CFD모델과 풍동실험을 이용한 복잡지형에서의 기류해석

문기영,김석철,신구용,조경학,윤정임,황규석,길용식 한국풍공학회 2009 한국풍공학회지 Vol.13 No.3

Winds over a complex terrain were analyzed using wind tunnel and several computational fluid dynamics (CFD) models. A mountain area adjacent to a shoreline was chosen in a Southern Korea Peninsula for study. Two different CFD models were used for simulating flows: one is an FVM code with Virtual Boundary Method(VBM) using LES for sub-grid turbulence, and the other is a commercial package implemented with 4 different RANS (Reynolds Averaged Navier-Stokes Equations) turbulence models. The CFD simulations were compared with wind tunnel data at several locations where wind speeds were greatly enhanced or reduced due to the surrounding topographic features. The agreement between the CFD simulations and the wind tunnel experiments were good, the correlation coefficients ranging 0.890 ~ 0.965. The FVM code was excellent of which correlation coefficient was 0.965. 자연지형에 의한 기류 변화를 CFD 모델과 풍동실험을 통하여 비교 연구하였다. 해안에 인접한 남부 산악지형을 대상으로 풍동실험과 몇 종류의 CFD 모델 시뮬레이션을 수행하였다. 사용한 CFD 모델은 2 가지로, 하나는 LES 난류모델을 사용하는 가상경계기법을 활용한 유한체적법(Finite Volume Method, FVM) 코드와 또 하나는 4 가지 RANS 난류모델이 선택사양으로 제공되는 상업용 CFD 모델이다. 지형에 의해 풍속이 증가되는 지점과 감소되는 지점에서 수직풍속분포를 직접 비교하고 상관도를 구하였다. CFD 모델과 풍동실험과의 상관도()는 0.890 ~ 0.965로 매우 높게 나타났으며, CFD 모델 중 VBM LES CFD 모델은 상관도 0.965로 나타나 풍동실험을 가장 잘 모사하는 것으로 분석되었다.

전산 유체 역학 모델을 이용한 도시지역 흐름 및 열 환경 수치모의 검증

김도형,김근회,변재영,김백조,김재진 한국지구과학회 2017 한국지구과학회지 Vol.38 No.7

The purpose of this study is to verify urban flow and thermal environment by using the simulated Computational Fluid Dynamics (CFD) model in the area of Gangnam Seonjeongneung, and then to compare the CFD model simulation results with that of Seonjeongneung-monitoring networks observation data. The CFD model is developed through the collaborative research project between National Institute of Meteorological Sciences and Seoul National University (CFD_NIMR_SNU). The CFD_NIMR_SNU model is simulated using Korea Meteorological Administration (KMA) Local Data Assimilation Prediction System (LDAPS) wind and potential temperature as initial and boundary conditions from August 4-6, 2015, and that is improved to consider vegetation effect and surface temperature. It is noticed that the Root Mean Square Error (RMSE) of wind speed decreases from 1.06 to 0.62 m s−1 by vegetation effect over the Seonjeongneung area. Although the wind speed is overestimated, RMSE of wind speed decreased in the CFD_NIMR_SNU than LDAPS. The temperature forecast tends to underestimate in the LDAPS, while it is improved by CFD_NIMR_SNU. This study shows that the CFD model can provide detailed and accurate thermal and urban area flow information over the complex urban region. It will contribute to analyze urban environment and planning. 이 연구의 목적은 강남 선정릉지역에서 전산유체역학모델(CFD)을 사용하여 도시지역의 흐름 및 열 환경 모의를검증하는 것이고, CFD 모델의 모의결과와 선정릉 지역의 관측 자료와 비교하는 것이다. CFD 모델은 국립기상과학원과서울대가 공동으로 연구 개발된 모델이다. CFD_NIMR_SNU 모델은 기상청 현업 모델인 국지예보모델(LDAPS)의 바람성분과 온도성분을 초기 및 경계조건으로 적용되었고 수목효과와 지표 온도를 고려하여 2015년 8월 4일에서 6일까지강남 선정릉 지역을 대상으로 수치실험을 진행하였다. 선정릉지역에서 수목효과 적용 전후의 풍속을 비교하였을 때 평균 제곱근 오차(RMSE)는 각각 1.06, 0.62 m s−1로 나타났고 수목효과 적용으로 풍속 모의정확도가 향상되었다. 기온은 LDAPS 과소 모의하는 경향을 나타내고 CFD_NIMR_SNU 모델에 의해 향상된 것을 확인하였다. CFD_NIMR_SNU 모델을 이용하여 복잡한 도시지역의 흐름과 열 환경을 자세하고 정밀한 분석이 가능하며, 도시 환경 및 계획에 대한 정보를 제공 할 수 있을 것이다.

