• Title, Summary, Keyword: bubble-point

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COMPUTATION OF TRANSITION FLOW WITH LAMINAR SEPARATION BUBBLE OVER AN AIRFOIL (익형의 층류박리를 동반한 천이 유동 해석)

  • Jeon, S.E.;Park, S.H.;Kim, S.H.;Byun, Y.H.;Lee, J.W.;Jung, K.J.
    • 한국전산유체공학회:학술대회논문집
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    • pp.60-64
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    • 2009
  • Laminar separation bubble and transitional flow over an airfoil are investigated at a moderate range of Reynolds numbers. In this research, a Reynolds-Averaged Navier-Stokes code is coupled with an empirical transition model that can predict transition onset points and the length of transition region. Without solving the boundary layer equations, approximated e-N method is directly applied to the RANS code and iteratively solved together. The computational results are compared with the experimental data for NACA0012 airfoil. Results of transition onset point and length are compared well with experimental and XFOIL prediction. In high angle of attack the present RANS results show better agreement than XFOIL results using the boundary layer equations.

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Numerical Simulation of the Aeroacoustic Noise in the Separated Laminar Boundary Layer

  • Park, Hyo-Won;Young J. Moon;Lee, Kyu-Jung
    • Journal of Mechanical Science and Technology
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    • v.17 no.2
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    • pp.280-287
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    • 2003
  • The unsteady flow characteristics and the related noise of separated incompressible laminar boundary layer flows (Re$\sub$$\delta$/* = 614, 868, and 1,063) are numerically investigated. The characteristic lines of the wall pressure are examined to identify the primary noise source, related with the unsteady motion of the vortex at the reattachment point of the separation bubble. The generation and propagation of the vortex-induced noise in the separated laminar boundary layer are computed by the method of Computational Aero-Acoustics (CAA), and the effects of Reynolds number, Mach number and adverse pressure gradient strength are examined.

A Study on WB(Water-Bubble) Based Highly Secure Flexible Network Section (WB(Water-Bubble) 기반의 강한 보안성을 갖는 탄력적 네트워크 구간에 관한 연구)

  • Seo, Woo-Seok
    • The Journal of the Korea institute of electronic communication sciences
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    • v.12 no.5
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    • pp.737-746
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    • 2017
  • In 2017, amid changes in the security market such as integrated security (IS) and convergence security (CS), a variety of security paradigms in terms of operation and management have been suggested. Rather than changing existing network infrastructure and bringing about fluid, multi-dimensional changes, these solutions and technologies focus entire security capacity on a primary protection, leading to network infrastructure suffering from unexpected inherent violations and problems in a continued manner. Therefore, it is time to propose and develop a flexible network section that can protect from attacks of similar pattern and concentrated traffic attacks by applying a new concept of WB (Water-Bubble) to network infrastructure and analyzing on the basis of experiment and installation. Methodology of the WB-based highly secure flexible network section proposed in this study is expected to provide materials for studies on how to achieve network section security taking into account three major limitations and security standards: fluidity, unpredictability, and non-area scalability by contact point ratio, by changing a network area predicted to be the final target of attack into resonant network section (area) with flexible area changes.

A Study on the Neutron in Radiation Treatment System and Related Facility (방사선치료 장치 및 관련시설에서의 산란 중성자에 관한 연구)

