• 산업기술연구
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• 제23권A호
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• pp.9-13
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• 2003

Numerical experiments are done by a commercial code, PHOENICS to evaluate the backlayer phenomenon of smoke in case of the road tunnel fire. The independent and dependent variables are ventilation air velocity and the length of backlayer of smoke respectively. Hybrid scheme and ${\kappa}-{\varepsilon}$ turbulence model are adopted in the simulation process and mass residual is used as a convergence criterion. The experimental results say that the length of backlayer is reduced with the increase of ventilating air velocity and that there is a critical air velocity which prevents from the onset of backlayering phenomena. One finds that there is a fresh air region near the bottom of tunnel which could make the passenger escape safely from the polluted region by smoke. These phenomena come from the vertical stratification of the smoke air mixture in the tunnel.

• 한국해안해양공학회지
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• 제17권2호
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• pp.86-97
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• 2005

파랑하중하의 지반내 간극수압의 정확한 평가는 연안구조물에서 지반의 안정성을 검토하는데 중요한 요소이다. 파$\cdot$구조물 지반의 상호간섭에 대한 대부분의 기존 수치모델은 파동장과 지반부를 분리하여 해석하는 Hybrid기법을 적용하고 있기 때문에, 보다 고정도로 이들의 상호간섭을 모의하기 위해서는 파랑하중하에서 파$\cdot$구조물$\cdot$지반을 일체화한 수치모델의 개발이 필요하다. 본 연구에서는 투과층의 다양한 기하학적인 형태에 따라 층류저항까지 고려한 모델화 된 유체저항을 도입하여 파 구조물 지반의 비선형동적응답을 해석하기 위한 직접수치해석기법을 새롭게 제안하였다 직접수치해석기법은 Hybrid기법과는 달리 유체와 다공질매체의 접합면에서 특별한 경계조건을 필요로 하지 않는다. 파$\cdot$구조물$\cdot$지반의 상호간섭에 대해 기존의 수리실험결과와 본 연구의 계산결과를 비교함으로써 좋은 일치성을 확인할 수 있었다. 따라서 새롭게 제안된 본 수치기법은 파 구조물 지반의 비선형동적응답을 평가하는 유용한 기법으로 판단된다.

• 한국소음진동공학회논문집
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• 제21권12호
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• pp.1138-1145
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• 2011

The internal broadband noise of a centrifugal fan in a household refrigerator is predicted using hybrid CAA techniques based on stochastic turbulent synthetic model. First, the unsteady flow field around the centrifugal fan is predicted using computational fluid dynamics(CFD) method. Then, the turbulent flow field is synthesized by applying the stochastic turbulent synthetic technique to the predicted flow field. The aerodynamic noise sources of the centrifugal fan are modeled on a basis of the synthesized turbulent field. Finally, the internal broadband noise of the centrifugal fan is predicted using the boundary element method(BEM) and the modeled sources. The predicted noise spectrum is compared with the experimental data. It is found that the predicted result closely follows the experimental data. The proposed method can be used as an effective tool for designing low-noise fans without expensive computational cost required generally for the LES and DNS simulations to resolve the turbulence flow field responsible for the broadband noise.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.627-632
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• 2011

The internal broadband noise of a centrifugal fan in a household refrigerator is predicted by using hybrid CAA technique based on stochastic turbulent synthetic model. First, the unsteady flow field around the centrifugal fan is predicted using Computational Fluid Dynamics (CFD) method. Then, the turbulent flow field is synthesized by applying the stochastic turbulent synthetic technique to the predicted flow field. The aerodynamic noise sources of the centrifugal fan are modeled on a basis of the synthesized turbulent field. Finally, the broadband noise of the centrifugal fan is predicted using Boundary Element Method (BEM) and the modeled sources. The predicted result is compared with the experimental data. It is found that the predicted result closely follows the experimental data. The proposed method can be used as an effective tool for designing low-noise fans without expensive computational cost required generally for the LES and DNS simulations to resolve the turbulence flow field responsible for the broadband noise.

• 대한기계학회논문집B
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• 제32권6호
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• pp.471-478
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• 2008

Detached Eddy Simulation (DES) is performed for developing turbulent flow of the $270^{\circ}$ curved duct at a Reynolds number of 56,690. The curvature ratio on the basis of a centric radius $R_c$ and a duct height H is 3.357. Turbulence models adopted are k-$\omega$ model for Reynolds Average Navier-Stokes (RANS) equation Simulation and Shear Stress Transport (SST) model for DES. DES is used as the hybrid computation technique combined with RANS-SST and Large Eddy Simulation (LES). Predicted results are compared with measured results including the distributions of Reynolds stresses and the flow characteristics on the symmetric plane of curved duct are presented. Judging from the comparison between the predicted and the measured results, the DES approach is applicable to calculate the developing turbulent flow in a $270^{\circ}$ curved duct.

• 국제초고층학회논문집
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• 제11권4호
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• pp.287-300
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• 2022

Unconventional structures are getting more popular in recent days. Large-span roofs are used for many structures, such as airports, stadiums, and conventional halls. Identifying the pressure distribution and wind load acting on those structures is essential. This paper offers a collaborative study of computational fluid dynamics (CFD) simulations and wind tunnel tests for assessing wind pressure distribution for a building with a combined slender curved roof. The hybrid turbulence model, Improved Delayed Detached Eddy Simulation (IDDES), simulates the open terrain turbulent flow field. The wind-induced local pressure coefficients on complex roof structures and the turbulent flow field around the structure were thus calculated based upon open terrain wind flow simulated with the FLUENT software. Local pressure measurements were investigated in a boundary layer wind tunnel simultaneous to the simulation to determine the pressure coefficient distributions. The results predicted by CFD were found to be consistent with the wind tunnel test results. The comparative study validated that the recommended IDDES model and the vortex method associated with CFD simulation are suitable tools for structural engineers to evaluate wind effects on long-span complex roofs and plan irregular buildings during the design stage.

