 근접후류에서의 주기적인 대규모 운동 에 의한 코히어런트구조가 하류에서 자체유사(selfpreserving)로 되어 가는 데 있어서 의 난류변동성분에 관한 해석을 위해 확률밀도함수, 자기상관계수, 파워스펙트럼 등과 같은 통계적 처리기법을 도입하고자 한다.

• 대한기계학회논문집
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• 제12권1호
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• pp.137-151
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• 1988

본 논문에서는 아래 평판은 높은 온도 $T_{h}$로 유지되고, 위의 평판은 낮은 온도 $T_{i}$로 유지되어 있을 때 온도차에 의하여 발생하는 난류 열대류 문제를 난류모델 방정식을 사용하여 수치적으로 해석하고자 한다.다.다.

• 한국전산유체공학회지
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• 제17권1호
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• pp.54-60
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• 2012

Transition prediction results are validated with experimental data obtained from a transonic wind tunnel for the KU109C airfoil. A Reynolds-Averaged Navier-Stokes code is simultaneously coupled with the transition transport model of Langtry and Menter and applied to the numerical prediction of aerodynamic performance of the KU109C airfoil. Drag coefficients from the experiment are better correlated to the numerical prediction results using a transition transport model rather than the fully turbulent simulation results. Maximum lift coefficient and drag divergence at the zero-lift condition with Mach number are investigated. Through the present validation procedure, the accuracy and usefulness of both the experiment and the numerical prediction are assessed.

• 대한기계학회논문집B
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• 제25권6호
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• pp.776-785
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• 2001

Hot-wire measurements are performed in boundary layers developing on a NACA0012 airfoil over which wakes pass periodically. The Reynolds number based on chord length of the airfoil is 2$\times$10(sup)5 and the wakes are generated by circular cylinders rotating clockwise and counterclockwise around the airfoil. This paper and its companion Part II describe the phenomena of wake-induced transition of the boundary layers on the airfoil using measured data; phase-and time-averaged streamwise mean velocities, turbulent fluctuations, integral parameters and wall skin frictions. This paper describes the background and facility together with results of time-averaged quantities. Due to the passing wake with mean velocity defects and high turbulence intensities, the laminar boundary layer is periodically disturbed at the upstream station and becomes steady-state transitional boundary layer at the downstream station. The velocity defect in the passing wake changes the local pressure at the leading of the airfoil, significantly affects the time-mean pressure distribution on the airfoil and eventually, has influence on the transition process of the boundary layer.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.233-240
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• 2024

The wall friction correlations of oscillatory natural circulation loops are highly loop-specific, making it difficult to perform 1-D system simulations before obtaining specific experimental data. To better predict the friction characteristics, the nonlinear dynamics of a toroidal single-phase natural circulation loop were numerically investigated, and the transition effect was considered. The k-k_L-ω transitional turbulence and k-ω SST turbulence models were used to compute the flow characteristics of the loop under different heating powers varying from 0.48 to 1.0 W/cm², and the results of both models were compared with previous experiments. The mass flow rates and friction factors predicted by the k-k_L-ω model showed a better agreement with the experimental data than the results of the k-ω SST model. The oscillation frequencies calculated using both models agreed well with the experimental data. The k-k_L-ω transitional turbulence model provided better friction-factor predictions in oscillatory natural circulation loops because it can reproduce the temporal and spatial variation of the wall shear stress more accurately by capturing the movement of laminar, transition turbulent zones inside unstable natural circulation loops. This study shows that transition effects are a possible explanation for the highly loop-specific friction correlations observed in various oscillatory natural circulation loops.

• 동력기계공학회지
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• 제4권3호
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• pp.40-47
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• 2000

The turbulent flow with wake, reattachment and recirculation flow is very important from the viewpoint of engineering. But that is still difficult because of especially the unsteady problems which are related with the vehicle dynamics and the aerodynamics noise. This paper evaluate LES that can analyze about all fluid flow region including the laminar, transition and turbulent. So we compare the results of LES with those of PIV measurement and Reynolds averaging models. In conclusion, LES predicts flow behavior better than Reynolds averaging models.

• 한국산업융합학회 논문집
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• 제11권1호
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• pp.19-26
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• 2008

The gas-liquid mass transfer volumetric coefficients in gas-liquid agitated vessels with wire gauge impellers were measured to be compared with those in vessels with disk turbine and paddle impellers. Also mass transfer volumetric coefficients for disk turbine, paddle impeller and wire gauge impeller in cylindrical agitated vessel was measured over a wide range of Reynolds number from turbulent flow to transition regions. The effect of geometries on $k_La$ is clarified experimentally. Mass transfer volumetric coefficients $k_La$ depends only on the power consumption ($P_{gv}+P_{av}$) per unit volume.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 추계학술대회 논문집 학회본부 C
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• pp.1061-1064
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• 1998

To examine the influence of unsteady wake on the flow and heat transfer characteristics, an experiment has been conducted in a four-vane linear cascade. Flow and heat transfer measurements are made for the inlet Reynolds number of 66000(based on chord length and free-stream velocity). Turbulent intensity and stress were measured using hot wire anemometer, and to measure the convective heat transfer coefficients on the blade surfaces liquid crystal/gold film Intrex technique was used. The disturbance by the unsteady wake is characterized by the unresolved unsteadiness. The unsteady wake enhances the turbulent motion of flow in the cascade passage. It also promotes the boundary layer development and transition. The results show that heat transfer coefficients on the suction surface increase with increasing unresolved unsteadiness.

• 한국전산유체공학회지
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• 제18권4호
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• pp.47-52
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• 2013

In the present study, the turbulent flow from an annular jet is investigated by using large eddy simulation. Particularly, the effect of the ratio of the inner and outer diameters is one of the main interests of this study. The instantaneous fields presented in this paper showed that behind the jet exit the backflow region, as well known in literatures, exists, and its detailed behavior depends on the ratio of the inner and outer diameters ($D_1/D_2$). The dependence on $D_1/D_2$ is attributed to the different shear layer development according to $D_1/D_2$. At small $D_1/D_2$, the development of the outer shear layer is similar to that from the circular jet. However, with increasing $D_1/D_2$, the interaction between the outer and inner shear layers becomes strong, resulting in fast transition to turbulence.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.250-257
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• 2005

Large eddy simulation{LES) methodology used to model a bluff-body stabilized non-reacting flow. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code, the results was compared with that of Reynolds Averaged Navier-Stokes(RANS) using $k-{\epsilon}$ model as well as experimental data. The results showed that the LES and RANS qualitatively well predicted the experimental results, such as mean axial, radial velocities and turbulent kinetic energy. However, in the quantitative analysis, the LES showed a better prediction performance than RANS. Specially, the LES well described characteristics of the recirculation zones, such as air stagnation point and jet stagnation point. Finally, the unsteady phenomena on the Bluff-body, such as the transition of recirculation region and vorticity, was examined with LES methodology.