• Journal of Drive and Control
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• v.21 no.2
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• pp.8-14
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• 2024

This paper investigates the jetting characteristics of an aerosol jet printing (AJP) process as a function of design and operating conditions. The governing equations of the AJP system are derived for experimentation and analysis. To understand the characteristics of the AJP system, this thesis analyzes the jetting characteristics as a function of the flow rate of the carrier gas and the sheath gas, and the variation of the linewidth with the nozzle exit size based on particle tracking. This thesis focuses on computational fluid dynamics (CFD), which is a computer simulation. The particle tracking results obtained by CFD were analyzed using MATLAB. CFD analytical models can be analyzed in environments with different conditions and consider more specific situations than mathematical computational models. The validity of the CFD analysis is shown by comparing the experimental results with the CFD analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.6
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• pp.532-540
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• 2008

Recently there are growing interests in calculating aerodynamic characteristics of aircraft configurations with structural deformation using the FSI(Fluid-Structure Interaction) system in which CFD(Computational Fluid Dynamics) and CSD(Computational Structure Dynamics) modules are coupled. In this paper the FSI system comprised of CAD, CFD, CSD, VSI(Volume Spline Interpolation) and grid deformation modules was constructed in order to investigate aerodynamic characteristics of the deformed shape. In the process VSI and grid generation modules are developed to combine CSD and CFD routines and to regenerate the aerodynamic grids for the deformed shape, respectively. For the CFD and CSD analysis, commercial programs FLUENT and NASTRAN were used. As a test model, DLR-F4 wing configuration was chosen and its aerodynamic characteristics were calculated by applying the static FSI system. It was shown that lift and drag coefficients of the wing at mach number 0.75 are reduced to 20.26% and 18.5%, respectively, owing to the structural deformation.

• The KSFM Journal of Fluid Machinery
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• v.16 no.3
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• pp.26-31
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• 2013

In present 3D CFD study, the method for determining leakage and rotordynamic coefficients of a plain-gas seal is suggested by using the relative coordinate system for steady-state simulation. In order to find the effect of pre-swirl speed at seal inlet, pre-swirl velocity is included as a parameter. Present analysis is verified by comparison with results acquired from Bulk-flow analysis code and published experimental results. The results of 3D CFD rotordynamic coefficients of direct stiffness(K) and cross-coupled stiffness(k) show improvements in prediction. As pre-swirl speed at seal inlet increases, k also increases to destabilize system. However, pre-swirl speed at seal inlet does not show sensitivity to the leakage and rotordynamic coefficients of K and damping(C).

• Atmosphere
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• v.22 no.1
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• pp.109-115
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• 2012

We parallelized the CFD_NIMR model, which is a numerical meteorological model, for best performance on both of distributed and shared memory parallel computers. This hybrid parallelization uses MPI (Message Passing Interface) to apply horizontal 2-dimensional sub-domain out of the 3-dimensional computing domain for distributed memory system, as well as uses OpenMP (Open Multi-Processing) to apply vertical 1-dimensional sub-domain for utilizing advantage of shared memory structure. We validated the parallel model with the original sequential model, and the parallel CFD_NIMR model shows efficient speedup on the distributed and shared memory system.

• Journal of Aerospace System Engineering
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• v.2 no.2
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• pp.46-50
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• 2008

Aerodynamic characteristics, such as drag and lift, play an important role in automobile design under certain speed conditions. Such characteristics are essential to design an automobile since they are directly related to automobile's performance such as passenger safety and fuel consumption. There is a huge demand for the automobile to have safe performance at high speed. Reduction in drag is also important and it could lead to the solution of air flow induced noise and dust problems. The objective of this research is to find out the aerodynamic differences between conventional side mirror and a modified one using CFD. Although drag generated around a side mirror is only about 7% of the total drag when a car runs, it is very closely related to driver's field of vision and noise generation. CFD simulation of the flowfield around a car side-view mirror was performed using a commercial code; Gambit and FLUENT.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.929-929
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• 2005

In this study, computational demonstrations for the flutter suppression are presented for the 3-DOF airfoil system with oscillating flap. Advanced computational methods such as computational fluid dynamics (CFD) and computational structural dynamics (CSD) are used and a simultaneous coupling method has been developed to accurately conduct flutter analyses. In addition, optimal control theory is integrated into the CFD based flutter analysis method to construct the coupled aeroservoelastic analysis system for the airfoil with oscillating flap. For a well-defined typical section model, fundamental unsteady aerodynamics and flutter characteristics are investigated. Finally, to show the effectiveness of flutter control the physical aeroelastic responses are directly compared between the open loop and the closed loop systems.

