• 한국가시화정보학회지
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• 제19권3호
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• pp.115-122
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• 2021

Oral cancer surgery typically consists of resection of lesion, neck dissection and reconstruction, and it has an impact on the position of hyoid bone. Therefore, morphological change of airway can occur since the geometric parameter of airway is correlated with the hyoid bone. Airflow is affected by geometry of the airway. In this study, flow characteristics were compared between pre- and post-surgery models by both particle image velocimetry (PIV) and numerical simulation. 3D model of upper airway was reconstructed based on CT data. Velocity is accelerated by the reduced channel area, and vortex and recirculation region are observed in pre- and post-surgery models. For the post-surgery model, high pressure distribution is developed by significantly decreased hydraulic diameter, and the longitudinal flow stream is also interrupted.

• 한국가시화정보학회지
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• 제20권1호
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• pp.52-63
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• 2022

Direct numerical simulation of blood flow in a stenosed, patient-specific carotid artery was conducted to explore the transient behavior of blood flow with special emphasis on the wall-shear stress distribution over the transition region. We assumed the blood as an incompressible Newtonian fluid, and the vessel was treated as a solid wall. The pulsatile boundary condition was applied at the inlet of the carotid. The Reynolds number is 884 based on the inlet diameter, and the maximum flow rate and the corresponding Womersley number is approximately 5.9. We found the transitional behavior during the acceleration and deceleration phases. In order to quantitatively examine the wall-shear stress distribution over the transition region, the probability density function of the wall-shear stress was computed. It showed that the negative wall-shear stress events frequently occur near peak systole. In addition, the oscillatory shear stress index was used to further analyze the relationship with the negative wall-shear stress appearing in the systolic phase.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 창립기념학술대회
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• pp.44-68
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• 1995

In the present paper, visualization techniques in fluid dynamic experiments such as Schlieren photograph are numerically simulated so that the same output as the experimental flow visualization can be obtained from the computed results for the fair comparison. Numerical methods to simulate optical visualizations, that are Schlieren photograph, shadowgraph and interferogram, are considered. Some examples of pictures obtained by the present methods show the importance of the simulations of visualization techniques for the correct comparisons of the computations and experiments.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2008년도 춘계학술 발표회
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• pp.101-108
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• 2008

Polymer electrolyte membrane (PEM) fuel cells are promising power generation devices which are ideal for residential and automobile applications, thanks to their fast transient characteristics. However, liquid water produced in PEM fuel cells should be properly managed to enhance the performances and durabilities of the cells. In this study, a visualization experiment was conducted to investigate the flow behavior of water droplets in cathode channels. The visualization experiment was done with four different model flow channels which were made by varying the material (Acrylic and Teflon) and the channel width (1 mm and 2 mm). Acrylic is hydrophilic (contact angle is about $80^{\circ}$) while Teflon is hydrophobic (contact angle is about $120^{\circ}$). A computational fluid dynamics (CFD) analysis was also performed to compare the observed and the simulated two-phase water/air flow characteristics in cathode channels. The computational models were made to be consistent with the geometries and surface properties of the model flow channels. Both the experimental and numerical results showed that the Teflon cathode channel with 1 mm width has the best water management performance among four model flow channels considered. A close correlation was found between the experimental visualization results and the numerical CFD simulation results.

• 한국가시화정보학회지
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• 제2권2호
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• pp.32-37
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• 2004

In this paper the numerical method with a zonal embedded grid system for an incompressible flow within a semi-circular container is presented. The algorithm is validated by its application to some typical flow models including the spin-up flow inside a semi-circular geometry. Flow visualization for the spin-up flows was used by PIV. The results show that at high Reynolds numbers the cyclonic cell at the left-hand side region moves along the circular wall and merges with the cell at the right-hand side region.

• 대한기계학회논문집B
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• 제20권12호
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• pp.3970-3979
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• 1996

A fluid flow inside a circular cylinder subject to horizontal, circular oscillation is analyzed numerically and experimentally. The steady streaming velocities at the edges of the boundary layers on the bottom and side surfaces of the cylinder obtained in the previous paper are used as the boundary conditions in the governing equations for the steady flow motion in the interior region. The Stokes' drift velocity obtained in the previous paper also constitutes the Lagrangian velocity which is used in the momentum equations. It turns out that the interior steady flow is composed of one cell, ascending at the center and descending near the side surface, at the streaming Reynolds number 2500. However, at the streaming Reynolds number 25, the flow field is divided into two cells resulting in a descending flow at the center. The experimentally visualized flow patterns at the bottom surface agree well with the analytical solutions. The visualization experiment also confirms the flow direction as well as the center position of the cell obtained by the numerical solutions.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.35-41
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• 2004

A numerical investigation has been made for flows in an axisymmetric circular cylinder with a rotating cone located at the bottom of the container. The axisymmetric container is completely filled with a viscous fluid. Major parameter for the present research is the vertex angle of the cone, otherwise Reynolds number of fluid and aspect ratio of the vessel is fixed. Main interest is in vortex breakdown of meridional circulation by rotation of the cone with respect to the longitudinal axis of the cylinder. The method to this problem is numerically to integrate momentum and continuity equations on a generalized body fitted grid system. The pattern of vortex breakdown is quite different from that in a right circular cylinder with flat end wall disks. Flow visualization photographs of a preceeding work are compared with the present numerical results.

• 한국가시화정보학회지
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• 제17권2호
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• pp.67-72
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• 2019

In this study, we investigate the non-reacting and reacting performance of single nozzle for post H class gas turbine by using commercial CFD tool, CONVERGE, based on adaptive mesh refinement. By varying swirl number and mixing length of base nozzle design. Through the numerical analysis, basic phenomena can be well described with respect to fuel concentration for non-reacting flow, temperature distribution, velocity vector and combustion outlet temperature distribution for reacting flow. However, there are rooms for improvements in model accuracy by comparing test results. Comparison between numerical analysis are planning for further study.

• 한국가시화정보학회지
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• 제13권3호
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• pp.29-34
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• 2015

The interaction between a normal shock wave and a boundary layer along a wall surface in internal compressible flows causes a very complicated flow. This interaction region containing shock train and mixing region is called as pseudo-shock waves. Pseudo-shock waves in the divergent part of a rectangular nozzle have been investigated by using large-eddy simulation (LES). LES studies have been done for the complex flow phenomena of three-dimensional pseudo-shock waves. The LES results have been validated against experimental wall-pressure measurements. The LES results are in good agreement with experimental results. Pseudo-shock length and corner separation have been studied in three-dimensional LES model. Comparison of centerline pressure measurement and 3D visualization measurement has been discussed for the corner separation position. It has been concluded that the pseudo-shock length should be measured by using 3D visualization measurement.

• Transactions on Electrical and Electronic Materials
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• 제6권2호
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• pp.39-45
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• 2005

Numerical and visualization procedures are used in a finite difference grid to analyze and better understand the heat transfer in the MEMS based air micro-jet array (MIA) impingement cooling device. The Navier-Stokes (NS) equations with incompressible flow are solved using an implicit procedure. The temperature contour and velocity vector visualization diagrams are used for illustration. The computed temperature distribution at the bottom of the MIA is in good agreement with the experimental measurement data. The parameters are investigated to improve the efficiency of heat transfer in the MIA. The optimum configuration of the MIA is suggested. The present modeling explains the flow phenomenon and yields valuable information to understand the flow and heat transfer in MIA.