• 한국수소및신에너지학회논문집
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• 제25권1호
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• pp.97-104
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• 2014

In a coal gasifier for IGCC, hot syngas leaving the gasifier at about 1550oC is rapidly quenched by cold syngas recycled from the gas cleaning process. This study investigated the flow and heat transfer characteristics in the gas quench system of a commercial IGCC process plant under different operating pressures. As the operating pressure increased from 30 bar to 50 bar, the reduced gas velocity shortened the hot syngas core. The hot fly slag particles were retained within the core more effectively, and the heat transfer became more intensive around the hot gas core under higher pressures. Despite the high particle concentrations, the wall erosion by particle impaction was estimated not significant. However, large particles became more stagnant in the transfer duct due to the reduced gas velocity and drag force under higher pressures.

• Advances in aircraft and spacecraft science
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• 제7권3호
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• pp.229-249
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• 2020

This paper is the logical follow-up of four papers by the author on the subject "aerodynamics in Mars atmosphere". The aim of the papers was to evaluate the influence of two Mars atmosphere models (NASA Glenn and GRAM-2001) on aerodynamics of a capsule (Pathfinder) entering the Mars atmosphere and also to verify the feasibility of evaluating experimentally the ambient density and the ambient pressure by means of the methods by McLaughlin and Cassanto respectively, therefore to correct the values provided by the models. The study was carried out computationally by means of: i) a code integrating the equations of dynamics of an entry capsule for the computation of the trajectories, ii) two Direct Simulation Monte Carlo (DSMC) codes for the solution of the 2-D, axial-symmetric and 3-D flow fields around the capsule in the altitude interval 50-100 km. The computations verified that the entry trajectories of Pathfinder from the two models, in terms of the Mach, Reynolds and Knudsen numbers, were very different. The aim of the present paper is to continue this study, considering other aerodynamic problems and then to provide a contribution to a long series of papers on the subject "aerodynamics in Mars atmosphere". More specifically, the present paper evaluated and quantified the effects from the two models of: i) chemical reactions on aerodynamic quantities in the shock layer, ii) surface temperature, therefore of the contribution of the re-emitted molecules, on local (pressure, skin friction, etc.) and on global (drag) quantities, iii) surface recombination reactions (catalyticity) on heat flux. The results verified that the models heavily influence the flow field (as per the shock wave structure) but, apart from the surface recombination reactions, the effects of the different conditions on aerodynamics of the capsule are negligible for both models and confirmed what already found in the previous paper that, because of the higher values of density from the NASA Glenn model, the effects on aerodynamics of a entry capsule are stronger than those computed by the GRAM-2001 model.

• 한국항행학회논문지
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• 제16권6호
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• pp.900-909
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• 2012

저궤도 위성에 탑재하는 위성항법 수신기는 관측된 신호를 필터링하고 신호중단 시 궤도예측을 수행하는 항법필터를 장착하는데, 사용하는 위성동역학 모델이 필터성능을 주로 결정하게 된다. 본 연구에서는 항법필터에 필요한 정밀위성동역학 알고리듬을 연구하고 이를 계산하는 프로그램을 개발하였다. 정밀 중력가속도, 정밀좌표변환, 3체 중력, 대기저항, 태양복사압 모델을 결합하였으며, 해외 정밀궤도결정 프로그램을 이용하여 정확도를 검증하였다. 시뮬레이션과 실제 궤도 데이터를 사용하여 초기위치 정확도에 따른 궤도예측정확도를 분석 하였다. 개발된 모델은 위성탑재용 실시간 항법필터에 적용되는 동역학모델로는 충분한 정확도를 가지는 것을 확인하였다.

• 한국전산유체공학회지
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• 제20권2호
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• pp.46-51
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• 2015

In this paper, we have developed numerical model for particulated flow through narrow slit using Eulerian-Granular method. Commercial software (FLUENT) was utilized as simulation tool and main focus was to identify the effect from various numerical options for modeling of solid particles as continuos phase in granular flow. Gidaspow model was chosen as basic model for solid viscosity and drag model. And lun-et-al model was used as solid pressure and radial distribution model, respectively. Several other model options in FLUENT were tested considering the cross related effect. Mass flow rate of the particulate through the slit was measured to compare. Due to the high volume density of the stacked particulates above the slit, effect from various numerical options were not significant. The numerical results from basic model were also compared with experimental results and showed very good agreement. The effects from the characteristics of particles such as diameter, angle of internal friction, and collision coefficient were also analyzed for future design of velocity resistance layer in solar thermal absorber. Angle of internal friction was found to be the dominat variable for the particle mass flow rate considerably. More defined 3D model along with energy equation for complete solar thermal absorber design is currently underway.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.170-170
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• 2010

The energy conversion from the temperature difference between hot and cold source like ocean thermal energy conversion (OTEC), requires a long and large-diameter pipe (about 1000 to 10,000 meters long) to reach the deep water. The pipe diameter ranges from 2.8 meter for proposed early test systems, to 5 meter for large, commercial power generation systems. The pipe must be designed to resist collapsing pressures produced by water temperature and density differences, and the reduced pressure required to induce flow up the pipe. Other design considerations include the external-drag effect on the pipe due to ocean currents, and the wave-induced motions of the platform to which the pipe is attached. Various approaches to the pipe construction have been proposed, including aluminum, steel, concrete, and fiberglass. More recently, a flexible pipe construction involving the use of fiberglass reinforced plastic has been proposed. This report presents the results of a scaled fixed cold water pipe (CWP) model test program performed by EES(Engineering Equation Solver) to demonstrate the feasibility of this pipe approach.