  • Kim Dae-Sup;Kim Jeong-Man;Lee Hee-Seok;Lim Ra-Seung;Kim You-Hyun
    • The Journal of Korean Society for Radiation Therapy
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    • v.17 no.2
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    • pp.141-145
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    • 2005
  • Purpose : It is known that the neutron is generally generated from the photon, its energy is larger than 10 MV. The neutron is leaked in the container inspection system installed at the customs though its energy is below 9 MV. It is needed that the spacial effect of the neutrons released from radiation treatment machine, linac, installed in the medical canter. Materials and Methods : The medical linear accelerator(Clinac 1800, varian, USA) was used in the experiment. Measuring neutron was used bubble detector(Bubble detector, BDPND type, BTI, Canada) which was created bubble by neutron. The bubble detector is located on the medical linear accelerator outskirt in three different distance, 30, 50, 120 cm and upper, lower four point from the iso-center. In addition, for effect on protect material we have measured eight points which are 50 cm distance from iso-center. The SAD(source-axis-distance), distance from photon source to iso-center, is adjusted to 100 cm and the field size is adjusted to $15{\times}15cm^2$. Irradiate 20 MU and calculate the dose rate in mrem/MU by measuring the number of bubble. Results : The neutron is more detected at 5 position in 30, 50 cm, 7 position in 120 cm and with wedge, and 2 position without mount. Conclusion : Though detection position is laid in the same distance in neutron measurement, the different value is shown in measuring results. Also, neutron dose is affected by the additional structure, the different value is obtained in each measurement positions. So, it is needed to measure and evaluate the neutron dose in the whole space considering the effect of the distance, angular distribution and additional structure.

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Dispersion in the Unsteady Separated Flow Past Complex Geometries (복합지형상에서 비정상 박리흐름에 의한 확산)

  • Ryu, Chan-Su
    • Journal of the Korean earth science society
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    • v.22 no.6
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    • pp.512-527
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    • 2001
  • Separated flows passed complex geometries are modeled by discrete vortex techniques. The flows are assumed to be rotational and inviscid, and a new techlnique is described to determine the stream functions for linear shear profiles. The geometries considered are the snow cornice and the backward-facing step, whose edges allow for the separation of the flow and reattachment downstream of the recirculation regions. A point vortex has been added to the flows in order to constrain the separation points to be located at the edges, while the conformal mappings have been modified in order to smooth the sharp edges and to let the separation points free to oscillate around the points of maximum curvature. Unsteadiness is imposed to the flow by perturbing the vortex location, either by displacing the vortex from the equilibrium, or by imposing a random perturbation with zero mean to the vortex in equilibrium. The trajectories of passive scalars continuously released upwind of the separation point and trapped by the recirculating bubble are numerically integrated, and concentration time series are calculated at fixed locations downwind of the reattachment points. This model proves to be capable of reproducing the trapping and intermittent release of scalars, in agreement with the simulation of the flow passed a snow cornice performed by a discrete multi-vortex model, as well as with direct numerical simulations of the flow passed a backward-facing step. The results of simulation indicate that for flows undergoing separation and reattachment the unsteadiness of the recirculating bubble is the main mechanism responsible for the intense large-scale concentration fluctuations downstream.

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Comparison of particle removal efficiency between the physical cleaning methods in the fabrication of liquid crystal displays (LCD 제조공정에서 물리적 세정법의 미립자 제거효율 비교 연구)

  • Park, Chang-Beom;Yi, Seung-Jun;Chang, In-Soung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.11 no.3
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    • pp.795-801
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    • 2010
  • As the fabrication technology of LCDs (Liquid Crystal Displays) advances, the size of mother glass substrates is getting larger, and the fabrication process is becoming finer. Accordingly, the importance of cleaning processes grows in the fabrication process of LCDs. In this study, we have compared and evaluated the particle removal efficiency for three different methods of physical cleaning, which are brush, bubble jet, and aqua/air cleaning. Using the seventh generation glass substrate, the particle removal efficiency has been investigated by changing operation conditions such as a flow rate of deionized water, pressure, contact depth between a brush bristle and a glass substrate, and so forth. In the case of brush cleaning, the cleaning efficiency barely changes after a critical point when the contact depth is varied. While the cleaning efficiency of bubble jet cleaning is almost independent of pressure, that of aqua/air cleaning is affected by pressure up to a critical point, but is not changed after it. We note the brush cleaning is the most effective among the three cleaning methods under our experimental conditions.

