• 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.

• 한국세라믹학회지
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• 제31권5호
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• pp.552-560
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• 1994

A composite of TiB2-Al2O3 system was successfully prepared from a mixture of TiO2, B2O3, and Al by self-propagating high temperature synthesis (SHS) with a novel characteristic, utilizing the internal oxidation heat of aluminium metal of the mixture, instead of by a conventional technique, externally heating a mixture of Ti, B and Al2O3. From a mixture with B/Ti molar ratio of =2.0, pure two phases of TiB2 and $\alpha$-Al2O3 with good crystallinity and small, uniform sizes were formed. However, when the B/Ti molar ratio of the mixture goes to a value less than 2.0, in addition to the above main minerals, a small smounts of metastable phases such as TiB and Ti3B4 were formed. It was found that about 60%, the optimum green density of compacts gave their highest reaction rate and temperature during SHS process. TiB2-Al2O3 system composite with B/Ti molar ratio of =2.0 could be pressurelessly sintered even at 190$0^{\circ}C$ under Ar gas flows without any addition of sintering aids, showing their good properties such as 91.2% in relative density, 2750 kgf/$\textrm{mm}^2$ in Vickers hardness and 2620 kgf/$\textrm{cm}^2$ in flexural strength.

• 한국초전도ㆍ저온공학회논문지
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• 제15권4호
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• pp.26-29
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• 2013

Smart fault current controller (SFCC) proposed in our previous work consists of a power converter, a high temperature superconducting (HTS) DC reactor, thyristors, and a control unit [1]. SFCC can limit and control the current by adjusting firing angles of thyristors when a fault occurs. SFCC has complex structure because the HTS DC reactor generates the loss under AC. To use the DC reactor under AC, rectifier that consists of four thyristors is needed and it increases internal resistance of SFCC. For this reason, authors propose a hybrid type superconducting fault current limiter (SFCL). The hybrid type SFCL proposed in this paper consists of a non-inductive superconducting coil and two thyristors. To verify the feasibility of the proposed hybrid type SFCL, simulations about the interaction of the superconducting coil and thyristors are conducted when fault current flows in the superconducting coil. Authors expect that the hybrid type SFCL can control the magnitude of the fault current by adjusting the firing angles of thyristors after the superconducting coil limits the fault current at first peak.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.292-295
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• 2008

In a SCWR (SuperCritical pressure Water cooled Reactor), the coolant temperature initially at below the pseudo-critical temperature at the bottom of a reactor core increases as the coolant flows upward through the sub-channels of the fuel assemblies, and it finally becomes higher than the pseudo-critical temperature when it leaves the reactor core. At certain conditions, heat transfer deterioration occurs near the pseudo-critical temperature and it may cause a drastic rise of the fuel surface temperature resulting a fuel failure. Therefore, an accurate estimation of the heat transfer coefficient is very important for the thermal-hydraulic design of a reactor core. An experiment on heat transfer to the vertically upward flowing $CO_2$ at a supercritical pressure in a circular tube were performed at KAERI. The internal diameter of the test section is 6.32 mm, which corresponds to the hydraulic diameter of a sub-channel in the conceptional design proposed by KAERI. The test range of the mass flux is 285 to 1200 kg/m$^2$s and the maximum heat flux is 170 kW/m$^2$. The inlet pressure is maintained at 8.12 MPa, which is 1.1 times the critical pressure. A new correlation, which covers both the normal and deterioration heat transfer regimes was proposed and compared with the estimations by exiting correlations.

• 대한기계학회논문집B
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• 제24권8호
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• pp.1128-1138
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• 2000

Pumping action in ejector systems is generally achieved through the mixing of a high-velocity and high-energy stream with a lower-velocity and lower-energy stream within a duct. The design and performance evaluation of the ejector systems has developed as a combination of scale-model experiments, empiricism and theoretical analyses applicable only to very simplified configurations, because of the generic complexity of the flow phenomena. In order to predict the detailed performance characteristics of such systems, the flow phenomena throughout the operating regimes of the ejector system should be fully understood. This paper presents the computational results for the two-dimensional supersonic ejector system with a second throat. The numerical simulations are based on a fully implicit finite volume scheme of the compressible Reynolds-averaged Navier-Stokes equation in a domain that extends from the stagnation chamber to the diffuser exit. For a wide range of the operating pressure ratio the flow field inside the ejector system is investigated in detail. The results show that the supersonic ejector systems have an optimal throat area for the operating pressure ratio to be minimized.

