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Oldroyd B 유체의 평면 수축 유동에 관한 수치 해석적 연구
유정열,나양,Yoo, Jung-Yul,Na, Yang 한국유변학회 1990 Korea-Australia rheology journal Vol.2 No.1
This study analyzes the planar 4:1 contraction flow of viscoelastic fluids with retardation time using finite volume method. To consider separately the elasticity effect of the viscoelastic fluid without shear thinn-ing effect, Oldroyd B liquid model is adopted for the numerical simulation. Instead of the stream function-vorticity formulation, SIMPLER algorithm with staggered grid system which incorporates primitive variable has been introduced in discretizing the momentum equations. An upwind corrected scheme has been used in discetizing the constitutive equations for the non-Newtonian part of the stress. The size of the corner vortex is shown to be slightly influenced by the Weissenberg number. However as the Weissenberg number is increased the chang-ing of the vortex shape agrees qualitatively well with some experimental studies.
정정열(Jung-Yeul Jung),유정열(Jung Yul Yoo) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
In this study, the mechanism of enhanced thermal conductivity is elucidated on the bases of both electric double layer (EDL) and kinetic theory. A novel expression for the thermal conductivity of nanofluids is proposed and verified by applying to Al₂O₃ nanofluids with regard to various temperatures, volume fractions and particle sizes. In dilute nanofluids, the effects of Brownian motion and particle interaction on enhancing the thermal conductivity of nanofluids are quite comparable while the effect of particle interaction due to EDL is more prominent in dense nanofluids. The model presented in this paper shows that particle interaction due to the electrical double layer is the most responsible for the enhancement of thermal conductivity of nanofluids.
[열유체부문] 유한요소를 이용한 MIRA 모델주위의 유동해석
최형권(Hyounggwon Choi),강성우(Sungwoo Kang),유정열(Jung Yul Yoo) 한국자동차공학회 2001 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2001 No.11_1
A finite element code based on P2PI or PIPI tetra element has been developed for the large eddy simulation (LES) of turbulent flows around a complex geometry. Fractional 4-step algorithm is employed to obtain time accurate solution since it is less expensive than the integrated formulation, in which the velocity and pressure fields are solved at the same time. Crank-Nicolson method is used for second order temporal discretizarion and Galerkin method is adopted for spatial discretization. For very high Reynolds number flows, which would require a fom1idable number of nodes to resolve the flow field, SUPG (Streamline Upwind Petrow-Galerkin) method is applied. As a benchmark problem for code validation. turbulent flows around a sphere and turbulent channel flows<br/> have been studied at various Reynolds numbers. Turbulent flow around MIRA model has been solved using P2PI element and Smagorinsky model at Re= 2.6 x 106. Furthermore, a parallel code based on domain-decomposition method using PIPI element has been developed for LES of turbulent flow and tested with turbulent channel flows. Turbulent flow analysis around MIRA model using the present LES-parallel code is ongoing and will be presented in the near future<br/>
임남혁(Namhyuk Lim),김성욱(Sungwook Kim),유정열(Jung Yul Yoo) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
This paper presents the design, fabrication, and testing of the capillary-induced pressure drop valve,<br/> thermocapillary pumping of liquid droplet in hydrophilic channels and the splitting of droplet. The capillaryinduced<br/> pressure drop is derived with thermodynamic approach considering three-dimensional meniscus<br/> shape which is essential for calculating pressure drop in the diverging shape channel when the aspect ratio is<br/> close to one. The micro channel is fabricated via MEMS processes, which consists of the liquid stop valve to<br/> retard the liquid droplet, thermocapillary pumping region and the bifurcation region. Also the micro heaters<br/> are fabricated to drive the droplet by thermocapillary. The theoretical approaches agree well with the<br/> experimental data. The functionality of capillary valve is confirmed to be valid when the aspect ratio is<br/> smaller than one. To overcome the difficulty in splitting of the droplet due to the pressure drop in the general<br/> Y-shape channel, the protrusion shape is employed for easy splitting in the bifurcation channel.
정정열(Jung-Yeul Jung),유정열(Jung Yul Yoo),김영원(Young Won Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Nano-particles (on the order of 1 to 100 ㎚) contained within the droplet are moved by liquid flow and stacked at the contact line. The self-pinned contact line under the evaporating droplet is very interesting in the field of patterning and separation of particles and biocells<SUP>2-5</SUP>. Models accounting for the nano-particles’ flow and deposit patterns have been reported and verified by various experiments. Here, we report for the first time a phenomenon where micro-particles (on the order of 1 ㎛) in the colloid droplet flow to the center of droplet. There are three modes of fluid and particle flow in the evaporating droplet. In the first mode, a self-pinned contact line is maintained and the fluid and micro/nano-particles flow to the contact line. In the second mode, micro/nano-particles self-assemble at the near contact line, as reported by Jung and Kwak. In the final mode, only micro-particles are advected to the center of the droplet due to movement of the contact line.
밑으로부터 가열되는 평면 Couette 유동에서 점성소산이 열적 불안정성에 미치는 영향
유정열,박영무,Yoo, Jung Yul,Park, Young Moo 대한설비공학회 1988 설비저널 Vol.17 No.4
An analysis has been given for the effect of viscous dissipation on the thermal instability of plane Couette flow between two parallel plates maintained at different constant temperatures. Under the assumption that the principle of the exchange of stabilities holds, stationary disturbance quantities in the form of longitudinal vortices are considered. The magnitudes of disturbance quantities are then represented as fast convergent power series so that the eigenvalue problem for determining the onset conditions of the thermal instability may be reduced to a simplified problem of finding the roots of a $4{\times}4$ determinant. It is shown that as the magnitude of the visucous dissipation increases the flow becomes more susceptible to instabilities, which is in very good agreement with previous results obtained in some related researches.
저레이놀즈수 난류모델을 사용한 정익-동익 상호작용 해석
최창호,유정열,Choi, Chang Ho,Yoo, Jung Yul 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.10
A computational study on unsteady compressible flows has been performed by adopting a low Reynolds number $k-{\omega}$ turbulence model in conjunction with dual time stepping scheme. An explicit four-stage Runge-Kutta scheme for the Navier-Stokes equations and an approximate factorization scheme for the $k-{\omega}$ turbulence model equations are used. Computational results obtained for blade surface pressure distributions in the process of rotor-stator interaction in a turbine stage are in good agreement with extant experimental data. The effects of the wake from the stator on the boundary-layer transition over the rotor blade surface are discussed by showing that high intensity turbulence of the stator wake induces an early transition.
헬리컬 기본교란과 축대칭 분수조화교란을 이용한 원형제트에서의 보텍스 병합 및 제트확산
조성권,유정열,최해천,Cho, Sung Kwon,Yoo, Jung Yul,Choi, Haecheon 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.11
An axisymmetric jet is forced with two helical fundamental waves of identical frequency spinning in opposite directions and an additional axisymmetric sub harmonic wave. The subharmonic component rapidly grows downstream from subharmonic resonance with the fundamental, significantly depending on the initial phase difference. The variations of the subharmonic amplitude with the initial phase difference show cusp-like shapes. The amplification of the sub harmonic results in 'vortex pairing of helical modes'. Furthermore, azimuthal variation of the amplification induces an asymmetric jet cross-section. When the initial subharmonics is imposed with an initial phase difference close to a critical value, the jet-cross section evolves into a three-lobed shape. One lobe is generated by the enhanced vortex pairing and the other two lobes are generated by the delayed vortex pairing. Thus, it is confirmed that the initial phase difference between the fundamental and the subharmonic plays an important role in controlling the jet cross-section.