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격자 볼츠만 방법을 이용한 미세 섬유 다공성 매질의 투과율에 관한 수치적 연구
조현준(H. Cho),정남균(N. Jeong),성형진(H.J. Sung) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11
We calculated the permeability of micro-scale fibrous porous media using the lattice Boltzmann method. We constructed two models of overlapping fibers, and another two models of non-overlapping fibers. The effect of fiber overlapping on the permeability is investigated. The overlapping fibers yield up to 2 times larger value of permeability than the non-overlapping fibers. As the diameter of fiber increases, the fibers act as the granular inclusions. However, we obtained a correlation between the permeability and the porosity, which is useful in a wide range of the porosity, and is applicable to all fiber arrangements.
안준선(J. Ahn),이재화(J.H. Lee),성형진(H.J. Sung) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
Direct numerical simulations of turbulent boundary layers over three-dimensional cubic roughness arrays were performed to investigate the effects of the spanwise spacing on turbulent characteristics. The staggered cube arrays were arranged periodically on the streamwise direction with varying p<SUB>s</SUB>/k at fixed p<SUB>x</SUB>/k. The wall-friction parameters have the maximum contribution at p<SUB>x</SUB>/k=3. The outer peak of the Reynolds stresses are increased with increasing p<SUB>x</SUB>/k which indicates the wall similarity is not satisfied with all cases. The size of the low-momentum regions over the rough walls is larger than the smooth wall, and the vortical structures grow to the outer layer. The vortical structures start to develop at the edges of the cubes. As p<SUB>x</SUB>/k increases the roughness array becomes sparse and the vortical structures grow to the outer region because other near vortical structures do not disturb to each other.
압축공기시스템 에너지 절약을 위한 servo valve의 유동해석
박홍범(H. B. Park),성형진(H. J. Sung),류동렬(D. R. Ryu),김영석(Y. S. Kim) 유공압건설기계학회 2008 유공압건설기계학회 학술대회논문집 Vol.2008 No.10
In this paper, analysis of pressure and flow characteristics have been performed with a servo valve. A number of servo valve have been used in various applications including the inserting device, bearing transportation and welding machine. By analysis of flow and pressure gradient, technology can be obtained about optimal simulation of high response servo for competitiveness. Spool displacement and ratio of inlet/outlet pressure can give big effects to flow and pressure inside servo valve.
이진(J. Lee),장성재(S.J. Jang),성형진(H.J. Sung) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
Direct numerical simulations were carried out to investigate the turbulence statistics and coherent structures in a fluid flow through a conical diffuser for three opening angles of 2°, 4°, and 8°. To simulate the flow in the conical diffuser, we introduced the generalized coordinates for the streamwise and radial directions and used a cylindrical coordinate along the azimuthal direction. The adverse pressure gradient affected, the axisymmetric flow such that the streamwise component of the turbulence intensity was sensitive to the diffuser in the outer region. The maximum Reynolds shear stress increased as the opening angle increased. The premultiplied energy spectra showed that the most energetic wall-normal height and its wave length increased when the opening angle increased. Time-resolved instantaneous flow fields and two-point correlation functions provided evidence for the streamwise merging of low-speed streaking structures. The outer vortical structures shifted toward the diffuser axis as the flow passed the diffuser throat. The swirling motions of the individual hairpins in the outer region were stronger in the diffuser flow than in the straight pipe flow.