• 한국유체기계학회 논문집
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• 제14권2호
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• pp.11-16
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• 2011

This paper presents a numerical study of casing treatments on a centrifugal compressor stage to improve stability and the surge margin. High efficiency, a high pressure ratio, and a wide operating range are required for a high performance centrifugal compressor. In the present study, a ring groove arrangement was applied to the transonic centrifugal compressor. According to the numerical analysis using a commercial code ANSYS-CFX, the unstable phenomena limiting the range of the centrifugal compressors were compared with and without a ring groove. Although the ring groove decreased the efficiency, but increased the operating range by suppressing a flow separation at the leading-edge of the impeller especially near shroud part. Newly designed ring groove arrangement improved the compressor performance and increased the operating range of the compressor.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.471-477
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• 2003

The floating ring seal is often used in the turbopump (TP) unit of liquid rocket engine (LRE) owing to its inherent ability of minimizing the leakage flow and superior dynamic characteristics as well. This paper describes the test results concerned with the lock-up and dynamic characteristics of the floating ring seals in the turbopump. The characteristics of the floating ring seals were extracted from the frequency response function (FRF) by instrumental variable method. The experiment was tested at 7.0MPa and 0-24,800 rpm. And the test results were introduced about the dynamic characteristics of floating ring seal related with the eccentricity and attitude angle.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.501-517
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• 2020

Three-dimensional numerical simulations were performed to study the effects of flow direction and flow velocity on the flow regime behind a curved pipe represented by a curved circular cylinder. The cylinder is based on a previous study and consists of a quarter segment of a ring and a horizontal part at the end of the ring. The cylinder was rotated in the computational domain to examine five incident flow angles of 0-180° with 45° intervals at Reynolds numbers of 100 and 500. The detailed wake topologies represented by λ2 criterion were captured using a Large Eddy Simulation (LES). The curved cylinder leads to different flow regimes along the span, which shows the three-dimensionality of the wake field. At a Reynolds number of 100, the shedding was suppressed after flow angle of 135°, and oblique flow was observed at 90°. At a Reynolds number of 500, vortex dislocation was detected at 90° and 135°. These observations are in good agreement with the three-dimensionality of the wake field that arose due to the curved shape.

• 지질공학
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• 제27권3호
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• pp.191-205
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• 2017

본 연구에서는 불투과형 사방댐과 링네트에 가해지는 충격하중을 평가하기 위해 토석류 모형축소실험을 수행하였다. 실험 결과, 토석류는 유체와 유사한 거동을 함에 따라 불투과형 사방댐 배면에 가해지는 토석류 충격하중은 하부구간이 4.14 kN로 가장 높게 작용하며 중간, 상부구간이 3.66 kN, 1.66 kN 가해지는 것으로 측정되었다. 링네트 실험결과 또한 불투과형 사방댐 결과와 같이 충격하중은 하부구간이 크며 상부로 갈수록 감소하는 경향을 보인다(2.28 kN, 1.95 kN, 1.49 kN). 수치해석 결과를 이용하여 토석류 흐름에 의한 토석류 방지시설 충격하중 흡수메커니즘을 분석한 결과, 불투과형 사방댐은 콘크리트 옹벽과 같이 구조물 자체의 강성을 이용하여 수평력에 저항하므로 실제 구조물에 작용한 수평력은 이론식과 유사한 결과가 제시되는 반면, 링네트는 강연선 탄성늘음과 네트 전면으로의 입자 투과를 이용하므로 충격하중은 사방댐 결과보다 최대 45% 감소하는 결과가 제시되었다.

• 한국항공우주학회지
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• 제40권9호
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• pp.745-751
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• 2012

하이브리드 로켓은 축 방향의 산화제 유동과 고체 연료의 기화로 인한 벽면 분출 유동사이의 상호 간섭에 의해 복잡한 형태의 혼합 전단층이 존재한다. 연소실 입구에 링이 설치되어 있고 질량분사가 있는 실린더 유동에 대하여 압축성 효과를 고려한 LES(Large Eddy Simulation) 기법을 적용하여 수치계산을 수행하였다. 최근의 실험에 의하면 연료 중간에 링과 같은 다이아프램이 설치된 경우, 연소율의 증가가 관찰되었다. 계산 결과에 따르면, 축방향 유동과 벽면 분출 유동이 상호 간섭하여 발생하는 벽면 와류가 국부적인 연료 표면으로의 열전달을 증가시켜 실험에서 관찰되는 딤플이 생성되는 것을 확인하였다. 또한 연소실 입구에 설치된 링에 의하여 발생되는 와류는 벽면 와류가 보다 활발하게 생성되고 열전달과 혼합을 향상시키는 역할을 하며 이 때문에 연소율이 증가되는 것으로 보인다.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.26-29
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• 2004

In this paper, we report the numerical and experimental solutions of the dynamic characteristics of a vortex ring in a circular cylinder generated by impinging a fluid blob from a hole on the bottom wall of the cylinder. We managed to visualize successfully the flow pattern shown on the vertical and horizontal planes by using a specially designed optical apparatus. Results of three-dimensional computation for the flow are shown to be in a satisfactory agreement with the experimental ones. We also report the experimental results which show a breaking of the axi-symmetric pattern after the vortex touches the free surface.

• 한국정밀공학회지
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• 제11권5호
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• pp.134-142
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• 1994

An upper bound elemental technique (UBET) is applied to predict variations of neutral plane and optimal position of the initial billet for rib-wep shaped ring forging. In the analysis, the neutral plane position and velocity fields are determined by minimizing the total power consump- tion with respect to chosen parameters. The degree of die-cavity filling by initial billet-position and the variations of neutral plane by friction condition are investigated. Experiments have been carried out with pure plasticine billets at room temperature. The theoretical predictions of the forging load and the flow pattern are in good agrement with the experimental results.

• Tribology and Lubricants
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• 제24권3호
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• pp.140-146
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• 2008

The floating ring seal which is used in the high pressure turbo pump is frequently used in the oxidizer pump and the fuel pump of the turbo pump of the liquid propulsion rocket, because it is able to minimize clearance to decrease the leakage flow rate. But, the floating ring seal has a tendency to increase instability in decreasing eccentricity ratio. To complement this weakness, it is devised bump floating ring seal which is inserted bump in the outer surface. It has various experiment results. But the theoretical study of the bump floating ring seal didn't investigated yet. In this paper, we analyse about static characteristics of bump floating ring seal, compared previous experimental results. To analyze the characteristic of bump floating ring seal, we coupled perturbation method of floating ring seal and FEM of bump foil.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.194-194
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• 2008

• 한국자동차공학회논문집
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• 제8권5호
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• pp.105-113
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• 2000

In order to clarify the final process of oil consumption, the distribution and flow of oil through each ring were visualized by induced fluorescence method. Motoring and firing test were performed in a single cylinder research engine with transparent cylinder liner. The appropriate calibration techniques were used to solve the unstability of induced light intensity as well as to know the relation of the oil film thickness and output signal. Oil behavior was also observed at dynamic state by high speed CCD camera. By analyzing the oil film thickness converted from the photographed image, it was observed that the main route of oil transport through each ring is the end gap under the usual operating condition, low engine speed and low load condition. Oil film thickness is observed to be irregular and tend to move in a body horizontally at a given piston land. And it is also found that oil flows through oil ring gap so quickly that it can be observed in a single cycle, but it flows so slowly through top and 2nd compression rings that it takes quite a long time to detect the flow.