• 대한기계학회논문집B
• /
• 제27권12호
• /
• pp.1655-1666
• /
• 2003

It is experimentally well-known that high anisotropies of the turbulent flow field are dominant inside the tip leakage vortex, which is attributable to a substantial proportion of the total loss and constitutes one of the dominant mechanisms of the noise generation. This anisotropic nature of turbulence invalidates the use of the conventional isotropic eddy viscosity turbulence models based on the Boussinesq assumption. In this study, to check whether an anisotropic turbulence model is superior to the isotropic ones or not, the results obtained from the steady-state Reynolds averaged Navier-Stokes simulations based on the RNG k-$\varepsilon$ model and the Reynolds stress model (RSM) are compared with experimental data for two test cases: a linear compressor cascade and a forward-swept axial-flow fan. Through this comparative study of turbulence models, it is clearly shown that the RSM, which can express the production term and body-force term induced by system rotation without introducing any modeling, should be used to predict quantitatively the complex tip leakage flow, especially in the rotating environment.

• 대한기계학회논문집B
• /
• 제27권1호
• /
• pp.84-94
• /
• 2003

It is known that tip clearance flows reduce the pressure rise, flow range and efficiency of the turbomachinery. So, the clear understanding about flow fields in the tip region is needed to efficiently design the turbomachinery. The Navier-Stokes code with the proper treatment of the boundary conditions has been developed to analyze the three-dimensional steady viscous flow fields in the transonic rotating blades and a numerical study has been conducted to investigate the detail flow physics in the tip region of transonic rotor, NASA Rotor 67. The computational results in the tip region of transonic rotors show the leakage vortices, leakage flow from pressure side to suction side and their interaction with a shock. Depen ding on the operating conditions, toad distributions and the position of shock-wave on the blade surface are very different close to the blade tip of the transonic compressor rotor. The load distribution and the shock-wave position close to the blade tip had the close relationship with the starting position of leakage vortex and the direction of leakage flow.

• 한국자동차공학회논문집
• /
• 제15권5호
• /
• pp.63-71
• /
• 2007

The conversion efficiency, durability and pressure drop of the automotive exhaust catalysts are dependent on the flow distribution within the substrate. Conventional porous medium approaches assuming monolith resistance based on the one-dimensional laminar flow for simulating the flow through the automotive exhaust catalysts over-predict the flow uniformity in the monolith. In this study, additional pressure loss is also considered by accounting for entrance effects due to the oblique flow incident on the front face of monolith as a consequence of flow separation and recirculation within the diffuser. The incorporation of an additional pressure loss improves the predictions for the maximum flow velocity within the substrate. An numerical study has also been conducted for the three-dimensional unsteady incompressible non-reacting flow inside various dual-monolith catalytic converters for the rapid acceleration/deceleration driving.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2011년도 제37회 추계학술대회논문집
• /
• pp.830-834
• /
• 2011

본 연구에서는 액체로켓엔진의 터보펌프용 초음속 터빈 로터 블레이드에 스윕 각도 ${\pm}15^{\circ}$를 적용하여 전방스윕(FSW), 후방스윕(BSW)모델의 유동형태 및 성능을 기준모델(NSW)과 비교하여 스윕 적용의 효과를 살펴보았다. 3차원 Navier-Stokes 유동해석에는 상용 코드인 FLUENT 6.3 Parallel을 사용하였다. BSW 모델은 기준 모델(NSW)에 비해 팁 간극으로 빠져나가는 누설 손실량을 줄이는데 효과가 있었고 정효율 증가에도 영향을 미쳤다.

• 한국터널지하공간학회 논문집
• /
• 제9권4호
• /
• pp.361-375
• /
• 2007

본 논문에서는 터널시공시 지하수 저하를 동반하는 시공조건에서 발생하는 지표침하 특성에 관한 연구내용을 다루었다. 이를 위해 먼저 지하수 저하로 인한 지반침하 문제에 대한 국내외 기존 연구내용을 살펴보았으며, 지하수 유동시 응력-간극수압 상호작용이 고려된 유한요소해석 모델을 구축하고 이론적 검증을 통해 유한요소해석 모델의 타당성을 검토하였다. 구축된 유한요소해석 모델을 토대로 다양한 시공조건에 대한 매개변수 연구를 수행하고 그 결과를 토대로 지하수 유동시 지반침하에 영향을 미치는 주요 인자를 검토하였으며, 아울러 터널시공이 지하수 저하를 동반하는 시공조건에서의 지표침하 특성을 기존의 이론과 연계하여 고찰하였다.

