• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.419-424
• /
• 2001

This paper deals with the development of a new method that can obtain heat transfer coefficient and reference tree stream temperature simultaneously. The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is shown how the uncertainties in heat transfer coefficient and tree stream temperature can be reduced. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.

• 대한기계학회논문집B
• /
• 제26권10호
• /
• pp.1465-1471
• /
• 2002

This paper deals with the development of a new method that can obtain the heat transfer coefficient and the reference free stream temperature simultaneously. The method is experimentally verified through comparison with results in convective heat transfer experiments of a circular impinging jet using two narrow-band TLCs. The general method described in this paper is highly recommended to many heat transfer models with the unknown or ambiguous free stream temperature.

• 대한기계학회논문집B
• /
• 제26권12호
• /
• pp.1707-1714
• /
• 2002

This paper deals with the development of a new method that can obtain heat transfer coefficient and reference free stream temperature simultaneously, The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is found that the errors could be reduced more than 2 times less. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.

• 대한기계학회논문집
• /
• 제15권6호
• /
• pp.2062-2072
• /
• 1991

본 연구에서는 역류의 측정과 원주의 근접 후류의 난류 구조에 미치는 자유흐 름 난류의 영향을 정성적 및 정량적으로 조사하기 위하여, 역류가 존재할 경우나 순간 유입각이 매우 큰 경우에도 난류의 측정이 가능한 split film probe(이하 SFP로 줄여 표기함)를 사용하여 평균 유동장과 난류의 2차 및 3차 모멘트의 변화, 속도 변동 상관 의 변화 및 대규모 와류의 유출 주파수 특성 등을 측정 분석하여, 격자에 의해 형성된 서로 다른 자유흐름 난류특성에 따른 실험 결과들을 비교 검토 해보고자 한다.

• 한국전산유체공학회지
• /
• 제14권4호
• /
• pp.67-77
• /
• 2009

This paper is a continuation of a recent development on the Hermite-based divergence-free element method and deals with a non-isothermal fluid flow driven by the buoyancy force in a square cavity with temperature difference across the two sides. Two Hermite functions are considered for numerical computations in this paper. One is a cubic function and the other is a quartic function. The degrees-of-freedom of the cubic Hermite function are stream function and its first and second derivatives for the velocity field, and temperature and its first derivatives for the temperature field. The degrees-of-freedom of the quartic Hermite function include two second derivatives and one cross derivative of the stream function in addition to the degrees-of-freedom of the cubic stream function. This paper presents a brief review on the Hermite based divergence-free basis functions and its finite element formulations for the buoyancy driven flow. The present algorithm does not employ any upwinding or a stabilization term. However, numerical values and contour graphs for major flow variables showed good agreements with those by De Vahl Davis[6].

• International Journal of Aeronautical and Space Sciences
• /
• 제18권2호
• /
• pp.279-289
• /
• 2017

In this study, a series of conjugate heat transfer (CHT) analyses are conducted for a stage of a fully cooled high-pressure turbine (HPT) at elevated levels of free stream turbulence (Tu = 5% and 25.7%). The goal of the analyses is to investigate the influence of high turbulence intensity on the fluid-thermal characteristics of a nozzle guide vane (NGV). The turbine inlet temperature is defined by considering a typical radial temperature distribution factor (RTDF). The Unsteady Reynolds Average Navier-Stokes (URANS) CHT simulations are carried out using CFX 15.0, a commercial CFD package. The presented CFD modeling approach for high turbulence intensity is verified with the experimental data from two types of NASA C3X NGVs with films. The computation grid is generated for both the fluid and solid domains. The fluid domain grid is created using a tetrahedral grid system with prism layers because of its complex geometry, and the solid domain grid is composed of only tetrahedral elements. The analytical results are compared to understand the effect of turbulence on flow characteristics and metal temperature distributions. The results obtained in this study provide useful insights on the effects of high free stream turbulence and unsteadiness. The results also lead to the proposal of meaningful turbine design guidelines.

