• Wind and Structures
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• v.1 no.3
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• pp.271-284
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• 1998

This paper uses the numerical simulation to investigate the interference effect of 3-D turbulent flow around two high rise buildings in proximity at the different relative heights, gaps, and wind velocities. The computer program used to carry out the simulation is based on the control volume method and the SIMPLEST algorithm. The ${\kappa}-{\varepsilon}$ model was used to simulate turbulence effects. Since the contracted flow between two adjacent buildings enhances the strength of vortex shedding from the object building, the pressure coefficient on each side wall of the object building is generally increased by the presence of apposed building. The effect is increased as the relative height or the gap between the two buildings decreases. The velocity on the vertical center line between two buildings is about 1.4 to 1.5 times the upstream wind velocity.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.5
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• pp.662-670
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• 1999

A numerical prediction was performed to clarify the air motion in the cylinder of an axisymmet-ric four-stroke reciprocating engine at its intake and compression stage. A scheme of finite volume method is used for the calculation. Modified $k-{\varepsilon}$ turbulence model is adopted and wall function is applied to the grids near the wall. The predicted mean velocity and rms velocity profiles showed a reasonable agreement with an available experimental data at its intake and compression stage. The predicted in-cylinder flow fields show that a strong turbulent twin vortex structure is pro-duced during induction but it commences to decay rapidly around inlet valve closure. The mean velocity continues to fall to a low level during compression but the turbulence intensity attains an approximate constant level.

• Journal of ILASS-Korea
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• v.24 no.3
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• pp.122-129
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• 2019

Flow uniformity in aftertreatment system is an important factor in determining uniform catalytic reaction and filtration. In this study, variety types of DOC-DPF system design were analyzed to increase flow uniformity. For this analysis, ANSYS Fluent was used with porous media setup for DOC and DPF. Turbulent flow was modeled by standard $k-{\varepsilon}$ model excepting porous media. Uniformity index was utilized to evaluate the flow uniformity quantitatively. Reference design showed low velocity region because two large vortex were generated before baffle. When radius of DOC-DPF system was increased, exhaust pressure acting on the inlet decreases and velocity distribution was shifted to one side. When inlet pipe was set to axial center of DOC-DPF system velocity distribution was symmetric. However, flow was not dissipated until the front end of DOC and showed higher uniformity index. When the volume of DOC was reduced while fixed volume of entire DOC-DPF system and baffle plate is located downstream of the DOC-DPF system, there was improvement in uniformity index.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.60-65
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• 2001

The projectile afterbodies for zero-lift drag reduction has been analyzed using the Navier-Stokes equations with the $\kappa-\epsilon$ turbulence model. The numerical method of a second order upwind scheme has been used on unstructured adaptive meshes. Base drag reduction methods that have been found effective on axisymmetric bodies include boattailing, base bleed, base comustion, locked vortex afterbodies and multistep afterbodies. In this paper, the charateristics of turbulence flow have been studied for geomeries of multistep afterbodies. The important geometrical and flow parameters relevant to the design of such afterbodies have been identified by number, length and height of step. The flow over multistep afterbodies has been analyzed including expansion waves, recompression waves, recirculating flow, shear flow and wake flow. The numerical results have been compared and analyzed with the experimental datum.

• Journal of computational fluids engineering
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• v.9 no.4
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• pp.34-40
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• 2004

It is known that the non-planar model of bypass is more profitable to suppress the development of intimal hyperplasia that tends to occur preferentially in regions of low time averaged shear stress and rapid temporal changes in wall shear stress. In this study it was numerically simulated the blood flow in an coronary artery grafted by artificial bypass to determine the flow characteristic variations due to the anastomosis angle changing. 5 different non-planar anastomosis angle models such as 45°, 60°, 90°, 120° and 135° were considered. When the anastomosis angle is higher, the backward flow region is spatially extended near the downstream region of the anastomosis because of the development of horseshoes vortex. For the case of the nan-planar 45° and 60° of anastomosis, the area of low-OSI zone was decreased by 26% and 13% respectively and the time averaged wall shear stress was increased by more than 55% as compared with 45° of planar model. However, both of the area of the low-OSI zone and the time averaged wall shear stress of 90°, 120° model were significantly increased.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.1
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• pp.134-141
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• 2000