CFD해석을 이용한 축류형 혈액펌프의 용혈평가 및 형상개량에 관한 기초연구

김동욱,임상필 대한의용생체공학회 2004 의공학회지 Vol.25 No.1

The non pulsation blood pump is divided into axial flow and centrifugal style according to the direction of inlet and outlet flow. An axial flow blood pump can be made smaller than a centrifugal blood pump because centrifugal pump's rpm is fewer than axial flow pump. Hemolysis is an important factor for the development of an axial flow blood pump. It is difficult to identify the areas where hemolysis occurs. Evaluation of hemolysis both in in-vitro and in-vivo test requires a long-time and more expensive. Computational fluid dynamics(CFD) analysis enables the engineer to predict hemolysis on a computer which just can get not only amount of htmolysis but also location of hemolysis. It takes shorter time and less expensive than in-vitro test. The purpose of this study is to git Computational fluid dynamics in axial flow pump and to verify the accuracy of prediction by the possibility of design comparing CFD results with in-vitro experimental results. Also, wish to figure out the correction method that can bring improvement in shape of axial flow blood pump using CFD analysis. 최근 심장질환에 의한 사망자 수는 놀랄 만큼 빠른 증가세를 보이고 있다. 인공심장은 혈액의 흐름에 따라 크게 박동류형과 무박동류형으로 나뉘며, 무박동류형 펌프는 비용적형으로 박동류형에 비해 소형화가 가능하다는 장점을 가지고 있다. 이러한 무박동류형 혈액펌프는 다시 구동방식에 따라 축류형과 원심형으로 구분되어지며, 그중 축류형 혈액펌프는 같은 무박동류형인 원심형 혈액펌프와 비교하였을 때 훨씬 간단한 구동장치와 제어장치를 가진다. 혈구가 파괴되어 헤모글로빈이 혈구 밖으로 빠져나가는 것을 용혈이라 하며 혈액이 응고하여 혈관을 막게되는 혈전현상은 이러한 용혈이 주된 원인이다. 따라서 혈액펌프가 구동함에 따라 발생하게 되는 용혈의 수치를 낮추는 것은 혈액펌프를 개발하는데 있어서 중요한 조건 중에 하나이다 이러한 용혈을 평가하기 위한 방법으로는 현재 in-vitro실험이 가장 널리 사용되어지고 있으나, 이러한 체외실험을 하기 위해선 상당한 비용과 장기간의 연구기간이 요구되어진다. 이러한 in-vitro실험의 단 전을 보완하기 위해 개발되어진 CFD해석법은, 엔지니어로 하여금 in-vitro실험을 실시하지 않고 용혈이 발생하는 지역과 용혈발생예측치를 추정할 수 있다. 본 연구의 목적은 in-vitro실험의 결과데이터와 CFD해석의 예측결과데이터의 여러 가지 비교를 통해 CFD해석의 정확성을 검증하고, 또한 이러한 정확성이 검증된 CFD해석법을 현재 개발되어지고 있는 축류형 혈액펌프의 개발단계에 적용하기 위함이다.