• Journal of Environmental Impact Assessment
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• v.20 no.3
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• pp.337-348
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• 2011

Urban environmental problem became one of major issues during its urbanization processes. Environmental impacts are assessed during recent urban planning and development. Though the environmental impact assessment considers meteorological impact as a minor component, changes in wind environment during development can largely affect the distribution pattern of air temperature, humidity, and pollutants. Impact assessment of local wind is, therefore, a major element for impact assessment prior to any other meteorological impact assessment. Computational Fluid Dynamics (CFD) models are utilized in various fields such as in wind field assessment during a construction of a new building and in post analysis of a fire event over a mountain. CFD models require specially formatted input data and produce specific output files, which can be analyzed using special programs. CFD's huge requirement in computing power is another hurdle in practical use. In this study, a CFD model and related software processors were automated and integrated as a microscale wind environmental impact assessment system. A supercomputer system was used to reduce the running hours of the model. Input data processor ingests development plans in CAD or GIS formatted files and produces input data files for the CFD model. Output data processor produces various analytical graphs upon user requests. The system was used in assessing the impacts of a new building near an observatory on wind fields and showed the changes by the construction visually and quantitatively. The microscale wind assessment system will evolve, of course, incorporating new improvement of the models and processors. Nevertheless the framework suggested here can be utilized as a basic system for the assessment.

• Nuclear Engineering and Technology
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• v.46 no.3
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• pp.363-372
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• 2014

In this study, we proposed a newly designed sulfuric acid transfer system for the sulfur-iodine (SI) thermochemical cycle. The proposed sulfuric acid transfer system was evaluated using a computational fluid dynamics (CFD) analysis for investigating thermodynamic/hydrodynamic characteristics and material properties. This analysis was conducted to obtain reliable continuous operation parameters; in particular, a thermal analysis was performed on the bellows box and bellows at amplitudes and various frequencies (0.1, 0.5, and 1.0 Hz). However, the high temperatures and strongly corrosive operating conditions of the current sulfuric acid system present challenges with respect to the structural materials of the transfer system. To resolve this issue, we designed a novel transfer system using polytetrafluoroethylene (PTFE, $Teflon^{(R)}$) as a bellows material for the transfer of sulfuric acid. We also carried out a CFD analysis of the design. The CFD results indicated that the maximum applicable temperature of PTFE is about 533 K ($260^{\circ}C$), even though its melting point is around 600 K. This result implies that the PTFE is a potential material for the sulfuric acid transfer system. The CFD simulations also confirmed that the sulfuric acid transfer system was designed properly for this particular investigation.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.152-157
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• 1999

For the simulation of the blood flow in coronary artery, the system modeling of coronary hemodynamics is combined with CFD technique. The blood flow in coronary artery interacts with the global coronary circulation. Especially in case of the coronary artery with stenosis, the interaction plays an important role in the hemodynamics of the circulation. In this study we present a combined numerical approach using both the CFD technique for flow simulation and the global system model of coronary circulation. We use a lumped parameter model for the global simulation of coronary circulation whereas the finite element method is employed to compute the viscous flow field in stenosed coronary artery, The time variation of the pressure drop due to stenosis is obtained from the proposed numerical method. Numerical results shows that the flow resistance and pressure drop due to stenosis has a relatively large value in systole.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.1-7
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• 2017

The mixing of water and chemicals is an important process in the water purification plant. In this paper, we compare PDM(pump diffusion mixer) and hydraulic mixer at the basin in the mixing process. The proper flow rates are predicted and compared in both mixers using CFD technique. As a result, the flow rate of purifier chemical liquid should be 5% of that of water for the optimal performance of mixing process. The characteristics of the two mixing methods are compared with each other for strong and weak points on the operation of the purification system, discussed in the view point of CFD simulations.