In this study, a scaled model chamber was built to investigate ventilation characteristics of the Under floor Air-conditioning System. Experimental study was performed in model for cargo-oil pump room with inlet and outlet by visualization equipment with laser apparatus. Instant simultaneous velocity vectors at whole field were measured by 2-D PIV system(CACTUS'2000) which adopted two-frame grey-level cross correlation algorithm. The flow pattern reveals the large scale counterclockwise forced-vortex rotation from upside louver to lower scupper toward diagonal corner and also found small eddies at bottom layer

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.623-626
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• 2002

The object of present study is to find the flow characteristics of centrifugal turbomachinery according to the volute shape change. The experiments were carried out for two model; volute-A designed by free vortex conditions and volute-B designed for use in high mass flow rate conditions using the volute-A test results, Flow measurements were taken in shrouded impeller with 12 backward type blades by using a five-hole pilot-tube and carried out in 4 flow rate, $Q/Q_d\;=0,43,\;1.0,\;1.27,\;1,47$, respectively, For volute-B, we found that pressure distribution was more uniform at high flow rate and from $Q/Q_d\;:\;0,43\;to\;Q/Q_d\;:\;1,20$, losses decreased and efficiency increased compare with volute-A.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.10-12
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• 2008

Hemodynamic features of blood flow in the abdominal aorta aneurysm (AAA) are very important, because they are closely related with the rupture of aneurysm to death. It has been considered that the wall shear stress of blood flows influences the formation, growth, and rupture of AAA. On this account, it is important to understand the flow structure of blood in the aneurysm. In this study, the whole velocity field information inside a typical AAA was measured using an in vitro AAA model under the pulsatile flow condition. The vessel geometry was reconstructed based on the computerized tomography (CT) data of a patient. The AAA model was made by using a rapid prototyping (RP) method, based on the reconstructed vessel geometry. Velocity fields in the AAA model were measured at different pulsatile phases using a PIV (particle image velocimetry) system. As experimental results, a large-scale vortex is formed inside the AAA model and the vortices located near the AAA wall are supposed to increase the local pressure and wall shear stress. In this study, the AAA wall stress found to be was one of the most important governing parameters giving rise to the ruptured aneurysm.

• Journal of ILASS-Korea
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• v.11 no.3
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• pp.168-175
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• 2006

The static pressure distribution and flow characteristics inside the high-pressure swirl spray were investigated by measuring the static pressure inside the spray and applying the computational fluid dynamics (CFD). The static pressure difference between inner and outer part of spray was measured at different axial locations and operating conditions using a piezo-resislive pressure transducer. To obtain the qualitative value of swirl motion at different operating conditions, the spray impact-pressure at the nozzle exit was measured using a piezo-electric pressure transducer, and the flow angle was measured using a microscopic imaging system. The flow characteristics inside the high pressure swirl spray was simulated by the 1-phase 3-dimensional CFD model. The effect of pressure alternations on spray development was discussed with macroscopic spray images and a mathematical liquid film model. The results showed that the static pressure drop is observed inside the swirl spray as a result of the dragged air motion and the centrifugal force of the air. The recirculation vortex inside the spray was also observed inside the swirl spray as a result of the adverse pressure gradient along the axial locations. The results of analytical liquid film model and macroscopic spray images showed that the static pressure structure is one of the main parameters affecting the swirl spray development.

• 연구논문집
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• s.25
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• pp.55-65
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• 1995

Three-dimensional incompressible turbulent flow fields within the passage of the steam turbine nozzle with/without tip clearance have been simulated by solving the Navier-Stokes equations with SIMPLE scheme. The extended k-e model is applied to modeling the Reynolds stresses. Grids in the computational domain are generated by solving the Poisson's equations to improve the smoothness and orthogonality. Flow losses, secondary flow, velocity profiles, and deviation angles are obtained. The computated results without tip clearance show good agreement with the experimental data.