• 한국전산유체공학회지
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• 제15권2호
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• pp.71-78
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• 2010

As a step toward accurate prediction of droplet impingement and ice accretion on aircraft, an Eulerian-based droplet impingement and ice accretion code for air flows around an airfoil containing water droplets is developed. A CFD solver based on the finite volume method was also developed to solve the clean airflow. The finite-volume-based approach for simulating droplet impingement on an airfoil was employed owing to its compatibility with the CFD solver and robustness. For ice accretion module, a simple model based on the control volume is combined with the droplet impingement module that provides the collection efficiency. To validate the present code, it is compared with NASA Glenn IRT (Icing Research Tunnel) experimental data and other well-known icing codes such as LEWICE and FENSAP-ICE. It is shown that the collection efficiency and shape of ice accretion are in good agreement with previous experimental and simulation results.

• 한국분무공학회지
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• 제2권1호
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• pp.36-45
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• 1997

A spray-wall impingement model for fuel sprays is proposed and implemented as a module into the KIVA-POSTECH code. The model is based on the single droplet experiments. The droplet behaviors after impingement are determined from experimental correlations. Different behaviors of impinged droplets depend on the wall temperature and the critical temperature of the fuel. Fuel film formation is taken into account so that the model can be applicable to any wall temperature and injection conditions. Computational results on a normal and on inclined wall are in good agreement for the spray shape and penetration. More validation against experiments and development of the heat transfer model are needed for further improvement.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1183-1192
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• 2001

The numerical simulation has been conducted for the investigation of flow and heat transfer characteristics of an oblique impingement jet injected to a flat plate. The finite volume method was used to discretize the governing equations based on the non-orthogonal coordinate with non-staggered variable arrangement. The $textsc{k}$-$\varepsilon$-ν(sup)'2 turbulence model was employed to consider the consider the anisotropic flow characteristics generated by the impingement jet flow. The predicted results were compared with the experimental data and those of the standard $textsc{k}$-$\varepsilon$ turbulence model. The results of the $textsc{k}$-$\varepsilon$-ν(sup)'2 model showed better agreement with the experimental data than those of the standard $textsc{k}$-$\varepsilon$ model. In order to get the optimum condition, the flow and temperature fields were calculated with a variation of inclined angle($\alpha$=30$^{\circ}$~90$^{\circ}$) and the distance between the jet exit and impingement plate-to-diameter (L/D=4~10) at a fixed Reynolds number(Re=20,000). For a small L/D, the near-peak Nusselt numbers were not significantly effected by the inclined angle. The near-peak Nusselt numbers were not significantly affected by the L/D in the case of a large $\alpha$. The overall shape of the local Nusselt numbers was influenced by both the jet orifice-to-plate spacing and the jet angle.

• 한국시뮬레이션학회논문지
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• 제14권2호
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• pp.35-43
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• 2005

Feedwater heaters of many nuclear power plants have recently experienced wall thinning damage, which will increase as operating time progresses. As it is judged that the wall thinning damages have generated due to local fluid behavior around the impingement baffle installed in downstream of the high pressure turbine extraction steam line to avoid colliding directly with the tubes, numerical analyses using PHOENICS code were performed for two models with original clogged impingement baffle and modified multi-hole impingement baffle. To identify the relation between wall thinning and fluid behavior, the local velocity components in x-, y-, and z-directions based on the numerical analysis for the model with the clogged impingement baffle were compared with the wall thickness data by ultrasonic test. From the comparison of the numerical analysis results and the wall thickness data, the local velocity component only in the y-direction, and not in the x- and z-direction, was analogous to the wall thinning configuration. From the result of the numerical analysis for the modified impingement baffle to mitigate the shell wall thinning, it was identified that the shell wall thinning may be controlled by the reduction of the local velocity in the y-direction.

• Journal of Mechanical Science and Technology
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• 제15권3호
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• pp.374-383
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• 2001

The spray/wall interaction is considered as an important phenomenon influencing air-fuel mixing in the internal combustion engines. In order to adequately represent the spray/wall interaction process, impingement regimes and post-impingement behavior have been modeled using experimental data and conservation constraints. The modeled regimes were stick, rebound, spread and splash. The tangential velocities of splashing droplets were obtained using a theoretical relationship. The continuous phase was modeled using the Eulerian conservation equations, and the dispersed phase was calculated using a discrete droplet model. The numerical simulations were compared to experimental results for spray impingement normal to the wall. The predictions for the secondary droplet velocities and droplet sizes were in good agreement with the experimental data.