• 에너지공학
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• 제22권4호
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• pp.399-405
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• 2013

엔진 실린더 내부의 난류유동 특성은 내연기관의 열효율을 결정하는 매우 중요한 역할을 한다. 실린더 내 난류유동은 복잡한 3차원 유동으로 유동특성에 대한 자세한 정보는 엔진설계의 최적화를 위해 필수적이다. 균일 예혼합 압축착화(HCCI) 엔진은 가솔린과 디젤엔진 사이의 하이브리드 연소개념이다. 실린더 내 기체의 난류유동은 운동량과 열의 혼합 및 전달률을 증가시키므로 벽면에서의 열전달에 관여하여 HCCI 연소 과정에 중요한 영향을 미치게 된다. 본 연구에서는 연소실 형상에 따른 연소실 내의 기체 난류유동을 LES 모델을 사용한 전산수치해석을 통해 분석하여 HCCI 엔진 연소과정에 미치는 영향을 확인하였고 연구결과는 HCCI 엔진에서 연소실 형상에 따른 연소 특성과 엔진 성능을 개선하기 위한 기본적인 지침에 활용될 수 있다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2020년도 학술발표회
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• pp.149-149
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• 2020

하천에서 물 흐름이 보와 댐과 같은 수공구조물을 지날 때 일반적으로 흐름상태에 다양하고 급진적인 변화가 발생한다. 특히 흐름이 구조물을 지나면서 사류(supercritical flow)로 변하고 다시 상류(subcritical flow)로 복원되면서 일어나는 도수(hydraulic jump) 현상은 수위의 급변화, 흐름 에너지 소산, 변동성이 강한 압력 분포 등이 특징이다. 이러한 흐름 특성들은 보나 여수로와 같은 수공구조물 자체의 성능뿐만 아니라 이들 수공구조물의 하류에서 발생하는 국부세굴로 인해 구조물의 안정성에 부정적인 영향을 줄 수 있다. 따라서 수공구조물을 설계할 때는 이들 구조물을 통과하는 흐름의 비정상 난류 흐름 특성을 정확하게 해석하여 반영하여야 한다. 이 연구에서는 k-omega SST 난류 모형과 자유수면의 급격한 변동을 해석하기 위한 하이브리드-VOF(hybrid volume of fluid)기법을 이용하여 도수현상을 수치적으로 재현하고자 한다. 기존 CFD(computational fluid Dynamics) 모델링에서는 자유수면 변동의 영향을 고려하기 위해 VOF 기법을 많이 사용하였다. 하지면 전통적인 VOF 기법은 다상흐름(multiphase flow)을 오직 부피분율(volume fraction)의 함수로만 고려하며 모의함으로써 강한 수면변동뿐만 아니라 공기연행(air entrainment)를 동반하는 난류 흐름을 모의하는데는 한계가 있다. 이 연구에서 이용하는 Eulerian 기법인 하이브리드 VOF 기법은 물과 공기의 각 상에 대하여 흐름 특성들을 개별적으로 계산하기 때문에 공기연행을 포함한 급변류 흐름에서 전통적인 VOF 기법보다 적용성이 우수하다. 이와 같은 난류모형과 자유수면 포착기법을 이용하여 3차원 비정상 난류 흐름 수치모형을 구축하여 수공구조물 주변에서 발생하는 강한 공기연행과 난류 특성를 보이는 급변류를 수치적으로 재현한다. 이 연구는 계산된 수치해석 결과를 기존 수리실험 결과와 비교하여 수치모형의 적용성을 평가하고 도수 현상에서 발생하는 독특한 흐름 특성을 제시한다.

• The Journal of the Acoustical Society of Korea
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• 제22권4E호
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• pp.183-196
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• 2003

General algorithm is developed for the prediction of internal flow-induced noise. This algorithm is based on the integral formula derived by using the General Green Function, Lighthill's acoustic analogy and Curl's extension of Lighthill's. Novel approach of this algorithm is that the integral formula is so arranged as to predict frequency-domain acoustic signal at any location in a duct by using unsteady flow data in space and time, which can be provided by the Computational Fluid Dynamics Techniques. This semi-analytic model is applied to the prediction of internal aerodynamic noise from a throttle valve in an automotive engine. The predicted noise levels from the throttle valve are compared with actual measurements. This illustrative computation shows that the current method penn its generalized predictions of flow noise generated by bluff bodies and turbulence in flow ducts.

• Wind and Structures
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• 제29권2호
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• pp.111-127
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• 2019

The tapered and set-back type of unconventional designs have been used earlier in many buildings. These shapes are aerodynamically efficient and offer a significant amount of damping against wind-induced forces and excitations. Various studies have been conducted on these shapes earlier. The present study adopts a hybrid approach of turbulence modelling i.e., Detached-eddy Simulation (DES) to investigate the effect of height modified tapered and set-back buildings on aerodynamic forces and their sensitivity towards pressure. The modifications in the flow field around the building models are also investigated and discussed. Three tapering ratios (T.R.=(Bottom width- Top width)/Height) i.e., 5%, 10%, 15% are considered for tapered and set-back buildings. The results show that, mean and RMS along-wind and across-wind forces are reduced significantly for the aerodynamically modified buildings. The extent of reduction in the forces increases as the taper ratio is increased, however, the set-back modifications are more worthwhile than tapered showing greater reduction in the forces. The pressure distribution on the surfaces of the buildings are analyzed and in the last section, the influence of the flow field on the forces is discussed.