Transient behavior of cryogenic thermosiphon working with R14 and nitrogen mixture (R14와 질소 혼합유체를 사용하는 극저온 열사이펀의 과도상태 거동)

  • Lee, Ji-Sung;Jeong, Sang-Kwon
    • Progress in Superconductivity and Cryogenics
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    • v.12 no.1
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    • pp.66-70
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    • 2010
  • The operational temperature range of thermosiphon is generally limited from the critical point to the triple point of the working fluid to maintain two-phase state. Thermosiphon with mixed working fluid has a potential to widen the operational temperature range. In this study, the physical behavior of mixed working fluid during the transient operation of thermosiphon was analyzed with temperature-mole fraction diagram. The condenser and the evaporator temperature variations were explained by the dew line and the bubble line of the mixture. It is encouraging that the thermosiphon operation commences early with larger fraction of high boiling point component, but the temperature gap between the condenser and the evaporator due to the separation of two components has a negative effect on the officient cool down process.

Prediction of Intrinsic Pore Properties of Ultrafiltration Membrane by Solute Rejection Curves (용질배제 곡선에 의한 한외여과 막의 세공특성 예측)

  • 염경호
    • Proceedings of the Membrane Society of Korea Conference
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    • pp.4-8
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    • 1991
  • The characterization of pore properties (mean pore size and pore size distribution) of the active layer in a UF membrane is important not only in order to obtain information about the factors affecting pore formation during membrane manufacturing but also to understand deeply the mechanism of solute and solvent transport through pores. Many methods of characterizing quantitatively the pore properties of UF membranes have been suggested in the literature: solvent and gas flow measurement, bubble point determination, electron microscopy, gas adsorption/desorption measurement, rejection measurement etc. But most of these methods involve time-consuming procedures and involve some wellknown problems and uncertainties.

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Active control of flow over a sphere using electro-magnetic actuators (전자석 액츄에이터를 이용한 구 주위의 유동제어)

  • Park, Jin-Il;Choi, Hae-Cheon;Jeon, Woo-Pyung
    • Proceedings of the KSME Conference
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    • pp.497-501
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    • 2000
  • Flow over a sphere is controlled experimentally at $Re=10^5$ using electro-magnetic actuators. The electro-magnetic actuator developed in this study is composed of the permanent magnet electro-magnet membrane and slot. Eight actuators are placed inside the sphere at equally spaced intervals on a latitudinal plane and the position of the control slot is 76 from the stagnation point. Each actuator generates a periodic blowing and suction through the slot at variable frequencies of $10{\sim}140Hz$ and variable amplitudes by controlling electric signals applied to the electro-magnet. Drag on the sphere measured using a load cell is significantly reduced with control at the forcing frequencies larger than the natural shedding frequency $({\approx}14Hz\;at\;Re=10^5)$, whereas drag is slightly increased at the forcing frequency of 10Hz. It is shown from pressure measurement that the static pressure in the rear surface of the sphere is significantly increased with control, indicating that the separation is delayed due to control. Flow visualizations also show that the detaching shear layer is more attracted to the sphere center with control, the separation bubble size is significantly reduced, and motion inside the bubble is very weak, as compared to the case of uncontrolled flow.

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Subcultural Style in the Turn of the nst Century High Fashion -The Case of Punk Look- (21세기 전환기 하이패션에 나타난 하위문화 스타일 -펑크 룩을 중심으로-)

  • 임은혁
    • Journal of the Korean Society of Costume
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    • v.53 no.2
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    • pp.71-85
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    • 2003
  • In the turn of the century, fashion designers have not just drawn upon one or two subcultural styles but have extracted elements from many subcultures to use in a single collection. In true postmodern style these are freely combined with historical, cross-cultural and futuristic influences to create new fashions. The process could be explained by bubble-up phenomenon, retroism. pastiche and pursuit of pleasure. In the course of illustrating subcultural styles transformed into mainstream fashion, the case of Punk was studied as a turning point of modernist and postmodern period which have been introduced by high fashion designers since the birth in 1976. The following cases have continued to appear entering upon the third millennium and the aesthetic value of those can be summarized as ambiguity, eclecticism, and deconstruction. In other words. the energy and authenticity of Punk has been considered to be desirable in high fashion, however designers focus on clothing and adornment rather than ideology and lifestyle. The aesthetic property of subcultural style defeats the established notion of standardized fashion and stimulates new consciousness. which allows a room to be diversified and subdivided.