CFD/DSMC 혼합해석기법을 이용한 축대칭 천이영역 유동 해석

최영재(Young-Jae Choi),권오준(Oh-Joon Kwon) 한국항공우주학회 2019 韓國航空宇宙學會誌 Vol.47 No.3

본 연구에서는 희박기체 환경의 유동 정보를 효과적으로 계산하기 위해 CFD 해석기법과 DSMC 해석기법 간 연계 해석을 수행하는 CFD/DSMC 혼합해석기법을 개발하였으며, 개발된 해석기법을 이용하여 천이영역에서의 고속 비행체 주위 유동에 대한 해석을 수행하였다. 해석 형상으로는 콘과 실린더 형태로 이루어진 FRESH-FX 형상으로 고려하였고, 혼합해석기법의 결과는 순수 CFD 및 DSMC 해석 결과와 비교하였다. 천이영역의 대기가 상대적으로 희박하여 초음속 유동에서 발생하는 충격파의 구배 및 세기가 약화된 것을 확인하였다. 순수 CFD 해석 결과와는 차이를 보였고, 순수 DSMC 해석 결과와 거의 일치하는 결과를 도출하는 것을 확인하였다. 또한, 순수 DSMC 계산시간보다 해석 시간이 감소하였다. 이를 통해 혼합해석기법의 결과에 대한 신뢰성 및 해석 시간에서의 효율을 확인하였다. In the present study, a CFD/DSMC hybrid method performed by a coupled analysis between the CFD method and the DSMC method was developed to obtain the flow information on the rarefied gas flows effectively. Flow simulations around the high speed vehicles on the transition flow regimes were conducted by using the developed method. The FRESH-FX vehicle made of cone and cylinder shapes was considered for the simulations. The results of the hybrid method were compared with the results of the pure CFD and the pure DSMC method to confirm the reliability and efficiency of the hybrid method. It was found that the gradient and the intensity of the shock waves were weakened due to the relatively low density on the transition flow regime. It was confirmed that the results of the hybrid analysis were different to those of the pure CFD analysis and almost identical to those of the pure DSMC analysis. In addition, the computational time of the hybrid method was reduced than that of the pure DSMC method. As a result, it was obtained that the validity and the efficiency of the CFD/DSMC hybrid method.

CFD 시뮬레이션 시 디퓨져 유형에 따른 모델링 및 해석 방법에 관한 연구

석호태(Seok Ho-Tae),최동호(Choi Dong-Ho),김호진(Kim Ho-Jin),양정훈(Yang Jeong-Hoon) 대한건축학회 2010 대한건축학회논문집 Vol.26 No.1

Because people spend most of their time indoors nowadays, various technical systems are required to efficiently maintain comfortable indoor temperatures. Diffusers play an important role in air conditioners; therefore, the selection of the diffuser is crucial to the efficiency of the air conditioner. Currently, predictive assessments of the ideal indoor thermal environment are made using CFD(Computational Fluid Dynamics); however, the CFD method rarely carefully considers the importance of diffusers. Diffusers affect the result of the air flow and distribution of heating and cooling, so we must carefully consider diffusers in CFD. With more accurate CFD models of diffusers, the energy load can more efficiently be predicted in the architectural design step. To keep adequate IAQ(Indoor Air Quality), a result of restriction of excessive air flow and preferable limitation to the occupancy zone, the air flow pattern should be projected and adjusted as well. Among numerical analysis models, the CFD model is currently being used to predict air flow distribution. However, various results of the CFD analysis method have caused some errors, proving that a more accurate calculation method is required. The purpose of this study is to suggest the CFD calculation method to simulate diffusers in order to minimize the errors between results of the predicted energy performance and ventilation efficiency and the actual physical condition.

