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리광훈,성형진,Rhee, Gwang-Hoon,Sung, Hyung-Jin 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.3
An unsteady numerical simulation was performed for locally-forced separated and reattaching flow over a backward-facing step. The local forcing was given to the separated and reattaching flow by means of a sinusoidally oscillating jet from a separation line. A version of the $k-{\varepsilon}-f_{\mu}$ model was employed, in which the near-wall behavior without reference to distance and the nonequilibrium effect in the recirculation region were incorporated. The Reynolds number based on the step height (H) was fixed at $Re_H=33000$, and the forcing frequency was varied in the range $0{\leq}St_H{\leq}2$. The predicted results were compared and validated with the experimental data of Chun and Sung. It was shown that the unsteady locally-forced separated and reattaching flows are predicted reasonably well with the $k-{\varepsilon}-f_{\mu}$ model. To characterize the large-scale vortex evolution due to the local forcing, numerical flow visualizations were carried out.
직접수치모사를 이용한 공간발달하는 난류경계층에서의 표면조도의 영향
성형진(Hyung Jin Sung),이승현(Seung-Hyun Lee) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
The effects of surface roughness on a spatially developing turbulent boundary layer were investigated by comparing direct numerical simulations over rough and smooth walls. The Reynolds number based on the momentum thickness is Re<SUB>θ</SUB>?300~1400. The roughness is composed of periodically arranged two-dimensional spanwise rods and roughness height is k=1.5θ<SUB>in</SUB>, which corresponds to k/δ?0.045~0.125. Using very large domain along the streamwise direction, spatially developing characteristics of roughness effects in the outer layer are observed. Along the downstream, the wall friction velocity approaches to a constant value and the similarity profiles of turbulent stresses could be obtained. The roughness effects of turbulent stresses in the outer layer were more pronounced along the downstream. This investigation shows that the roughness effects on turbulent stresses are not restricted to the roughness sublayer but are felt throughout the boundary layer.
Polydimethylsiloxane 기반 미세유체시스템의 음향열적 가열 및 응용
성형진(Hyung Jin Sung),하병항(Byunghang Ha),박진수(Jinsoo Park),굴람 데스트기르(Ghulam Destgeer),정진호(Jin Ho Jung) 한국가시화정보학회 2016 한국가시화정보학회지 Vol.14 No.1
We report a finding of fast(exceeding 2,000 K/s) heating of polydimethylsiloxane(PDMS), one of the most commonly-used microchannel materials, under cyclic loadings at high(~MHz) frequencies. A microheater was created based on the finding. The heating mechanism utilized vibration damping of sound waves, which were generated and precisely manipulated using a conventional surface acoustic wave(SAW) microfluidic system, in PDMS. The penetration depths were measured to range from 210 μm to 1290 μm, enough to cover most microchannel heights in microfluidic systems. The energy conversion efficiency was SAW frequency-dependent and measured to be the highest at around 30 MHz. Independent actuation of each interdigital transducer(IDT) enabled independent manipulation of SAWs, permitting spatiotemporal control of temperature on the microchip. All the advantages of this microheater facilitated a two-step continuous flow polymerase chain reaction(CFPCR) to achieve the billion-fold amplification of a 134 bp DNA amplicon in less than 3 min. In addition, a technique was developed for establishing dynamic free-form temperature gradients(TGs) in PDMS as well as in gases in contact with the PDMS.
김상복(Sang Bok Kim),윤상열(Sang Youl Yoon),성형진(Hyung Jin Sung),김상수(Sang Soo Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
A novel optical particle separating method is proposed and investigated theoretically and experimentally. On theoretical study, analytic expressions of radiation forces are derived using photon stream method and trajectories of particles in an optical particle separator are calculated. Furthermore, approximated retention distances of particles are derived analytically. On experimental study, optical particle separator is fabricated using conventional soft lithography method. Trajectories and retention distances of different-sized particles are observed and measured. The measured retention distances of different-sized particles are in good agreement with theoretical prediction.
박태선,성형진,Park, Tae-Seon,Sung, Hyung-Jin 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.5
Turbulent flow over a fully-developed wavy channel is investigated by the nonlinear $textsc{k}$-$\varepsilon$-f$_{u}$ model of Park et al.$^{(1)}$ The Reynolds number is fixed at Re$_{b}$ = 6760 through all wave amplitudes and the wave configuration is varied in the range of 0$\leq$a/λ$\leq$0.15 and 0.25$\leq$λ/H$\leq$4.0. The predicted results for wavy channel are validated by comparing with the DNS data of Maa$\beta$ and Schumann$^{(2)}$ The model performance Is shown to be generally satisfactory. As the wave amplitude increases, it is found that the form drag grows linearly and the friction drag is overwhelmed by the form drag. In order to verify these characteristics, a large eddy simulation is performed for four cases. The dynamic model of Germane et al.$^{(3)}$ is adopted. Finally, the effects of wavy amplitude on separated shear layer are scrutinized.