• 대한조선학회논문집
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• 제54권3호
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• pp.250-257
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• 2017

It is desirable to have a way to predict the pressure drag due to various appendages attached to stern. As a mathematical model for these, a sphere and a singularity behind it, both in the uniform flow can be considered. We may use the Butler's sphere theorem to find the Stokes' stream function when the resulting flow is axisymmetric, and then the extended Lagally's theorem to get the force upon the sphere due to the singularity. Assuming the separation distance between the sphere and the singularity is small, the leading order approximation for the force is obtained and it is found out that if the separation distance and the square root of the strength of the dipole are of the same order, the effect of the image of the dipole with respect to the sphere is the most important.

• 한국군사과학기술학회지
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• 제18권3호
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• pp.300-308
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• 2015

Recently supercavitating underwater torpedo moving at high speed (over 200 knots) has been interested for their practical advantage of the dramatic drag reduction. Cavitator located in front of the torpedo plays an important role to generate a natural supercavity and control the motion of the object. Supercavity can be created artificially by injection of compressed gas from the rear of the cavitator at a relatively low speed. In this paper, we investigated physical characteristics of artificial supercavities through cavitation tunnel experiments. One of the main focuses of the study was to measure pressure inside the cavity, and examined variation of the gravity effects appearing according to different amount of injected air. It was also found that a stable supercavity could be sustained at injection rates less than that required to form the stable supercavity because of hysteresis effect.

• 한국자동차공학회논문집
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• 제9권1호
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• pp.75-83
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• 2001

In this paper, numerical analysis is used to find the effects of inclination of rear end on flow characteristic around an automobile. The reference slant angle of rear end is 28.6$^{\circ}$, the slant angle of rear end is decreased to 24$^{\circ}$, 26.6$^{\circ}$ and also increased to 31.6$^{\circ}$, 36.4$^{\circ}$. The 3-D incompressible Navier-Stockes equations are solved by the iterative time marching scheme. The computed surface pressure coefficients were compared with experimental results and a good agreement has been achieved. The A- and C-pillar vortex and other flow phenomena around the ground vehicle are evidently shown. The variation of aerodynamic coefficients of drag, lift with respect to inclination angle of rear end are systematically studied. The flow characteristic on the automobile surface with respect to change of inclination of rear end have been also studied.

• 대한기계학회논문집
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• 제11권6호
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• pp.877-883
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• 1987

본 연구에서는 이러한 경험적인면이 최소화되고 물리적 의미가 부여된 후류모 델을 제시하여 일반적인 형상에 대한 계산에 앞서 Celik등의 경우와 같이 원통 주위유 동장을 먼저 다루어 보고자 한다. 다른 방법들과는 달리 후류면의 길이를 조절하지 않고 후류면에서의 와도분포를 점차 감소시켜 후류영향이 자연적으로 감소되게 하였는 데, 이는 물체에서 떨어져 나간 와류(vortex)가 확산에 의해 점차 소멸해가는 점을 모 델링한 것이다. 본 계산은 경계층배제두께의 영향을 무시하고 후류모델에 필요한 박 리점은 실험치를 사용하여 수행하였다. 박리점의 예측은 기존의 경계층해법을 도입 하면 쉽게 해결할 수 있어 큰 문제가 아니라고 생각하며 다만 배제두께 영향은 Reyno- lds수에 따라 계산 결과에 다소 영향을 미칠 수 있게 되는데 이는 뒤에 다시 다루기로 한다.

• 한국항해항만학회지
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• 제41권2호
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• pp.33-38
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• 2017

A marine flapped rudder is designed to improve the effective lift generated by the rudder; this also improves the maneuverability of the ship. The flap is a high lift device installed at the trailing edge of the rudder to augment lift. In this paper, the characteristics of a thick flapped rudder are analyzed at a low Reynolds number with various ratios of flap chord length to total chord length and various aspect ratios, based on the computational fluid dynamics technique. The performance of the rudder with respect to lift, drag, and center of pressure are investigated, and the efficient ratio of flap chord length to total chord length and improved aspect ratio are determined. Ed: highlight - or 'superior'. As a case study, the flow on the flapped rudder of an NACA0021 section shape in free stream condition is simulated. The standard k-epsilon turbulence model is used to model the flow around the flapped rudder. The results indicate that the efficient ratio of the flap chord length to total chord length and aspect ratio are 0.3 and 1.4, respectively.