Multi-scale computational fluid dynamics of impregnation die for thermoplastic carbon fiber prepreg production

Ngo, Son Ich,Lim, Young-Il,Hahn, Moon-Heui,Jung, Jaeho,Bang, Yun-Hyuk Elsevier 2017 Computers & chemical engineering Vol.103 No.-

<P><B>Abstract</B></P> <P>A multi-scale computational fluid dynamics (CFD) model of a pultrusion process was proposed for unidirectional carbon fiber (UD-CF) prepreg production. Polyamide 6 (PA6) and polyacrylonitrile-based CF were used as the thermoplastic polymer matrix and reinforcement, respectively. The non-Newtonian viscosity of PA6 was expressed by Carreau's model. A micro-scale CFD model was constructed to obtain a proper resin permeability to CF filaments, while the tow domain was treated as sliding porous media in the macro-scale CFD. The resin velocity profile showed a similar shape to the relative resin amount experimentally measured in the UD-CF prepreg. The uniformity index of the resin velocity (<I>UI</I> <SUB> <I>v</I> </SUB>) on the outlet surface was calculated for 45 case studies with several tow speeds and resin flow rates. The tow speed showing a maximum <I>UI</I> <SUB> <I>v</I> </SUB> was remarkably well expressed as a linear function of the slip velocity, which is the difference between the tow speed and resin velocity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A multi-scale CFD model was developed for a carbon fiber (CF) impregnation process. </LI> <LI> Resin permeability to CF filaments was obtained from a micro-scale CFD model. </LI> <LI> Uniformity index (<I>UI</I>) of the resin velocity was obtained from a macro-scale CFD model. </LI> <LI> Tow speed showing maximum <I>UI</I> was expressed as a linear function of the slip velocity. </LI> </UL> </P>

전산유체해석을 통한 고층 건물의 풍압계수 산정

김민규,강현구 한국풍공학회 2020 한국풍공학회지 Vol.24 No.3

Recently, Architectural Institute of Japan (AIJ 2015) allowed using CFD analysis for the calculation of wind loads. Thismeans that computer based analysis has reached to similar level with the wind tunnel test due to the improvement of the computingpower and CFD analysis theory. This study first dealt with the theoretical background of CFD analysis and conducted the analysisbased on the AIJ guideline and the recommendation by the European Cooperation in Science and Technology (COST). Wind tunneltest data provided by Tokyo Polytechnic University were used to verify the reliability of the analysis results. Wind loads with aspectratios of 3, 4 and 5 were compared to assess the similarity between the analysis results and the wind tunnel test data. 최근 일본의 건축구조기준(AIJ 2015)에서는 CFD 해석을 통한 풍하중 산정을 허용한 바 있다. 이는 컴퓨터의 연산 능력 향상및 CFD 해석 이론의 발전으로 인해 해석의 결과가 풍동실험의 결과와 유사한 수준에 도달하였음을 뜻한다. 본 연구에서는 먼저 CFD해석의 이론적 배경을 살펴보고, 일본의 건축구조기준 및 유럽의 과학기술연구 프로그램인 COST에서 권장한 CFD 해석 절차를 토대로 해석을 진행하였다. 해석 결과의 신뢰성을 검증하기 위해 Tokyo Polytechnic University에서 제공하는 풍동실험 데이터를 사용하였고, 해석과 실험의 유사성을 평가하기 위하여 형상비가 3, 4, 5일 때의 풍방향하중을 비교하였다.

CFD를 이용한 가연성 가스의 확산 및 폭발 Simulation

장창봉(Chang-Bong Jang),이향직(Hyang-Jik Lee),이민호(Min-Ho Lee),민동철(Dong-Chul Min),백종배(Jong-Bae Back),고재욱(Jae Wook Ko),권혁면(Hyuck-Myun Kwon) 한국가스학회 2012 한국가스학회지 Vol.16 No.5

