• 한국유체기계학회 논문집
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• 제11권1호
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• pp.9-17
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• 2008

A numerical study for three-dimensional laminar flow in the entrance region of helical tubes connected with straight ones is carried out to investigate the effects of Reynolds number, pitch and curvature ratio on the oscillation periods of the flow. The fully elliptic governing equations were solved by means of a finite volume method. The fully developed laminar flow boundary condition was applied at the straight tube inlet. This results cover a curvature ratio range of 1/10${\sim}$1/320, a pitch range of 0.0${\sim}$3.2, and a Reynolds number range of 62.5${\sim}$2000. A comparison is made with previous experimental correlations and numerical data. The developments of velocity, local and average friction factors are discussed. The average friction factors are oscillatory in the entrance region of helical pipes. It has been found that the angle required for the flow to be similarly developed is most affected by the curvature ratio. The pitch and Reynolds number do not have any significant effect on the angle. The characteristic angle ${\phi}_c(={\phi}/sqrt{\delta})$, or the characteristic length to diameter ratio $s_c(=l\sqrt{\delta} cos(atan{\lambda})/d)$, can be useful to represent the development of flow in helical tubes. As the pitch increases and as the curvature ratio and Reynolds number decrease, the amplitude and the number of flow oscillations along the main streamwise direction decrease.

• 한국자동차공학회논문집
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• 제11권4호
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• pp.1-6
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• 2003

Steady flow bench test is a practical, powerful and widely used in most engine manufacturers to give a design concept of a new engine. In order to use steady data as a performance index, it is necessary to build some database, which can correlate the port characteristics with engine data. However, it is very difficult to investigate all port shapes with experimental tools. The steady flow scheme is relatively simple and its results are bulk ones such as flow rate and momentum of flow. Therefore a CFD code can be easily applied to the port evaluation. In this study, the steady flow test was simulated through three-dimensional analysis on intake port design for comparing with experimental data and confirming the feasibility of applying analytic method . for this purpose, the effect of valve curvature on flow rate was estimated by a CFD code. Numerical results were compared with those of real steady flow tests. As a result, the results of 3-D analysis were almost consistent with experimental data.

• 한국방재안전학회논문집
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• 제8권1호
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• pp.5-13
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• 2015

본 연구는 수치모형을 이용하여 만곡수로 외측에 설치된 횡월류 위어의 곡률반경에 대한 횡월류 유량계수를 분석한 연구이다. 곡률반경의 변화에 따른 만곡부의 중심각이 $180^{\circ}$인 수로모형을 설계하였으며, FLOW-3D모형에 적용하여 유량계수를 산정하고 직선 수로와 비교하는 방법으로 유량계수의 특성을 분석하였다. 모형의 적용성 검증을 위해 기존에 연구되었던 수리실험과 동일한 조건의 수치모의를 수행하였다. 하폭(b)을 고정시키고 곡률반경($R_c$)을 변화시킴으로써 $R_c/b$의 변화에 따른 유량계수($C_M$)의 변화를 분석하고, 만곡수로의 월류량($Q_{wc}$)에 대한 직선수로의 월류량($Q_{wc}$)의 비를 분석하였다. 분석결과 유량계수는 상류수심, 만곡수로의 곡률반경의 변화에 따라 유량계수는 변화하였으며, 직선과 만곡수로에 대해 분석을 수행하였기 때문에 직선수로의 영향인자를 이용하여 만곡수로에 설치된 횡월류 위어의 월류량과 유량계수를 추정 가능 할 것이라 판단된다.

• 한국자동차공학회논문집
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• 제4권4호
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• pp.118-129
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• 1996

In this study, three dimensional flow analysis in a HVAC duct was performed computationally using various turbulence models and compared numerical predictions such as outlet flow split, surface pressure distribution along the duct to experimental data. It's well known that accuracy of computational predictions of flow heavily dependent on turbulent models and discritization method. Therefore, in this work, to assess the ability of turbulent models to predict characteristics of duct flow, three kinds of models, namely standard $k-\varepsilon$, RNG $k-\varepsilon$ and modified $k-\varepsilon$, containing parameter for the effect of streamline curvature were employed and validated one another by comparing with experimental data. In results, modified $k-\varepsilon$ turbulence model allows a successful prediction of static pressure distribution particulary at around strong curvature but little improvement flow split. In the futrue, adoption of CFD to design HVAC duct with modified $k-\varepsilon$ model will bring benefits of producing more accurate prediction, and also give designers more detail information much more than now.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
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• pp.177-186
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• 2006