• 한국물환경학회지
• /
• 제34권1호
• /
• pp.96-108
• /
• 2018

Large efforts have recently been made on research and development of sustainable and energy-efficient short-cut nitrogen removal processes owing to strong attention to the energy neutral/positive wastewater treatment system. Anaerobic ammonium oxidizing bacteria (anammox bacteria) have been highlighted since 1990's due to their unique advantages including 60% less energy consumption, nearly 100% reduction for carbon source requirement, and 80% less sludge production. Side-stream short-cut nitrogen removal using anammox bacteria and partial nitritation anammox (PN/A) has been well established, whereas substantial challenges remain to be addressed mainly due to undesired main-stream conditions for anammox bacteria. These include low temperature, low concentrations of ammonia, nitrite, free ammonia, free nitrous acid or a combination of those. In addition, an anammox side-stream nitrogen management is insufficient to reduce overall energy consumption for energy-neutral or energy positive water resource recovery facility (WRRF) and at the same time to comply with nitrogen discharge regulation. This implies the development of the successful main-stream anammox based technology will accelerate a conversion of current wastewater treatment plants to sustainable water and energy recovery facility. This study discusses the status of the research, key mechanisms & interactions of the protagonists in the main-stream PN/A, and control parameters and major challenges in process development.

• 한국항공우주학회지
• /
• 제45권4호
• /
• pp.342-348
• /
• 2017

본 연구에서는 초음속 주유동 환경에서의 막냉각 특성에 대해 적외선 열상법을 적용한 시험을 수행하였다. 막냉각 시험은 수축형 막냉각 노즐을 갖는 쐐기형 막냉각 시편을 이용해 마하수 3.0, 단위 길이 당 레이놀즈수 $42.53{\times}10^6$ 와 $69.35{\times}10^6$ 인 조건을 구현한 자유-제트 시험 설비에서 수행하였다. 모사 탐색창에 해당하는 PEEK의 표면 온도를 계측하여 막냉각 효율을 산출하였고 받음각 및 분사율이 막냉각 효율에 미치는 영향을 분석하였다. 막냉각을 적용하지 않는 경우와 비교할 때, 막냉각을 적용할 경우 측정된 PEEK의 표면 온도가 크게 감소하였다. 막냉각의 유용성은 시간에 따른 PEEK의 표면 온도로부터 산출한 열유속 특성으로도 확인할 수 있다. 분사율이 증가할수록 보호되는 PEEK의 영역이 주유동과 막냉각 유동의 흐름 방향으로 확장되었다.

• 대한기계학회논문집B
• /
• 제23권5호
• /
• pp.567-576
• /
• 1999

An experimental study has been conducted to investigate the effects of the free stream turbulence intensity and Reynolds number on the heat transfer and flow characteristics In the linear turbine cascade. Profiles of the time-averaged velocity, turbulence intensity, and Reynolds stress were measured in the turbine cascade passage. The static pressure and heat transfer distributions on the blade suction and pressure surfaces were also measured. The experiments were made for the Reynolds number based on the chord length, Rec = $2.2{\times}10^4$ to $1.1{\times}10^5$ and the free stream turbulence intensity, $FSTI_1$ = 0.6% to 9.1 %. The uniform heat flux boundary condition on the blade surface was created using the gold film Intrex and the surface temperature was measured by liquid crystal, while hot wire probes were used for the flow measurements. The results show that the free stream turbulence promotes the boundary layer development and delays the flow separation point on the suction surface. It was found that the boundary layer flows on the suction surface for all Reynolds numbers tested with $FSTI_1$ = 0.6% are laminar. It was also found that the heat transfer coefficient on the blade surface increases as the free stream turbulence intensity increases and the flow separation point moves downstream with an increasing Reynolds number. The results of skin friction coefficients are in good agreement with the heat transfer results in that for $FSTI_1{\geq}2.6%$, the turbulent boundary layer separation occurs.

• 한국안전학회지
• /
• 제9권1호
• /
• pp.146-154
• /
• 1994

A series of numerical calculations are performed in order to investigate the dispersion mechanism of toxic gaseous and solid pollutants in extremely short-term and short range. The calculations are carried out in an open space characterized by turbulent boundary layer. The simulation is made by the use of numerical model, in which a control-volume based finite difference method is used together with the SIMPLEC algorithm for the resolution of the pressure-velocity coupling problem. The Reynolds stresses are solved by two-equation, k-$\varepsilon$ model modified for buoyancy. The major parameters consider-ed in this study are temperature, velocity and Injection height of toxic gases, environmental conditions such as temperature and velocity of free stream air, and topographic factor. The results are presented and discussed in detail. The flow field is commonly characterized by the formation of a strong recirculation zone due to the upward motion of the hot toxic gas and ground shear stress. The driving force of the upward motion is explained by the effect of thermal buoyancy of hot gas and the difference of inlet velocity between toxic gas and free stream.