현재 가연성 가스의 누출시 누출된 가스의 확산과 VCE에 의한 과압을 예측하기 위해 여러 모델들이 이용되고 있다. 그러나 이 모델들은 누출설비의 지형과 장애물 그리고 건물들의 영향에 대해서는 충분히 고려하지 않은 단순한 접근방법을 이용하고 있다. 이에 본 연구는 누출된 물질의 연소형태, 설비의 Geometry, 난류, 장애물, 바람의 영향등 여러 변수를 고려하여 보다 정확하게 분석할 수 있는 CFD(Computational Fluid Dynamics) Model을 검토함으로서 누출된 가스의 확산과정과 분포형태 그리고 폭발시 화염과 과압의 결과를 2D와 3D의 가상공간에서 제시하였다. 이러한 CFD분석결과는 폭발에 대한 리스크 분석과 리스크 기반의 설계에 있어 유용하게 활용될 것으로 판단된다. Various models are currently applied to predict the dispersion of leaked combustible gas and overpressure from a vapor cloud explosion(VCE). However, those models use simple approaches where topography and barriers of anti-leakage facilities and the effects of buildings were not sufficiently taken into considerations. For this reason, this study has proposed the dispersion process of leaked gas, distribution patterns, and flames and overpressure generated from gas explosions in 2D and 3D virtual spaces by reviewing more accurately analyzable computational fluid dynamics(CFD) model by considering various variables including combustion types of leaked substances, geometry of facility, warm currents, barriers, the influence of wind, and others. The CFD analysis results are anticipated to be usefully applied for the risk analysis of explosion and for the risk-based design.

A numerical study on the feasibility of predicting the resistance of a full-scale ship using a virtual fluid

김관우,백광준,이순현,이준희,권수연,오도한 대한조선학회 2024 International Journal of Naval Architecture and Oc Vol.16 No.-

In general, the resistance of a real ship is estimated using an extrapolation method after doing experimental tests or numerical simulations with a model scale ship. Since the only Froude similarity is applied in the model test and simulation, the flow characteristics between the model and real ships could be different due to the inconsistency of Reynolds number. However, in the Computational Fluid Dynamics (CFD), the Froude and Reynolds numbers can be satisfied simultaneously because a fluid with virtual properties can be applied. This study investigated the effect of turbulence models and scales for a flat plate. And then the hydrodynamic feasibility of using a virtual fluid was investigated through numerical analysis. The resistance performance and flow structure of the ship were analysed by applying the virtual fluid, and they were confirmed how well these values and flow characteristics simulate the full-scale with a real fluid. This study shows that the results of a full-scale can be obtained at model scale by applying a virtual fluid instead of full-scale numerical simulations that require more computational resources.

CFD-CRN validation study for NOx emission prediction in lean premixed gas turbine combustor

누엔후트룩,김승한,박정규,정승채,Shaun Kim 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.10

Numerical prediction of NO x formation in combustion device is becoming more important because of stringent legislation. This work describes the validation of CFD-CRN (Computational fluid dynamics-Chemical reactor network) method for NO x emission predictions for a gas turbine combustor design. Steady state 3-D CFD models of the gas turbine combustor were generated using ANSYS FLUENT v14.5. The results of 3-D CFD simulation were presented, which gave insight into the flow field, temperature, and equivalence ratio distribution of the gas turbine combustor operating natural gas (CH 4 ). The Chemical reactor networks (CRN) with 4 PSRs for simple model and 12 PSRs for detailed model were developed based on Computational fluid dynamics (CFD). The predictions of the exhaust emissions in the CRN model were carried out using CHEMKIN code and full GRI 3.0 chemical kinetic mechanism. This paper discussed the validation of the CFD simulation and CFD-CRN method by comparing the predicted temperature and chemical species of both models. Model combustor tests were conducted at various equivalence ratios. The CFD-CRN predicted NO x emissions at the combustor exit were compared with experimental values. The detailed CRN predictions of NO x emissions showed better agreement with experimental values compared with the simple CRN predictions. However, the simple CRN also showed reasonable predictions. Also, the NO formation pathway analysis was carried out to gain deeper understanding of the relative contributions of the four NO formation mechanisms.