Flame surface area is a critical parameter determining turbulent flame speed. Three-dimensionaldirect numerical simulations (DNS) were conducted to figure out the evolution process of flame surface area. Fully compressible Navier-Stokes equations are solved to reproduce premixed flame embedded in isotropic decaying turbulent flow. The tangential straining and curvature of propagating surface affect development of flame area. In this study, four different turbulent intensity flows and three different Le number flames are investigated to force changes in straining and curvature effects. Consistent results are obtained for the probability density functions (PDF) of strain and curvature with previous researches. It is revealed that displacement speed, which is a speed of flame surface relative to unburnt flow, controls the balance between sink and source of flame surface area.

• 한국연소학회지
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• 제12권2호
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• pp.10-19
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• 2007

Flame surface area is a critical parameter determining turbulent flame speed. Three-dimensional direct numerical simulations(DNS) were conducted to figure out the evolution process of flame surface area. Fully compressible Navier-Stokes equations are solved to reproduce premixed flame embedded in isotropic decaying turbulent flow. The tangential straining and curvature of propagating surface affect development of flame area. In this study, four different turbulent intensity flows and three different Le number flames are investigated to force changes in straining and curvature effects. Consistent results are obtained for the probability density functions (PDF) of strain and curvature with previous researches. It is revealed that displacement speed, which is a speed of flame surface relative to unburnt flow, controls the balance between sink and source of flame surface area.

• International Journal of CAD/CAM
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• 제9권1호
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• pp.103-109
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• 2010

Recently, various conformal geometric methods have been presented for non-rigid surface matching and registration. This work proposes to improve the robustness of conformal geometric methods to the boundaries by incorporating the symmetric information of the input surface. We presented two symmetric conformal mapping methods, which are based on solving Riemann-Cauchy equation and curvature flow respectively. Experimental results on geometric data acquired from real life demonstrate that the symmetric conformal mapping is insensitive to the boundary occlusions. The method outperforms all the others in terms of robustness. The method has the potential to be generalized to high genus surfaces using hyperbolic curvature flow.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1998년도 제17회 KOSCI SYMPOSIUM 논문집
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• pp.91-101
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• 1998

The effect of secondary flow on both methane/air and propane/air premixed flame was investigated experimentally. By changing the radius of curvature, various flame behavior was observed. In the V-bend nozzles, flame surface is deformed from axisymmetry. As the exit velocity increased, flame lifted off partially. When the radius of curvature of the V-bend increased, the region where premixed flame is entirely on the rim increased. Since the axial velocity field is changed due to the secondary flow effect, comparison of V-bend and straight tube with the same diameter shows larger V-bend nozzle exit velocity for both flash back and flame blowout. The flame characteristics are mapped with a equivalence ratio, a velocity, and a nozzle radius of curvature. To identify physical reasoning on the flame surface deformation, numerical calculations are conducted. OH radical distributions in flames are visualized by PLIF technique.

• Korean Journal of Mathematics
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• 제29권2호
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• pp.445-453
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• 2021

The purpose of the paper is to study of Para-Kenmotsu metric as a 𝜂-Ricci soliton. The paper is organized as follows: • If an 𝜂-Einstein para-Kenmotsu metric represents an 𝜂-Ricci soliton with flow vector field V, then it is Einstein with constant scalar curvature r = -2n(2n + 1). • If a para-Kenmotsu metric g represents an 𝜂-Ricci soliton with the flow vector field V being an infinitesimal paracontact transformation, then V is strict and the manifold is an Einstein manifold with constant scalar curvature r = -2n(2n + 1). • If a para-Kenmotsu metric g represents an 𝜂-Ricci soliton with non-zero flow vector field V being collinear with 𝜉, then the manifold is an Einstein manifold with constant scalar curvature r = -2n(2n + 1). Finally, we cited few examples to illustrate the results obtained.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.55-65
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• 1998

A numerical and experimental study of three-dimensional steady incompressible non-reacting flow inside various dual-monolith catalytic converters has been conducted for achievement of performance improvement, reduction of light-off time and longer service life by improving the flow uniformity within the monolith. In this study, the effects of curvature of inlet exhaust pipe and monolith brick length on the flow uniformity and pressure drop within monolith were numerically investigated. The computations are confirmed by measurements of steady flow. The agreement between computations and experiment was relatively good. The result of this study shows that curvature of inlet exhaust pipe and monolith brick length gave a great effect on the flow uniformity and the shorter the brick length, the lower flow uniformity and the less pressure drop.