• Title/Summary/Keyword: Similarity Solution

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Instability Analysis of Natural Convection Flow along Isothermal Vertical Cylindrical Surfaces (등온 수직 원통표면을 연하여 흐르는 자연대류 유동의 파형 불안정성)

  • 유정열;윤준원;노승탁
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.1
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    • pp.161-169
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    • 1989
  • A stability problem on wave instability of natural convection flow along isothermal vertical cylindrical surfaces has been formulated, accounting for the non-parallelism of the basic flow and thermal fields. Then the problem is solved numerically under the simplifying assumption of the parallelism of the basic flow quantities. It is shown that the flow corresponding to the same characteristic boundary layer thickness becomes more stable as the value of the curvature parameter increases. The stability characteristics for Pr=0.7 appear to be more sensitive to the curvature parameter than those for Pr=7.

The Effect of Heat Conduction resistance on Laminar Film Condensation along a Horizontal Plate (수평평판의 막응축에서 전도 열저항의 영향)

  • Lee, Euk-Soo
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • pp.183-188
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    • 2005
  • The effect of heat conduction resistance on laminar film condensation of the pure saturated vapor in forced flow over a flat plate has been investigated as boundary layer solutions. A efficient numerical methods for water are proposed for its solution. The momentum and energy balance equations are reduced to a nonlinear system of ordinary differential equations with four parameters: the Prandtl number, Pr, Modified Jacob number, $Ja^{\ast}/Pr$, defined by an overall temperature difference, a property ratio $\sqrt{P_l{\mu}_l/P_v{\mu}_v}$ and the conjugate parameter ${\zeta}$. The similarity and simplified solutions obtained reveal the effects of the conjugate parameter.

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Numerical Simulation of Slamming Phenomena for 2-D Wedges (2차원 쐐기형 구조물의 슬래밍 현상에 대한 수치 유동해석)

  • Yum, Deuk-Joon;Yoon, Bum-Sang
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.5
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    • pp.477-486
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    • 2008
  • Numerical analysis for slamming impact phenomena has been carried out when 2-dimensional wedge shaped structure with finite deadrise angles enter the free surface by using a commertial CFD code, FLUENT. Fluid is assumed incompressible and entry speed of the structure is kept constant. Geo-reconstruct scheme (or PLIC-VOF scheme) is used for the tracking of the deforming free surface. User defined function of 6 degrees of freedom motion and moving dynamic mesh option are used for the expression of the downward motion of the structure and deforming of unstructured meshes adjacent to the structure. The magnitude and the location of impact pressure and the total drag force which is the summation of pressures distributed at the bottom of the structure are analyzed. Results of the analysis show good agreement with the results of similarity solution, asymptotic solution and the solution of BEM.

A Study on the Thermal Boundary Layer Flow of a Micropolar Fluid in the Vicinity of a Wedge (미세극성 유체 유동장에 놓여진 쐐기형 물체주위의 열경계층에 관한 연구)

  • 김윤제
    • The Korean Journal of Rheology
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    • v.11 no.2
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    • pp.122-127
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    • 1999
  • The characteristics of thermal boundary layer flow of a micropolar fluid in the vicinity of a wedge has been studied with constant surface temperature. The similarity variables found by Falkner and Skan are employed to reduce the streamwise-dependence in the coupled nonlinear boundary layer equations. Numerical solutions are presented for the heat transfer characteristics with Pr=1 using the fourth-order Runge-Kutta method and their dependence on the material parameters is discussed. The distributions of dimensionless temperature and Nusselt number across the boundary layer are compared with the corresponding flow problems for a Newtonian fluid over wedges. Numerical results show that for a constant wedge angle with a given Prandtl number, Pr=1, the effect of increasing values of K results in an increasing thermal boundary thickness for a micropolar fluid, as compared with a Newtonian fluid. For the case of the constant material parameter K, however, the heat transfer rate for a micropolar fluid is lower than that of a Newtonian fluid.

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Numerical Experimentations on Flow Impact Phenomena for 2-D Wedge Entry Problem (2차원 쐐기형 구조물 입수 시 발생하는 유체 충격 현상에 대한 수치 실험적 연구)

  • Yum, Duek-Joon;Du, Hun;Kim, Young-Chul
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.12 no.8
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    • pp.3374-3383
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    • 2011
  • In this study, numerical analyses for slamming impact phenomena have been carried out using a 2-dimensional wedge shaped structure having finite deadrise angles. Fluid is assumed incompressible and entry speed of the structure is kept constant. Geo-reconstruct(or PLIC-VOF) scheme is used for the tracking of the deforming free surface. Numerical analyses are carried out for the deadrise angles of $10^{\circ}$, $20^{\circ}$ and $30^{\circ}$. For each deadrise angle, variations are made for the grid size on the wedge bottom and for the entry speed. The magnitude and the location of impact pressure and the total drag force, which is the summation of pressure distributed at the bottom of the structure, are analyzed. Results of the analyses are compared with the results of the Dobrovol'skaya similarity solutions, the asymptotic solution based on the Wagner method and the solution of Boundary Element Method(BEM).

INTERACTION OF SUPERNOVA REMNANTS WITH STELLAR-WIND BUBBLES (초신성 잔해와 항성풍 공동간의 상호 작용)

  • Lee, Jae-Kwan;Koo, Bon-Chul
    • Publications of The Korean Astronomical Society
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    • v.12 no.1
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    • pp.111-143
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    • 1997
  • We have developed a spherical FCT code in order to simulate the interaction of supernova remnants with stellar wind bubbles. We assume that the density profile of the supernova ejecta follows the Chevalier mode1(1982) where the outer portion has a power-law density distribution($\rho{\propto}\gamma^{-n}$) and the SN ejecta has a kinetic energy of $10^{51}$ ergs. The structure of wind bubble has been calculated with the stellar mass loss rate $\dot{M}=5\times10^{-6}M_{\odot}/yr$ and the wind velocity $\upsilon=2\times10^3$ km/s We have simulated seven models with different initial conditions In the first two models we computed the evolution of SNRs with n=7 and n=14 in the uniform medium The numerical results agree with the Chevalier's similarity solution at early times. When all of the power-law portion of the ejecta is swept up by the reverse shock, the evolution slowly converges to the Sedov-Taylor stage. There is not much difference between the two cases with different n's The other five models simulate SNRs produced inside wind bubbles. In model III, we consider the SN ejecta of 1.4 $M_{\odot}$ and the radius of bubble ~2.76 pc so that ratio of the mass $\alpha(=M_{W.S}/M_{ej}$ is 2. We follow the complex hydrodynamic flows produced by the interaction of SN shocks with stellar shocks and with the contact discontinuities, In the model III, the time scale for the SN shock to cross the wind shell $\tau_{cross}$ is similar to the time scale for the reverse shock to sweep the power-law density profile $\tau_{bend}$. Hence the SN shock crosses the wind shell. At late times SN shock produces another shell in the ambient medium so that we have a SNR with double shell structure. From the numerical results of the remaining models, we have found that when $\tau_{cross}/\tau_{bend}\leq2$, or equivalently when $\alpha\leq50$, the SNRs produced inside wind bubbles have double shell structure. Otherwise, either the SN shock does not cross the wind shell or even if it crosses at one time, the reverse shock reflected at the center accelerates the wind shell to merge into the SN shock Our results confirm the conclusion of Tenorio-Tagle et a1(1990).

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