• 대한기계학회논문집
• /
• 제16권4호
• /
• pp.795-802
• /
• 1992

본 연구에서는 일정한 각도의 분사를 갖는 평씨일(plain seal)에 대하여 각 인자들이 누수성능에 미치는 영향을 수치적으로 조사하였다. 인자들로는 축방향 레 이놀즈수, 축회전속도, 분사의 유입속도, 간극비, 분사의 위치 및 유입각 등이 고려되 었다.

• 대한기계학회논문집B
• /
• 제27권7호
• /
• pp.883-892
• /
• 2003

The experiment using three-dimensional laser Dopperr velocimetery (LDV) measurements and the computation using the Reynolds stress model of the commercial code, FLUENT, were conducted to give a clear understanding on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition. The tip leakage vortex was generated near the position of the minimum wall static pressure, which was located at approximately 12% chord downstream from the leading edge of blade suction side, and developed along the centerline of the pressure trough within the blade passages. A reverse flow between the blade tip region and the casing, induced by tip leakage vortex, acted as a blockage on the through-flow. As a result, high momentum flux was observed below the tip leakage vortex. As the tip leakage vortex proceeded to the aft part of the blade passage, the strength of tip leakage vortex decreased due to the strong interaction with the through-flow and casing boundary layer, and the diffusion of tip leakage vortex caused by high turbulence. In comparison with LDV measurement data, the computed results predicted the complex viscous flow patterns inside the tip region, including the locus of tip leakage vortex center, in a reliable level.

• 대한기계학회논문집B
• /
• 제28권5호
• /
• pp.535-544
• /
• 2004

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s : 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s : 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2010년도 제39회 하계학술대회 초록집
• /
• pp.92-92
• /
• 2010

전북대학교에서는 우리나라 최초로 0.4 및 2.4 MW 급 초음속 열플라즈마 시험 시설 구축사업을 진행하고 있으며, 이를 이용한 응용 분야 별 선행연구를 수행하고 있다. 구축 시험 시설의 핵심장치인 MW 급 대출력 초음속 열플라즈마 발생기로는 양극과 음극 사이에, 전기적으로 절연된 도넛 형태의 간극을 다수 삽입하여 아크 길이를 늘림으로써, 플라즈마 출력을 비례하여 높일 수 있는 Segmented 형 아크 직류 토치를 사용하고자 하며, 제작을 위해 설계 중인 토치는 0.4 및 2.4 MW 출력에 대해, 마하 2 이상의 초음속 유동에서 각각 13 및 20 MJ/kg 이상의 플라즈마 비엔탈피 구현을 목표로 하고 있다. 특히, 이와 같은 고엔탈피 초음속 유동의 달성은 0.4MW 급의 경우엔 공기유량 0.01 kg/s 이상에서, 2.4 MW 급의 경우엔 0.05 kg/s 이상에서 10Torr 이하의 진공과 투입된 MW 규모의 열량을 지속적으로 유지 및 제거할 수 있는 시설이 있어야 구현 가능하므로 이를 위한 건축과 지원시설 구축을 동시에 진행하고 있다. 본 발표에서는 0.4 MW 급 초음속 열플라즈마 시험 시설을 중심으로, 상기 MW 급 Segmented 형 아크 직류토치와 이를 구동하기 위한 대출력 초음속 열플라즈마 시험 시설에 대해 그 동안 전북대학교에서 진행되어 온 개념설계 내용을 소개하고자 한다. 덧붙여, 최근 본 사업단에서 선행 연구 중인 고엔탈피 초음속 열플라즈마 진단 계측 기법과 향후 응용분야 및 핵심 연구개발 과제 등에 대한 간략한 소개도 함께 하고자 한다.

• 한국자동차공학회논문집
• /
• 제23권2호
• /
• pp.191-198
• /
• 2015

In this study, the flow characteristics at the ventilation holes was analyzed by using numerical method when carbon composite brake disk was rotated at a constant speed. In order to ensure the validity of the analysis results, grid dependency test was performed by considering the accuracy and appropriateness, and 4mm mesh size was selected for decrease of the maximum error rate 63.6%. As a result, the outside air flows in the clearance between the disk and shaft in case of B model. whereas, the outside air flows in the clearance or the outlet of the ventilation holes in case of A and C models. And also average static pressure at the outlet was changed depending on shape of the ventilation holes and rotational speed of the disk in case of A and C models. Besides, in the B model, intake air according to the clearance goes with side surface of ventilation hole, and so increased by mean velocity of 4.64m/s and mean pressure of 0.58pa in the ventilation hole outlet, in case of disk rotational speed of 146.21rad/s.