• 한국유체기계학회 논문집
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• 제15권6호
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• pp.85-91
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• 2012

Numerical simulations on a single stage transonic compressor which is developed by Korea Aerospace Research Institute are carried out and their results are compared with experimental data for cross validations. Comparisons between experimental data and numerical simulation results show good agreements on a performance curve, static pressure and total pressure distributions. CFD results show that there is a clear interaction between tip leakage flow and normal shock in the rotor passage. Tip leakage flows are almost dissipated after the strong normal shock and it forms a strong recirculation near the blade tip. Also a large separation region grows on the suction surface just after the normal shock. As the pressure ratio and blade loading increase, the normal shock line moves upstream and it starts to deviate from the blade leading edge. Then the tip leakage flow does not overcome the strong adverse pressure gradient and flow blockage originated from the tip recirculation region. As a result, the tip leakage flow heads for the neighboring blade leading edge, which results in a compressor stall.

• Tribology and Lubricants
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• 제33권6호
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• pp.256-262
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• 2017

Molten zinc plating is a process in which zinc is thinly coated over a metallic or non-metallic surface. It is used in various industrial fields for corrosion resistance and decoration. During the process, a steel sheet is passed through a roll that rotates inside the molten zinc liquid in the temperature range of $460^{\circ}C$ to $680^{\circ}C$, and the plating liquid flows into the roll causing abrasion and erosion of the roll surface. This problem is known to accelerate the replacement cycle of the roll and cause considerable economic loss owing to production line stoppage. Here, we propose a mechanism that operates at high temperature and pressure with a labyrinth type seal design to resolve this problem. We theoretically investigate the flow of the plating solution inside the seal and compute the minimum rotation speed required to prevent the plating solution from entering the seal chamber. In addition, we calculate the thermal deformation of the seal during operation and display thermally deformed dimensions at high temperatures. To verify the theoretical results, we perform experiments using pilot test equipment working in the actual plating environment. The experimental results are in good agreement with theoretical results. We expect our results to contribute towards the extension of the roll's life span and thereby reduce the economic losses.

• 한국자동차공학회논문집
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• 제4권1호
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• pp.187-197
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• 1996

Many investigations have been made to determine the pressure drop and heat transfer characteristics for single phase flow in tape generated swirl flow. But few studies have been carried out to investigate the heat transfer in two component, two phase swirl flow with non-boiling. An experimental study has been conducted to determine the effects of tape twist ratios on two phase convective heat transfer coefficients, pressure drop, and void fraction distribution in a non-boiling, air-water, two phase flow. The flow conditions were both swirl and non swirl flows. The internal diameter of the test section is 42.5mm. The tape twist ratios of pitch to diameter ratio varied from 4.0 to 10.6. The heating conditions were isothermal and nonisothermal. The flow patterns identified with experiments were bubbly, bubbly-slug, slug, and slug-annular flow in up-flow. This study has concluded that no significant difference in void fraction distribution were observed both isothermal and nonisothermal conditions, the pressure drop for two phase flow with twisted tape swirler increase as the tape twist ratio decrease, and that values of two phase heat transfer coefficient increase when the tape twist ratio decreases.

• 한국건설관리학회:학술대회논문집
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• 한국건설관리학회 2001년도 학술대회지
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• pp.81-87
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• 2001

동적 변화가 상존하는 건설환경에서, 보수·리모델링 프로그램의 관리자는 자원하의 복수 프로젝트를 조정·관리하는데 어려움을 겪게 된다. 프로그램에 내재하는 불확실성과 상호종속성으로 인해, 단위작업의 지연과 그로 인한 연쇄적인 공정계획의 동요는 프로그램 전체의 안정성과 관리가능성을 저해한다. 본 논문은 먼저 건설관리에 적용되었던 생산관리기법들이 프로그램관리에 적용될 수 있는가를 살펴본 후, 프로그램 내부의 자원유동의 흐름에 주기적으로 버퍼를 설치하는 공정 안정화 모델을 제안하고자 한다. 몬테-칼로 시뮬레이션에 의한 비교실험으로 제안된 버퍼 관리모델의 성능을 프로그램의 생산성, 유연성, 그리고 안정성의 관점에서 분석하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.419-426
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• 2004

A three-dimensional computation was conducted to understand effects of the inlet boundary layer thickness on the loss mechanism in a low-speed axial compressor operating at the design condition(${\phi}=85\%$) and near stall condition(${\phi}=65\%$). At the design condition, the flow phenomena such as the tip leakage flow and hub comer stall are similar independent of the inlet boundary layer thickness. However, when the axial compressor is operating at the near stall condition, the large separation on the suction surface near the casing is induced by the tip leakage flow and the boundary layer on the blade for thin inlet boundary layer but the hub corner stall is enlarged for thick inlet boundary layer. These differences of internal flows induced by change of the boundary layer thickness on the casing and hub enable loss distributions of total pressure to be altered. When the axial compressor has thin inlet boundary layer, the total pressure loss is increased at regions near both casing and tip but decreased in the core flow region. In order to analyze effects of inlet boundary layer thickness on total loss in detail, using Denton's loss models, total loss is scrutinized through three major loss categories in a subsonic axial compressor such as profile loss, tip leakage loss and endwall loss.