• 한국자동차공학회논문집
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• 제10권5호
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• pp.45-57
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• 2002

In this paper, the results gained by applying many impingement models to the cylinder and flat plate were analyzed in comparison with the experimental data to study a spray/wall interaction phenomena. To begin with, the behavior of spray injected normal to the wall was analysed using three different impingement models ; Naber and Reitz model(NR model), Watkins and Wang model(WW model) and Park and Watkins model(PW model) in the present calculation. The results obtained from these models were compared with experimental data of Katsura et. al. The results indicated that PW model was in better agreement with experimental data than the NR and WW model. Also f3r spray injected at 30DEG , the result of three models were compared with experimental data of Fujimoto et. al. The results showed that m model overpredicted the penetration in the radial direction because this model was based on the inviscid jet analogy. WW model did not predicted the radius and height of the wall spray effectively. It might be thought that this discrepancy was due to the lack of consideration of spray film velocity occurred at impingement site. The result of PW model agrees with the experimental data as time goes on. In particular, a height of the spray droplets was predicted more closely to the experimental data than the other two models. The results of PW model in which the spray droplets were distributed densely around the edge of droplet distribution shaped in a circle had an agreement with the experimental data of Fujimoto et. al. Therefore, it was concluded that PW model performed better than M and WW model for prediction of spray behavior. The numerical calculation using PW model performed to the cylinder similar to the real shape of DI engine. The results showed that vortex strength near the wall in the cylinder was stronger than that in the case of flat plate. Contrary to the flat plat, an existence of the side wall in the cylinder caused the tangential velocity component to be reduced and the normal velocity component to be increased. The flow tends to rotate to the inside of cylinder going upward to the right side wall of cylinder gradually as time passes. Also, the results showed that as the spray angle increases, the gas velocity distribution and the tumble flow seemed to be formed widely.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.71-74
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• 2008

NUFLEX is a general purpose thermo/fluid flow analysis program which has various physical models including spray. In NUFLEX, spray models are composed of breakup and collision models of droplet. However, in case of diesel engine, interaction between wall-film and impingement model considering heat transfer is not coded in NUFLEX. In this study, Lee & Ryou impingement & wall-film model considering heat transfer is applied to NUFLEX. For the verification of this NUFLEX program, numerical results are compared with experimental data. Differences of film thickness and radius between numerical results and experimental data are within 10% error range. The results show that NUFLEX can be used for comprehensive analysis of spray phenomena.

• 한국금형공학회:학술대회논문집
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• 한국금형공학회 2008년도 하계 학술대회
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• pp.135-139
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• 2008

Development of surface heating technology using hot jet impingement onto mold inner surface for improvement of pattern transcription. This study is focused on how to control the parameters related to hot jet impingement. The mass flow rate, the jet temperature and the duration of the impingement are major parameters. The nozzle design and other geometric configurations also affect the heat transfer to the surface. In terms of heat transfer analysis, the most important number is the heat transfer coefficient, which is influenced by the mass flow rate, nozzle design, distance between the nozzle tip and the surface. In summary, several parametric studies using the developed model are conducted to investigate the effects of mass flow rate, jet temperature and Heating Time in Surface heating technology using hot jet impingement onto mold.

• 한국항공우주학회지
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• 제40권8호
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• pp.647-654
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• 2012

외부 환경조건에 의한 항공기 위협인자로서 과냉각 대형 액적은 그 중요성이 지속적으로 보고되고 있다. 이러한 대형 액적의 거동은 상대적으로 작은 액적과 달리 그 형태가 변화하며 액적이 표면과 충돌시 파편이 발생하는 등 다양한 물리적 특성을 나타낸다. 이러한 대형 액적의 거동을 시뮬레이션 하기 위해 비정렬 격자계 기반 2차원 압축성 Navier-Stokes 코드와 액적 거동 시뮬레이션 코드를 개발하였다. 또한 대형 액적의 물리적 현상을 모사하기 위해 반경험적 기법에 기반한 액적항력모델과 액적-고체표면 충돌 모델을 기존 액적장 지배방정식의 액적항력계수 및 경계면의 수치적 경계조건으로 적용하였다. 그 결과 풍동 시험과 액적충돌 영역 및 최대 축적율은 매우 유사하게 나타난 반면 NACA23012 익형의 아랫면 주위 축적율의 경향은 풍동 시험보다 다소 크게 나타났다.

• 대한기계학회논문집B
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• 제41권5호
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• pp.329-339
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• 2017

충돌제트는 제트가 충돌하는 정체 영역에 매우 높은 열전달을 제공하기 때문에 다양한 분야에서 적용되고 있다. 그러나 제트가 벽면에 부딪친 후 벽면 제트에 의해 야기되는 충돌 챔버 내의 횡방향 유동은 여러 개의 제트로 구성된 배열제트인 경우 하류에 있는 제트 유동을 방해하거나 휘게 할 수 있으며, 이로 인해 배열 충돌제트의 냉각 성능은 감소하게 된다. 파형 구조는 하류 제트에서의 횡방향 유동영향을 줄이기 위해 인접한 충돌 제트 사이에 있는 파형 속에 사용된 냉각 공기를 유입시키는 역할을 하며, 이러한 파형 구조에서의 유동 및 열전달 특성에 대해 수치해석을 수행하였다. 3차원, 정상상태, 비압축성 유동으로 고려하고 해석하였으며 ANSYS-CFX 15.0 코드를 사용하였다. 파형 구조의 형상 변수가 배열 충돌제트의 횡방향 유동 억제에 미치는 영향을 제시하고 분석하였다.