• Title/Summary/Keyword: contrast flow

Search Result 499, Processing Time 0.025 seconds

Behavior of Tip Vortex in a Propeller Fan (프로펠러팬에서의 Tip Vortex 거동)

  • Kim, Sung-Hyup;Furukawa, Masato;Inoue, Masahiro
    • Proceedings of the KSME Conference
    • /
    • 2004.11a
    • /
    • pp.1377-1382
    • /
    • 2004
  • Flow fields in a half ducted propeller fan have been investigated by three-dimensional Reynolds-averaged Navier-Stokes (RANS) simulations and a vortex core identification technique. The simulation at the design operating condition shows that the tip vortex onset point is located at 30 percent tip chord of the suction surface on the blade tip. There is no interaction between the tip vortex and the adjacent blade, so that the tip vortex smoothly convects to the rotor exit. However, the high vorticity in the tip vortex causes the wake and the tip leakage flow to be twined around the tip vortex and to interact with the pressure surface of the adjacent blade. This flow behavior corresponds well with experimental results by Laser Doppler Velocimetry. On the contrary, the simulation at the low-flowrate operating condition shows that the tip vortex onset point is located at the 60 percent tip chord of the suction surface. In contrast to the design operating condition, the tip vortex grows almost tangential direction, and impinges directly on the pressure surface of the adjacent blade.

  • PDF

Clinical Implication of Mechanical Insufflation-Exsufflation Method in Patients with Duchenne muscular dystrophy (뒤시엔느 근이영양증 환자에게 기계적 기침보조기법 적용의 임상적 의의)

  • Kim, Myung-Kwon;Ji, Sang-Gu
    • Journal of the Korean Society of Physical Medicine
    • /
    • v.6 no.4
    • /
    • pp.407-414
    • /
    • 2011
  • Purpose : The aim of this study was to clarify the lung capacity, maximal insufflation capacity, and peak cough flow when a mechanical insufflation-exsufflation(MIE) method was used to increase Duchenne muscular dystrophy patients' lung function. Methods : The subjects of the study were 21 patients with Duchenne muscular dystrophy. They were randomly selected from patients within the boundaries of the selection criteria, and divided into two groups; The subject group(n=11) used the mechanical insufflation-exsufflation method with traditional therapeutic exercise. The control group(n=10) used only traditional therapeutic exercise. Results :The results indicated that maximal insufflation capacity, unassisted peak cough flow and assisted peak cough flow significantly increased in the subject group(p<.05). By contrast, in the control group, the results didn't indicate the significant differences from the variable. There were significant differences in maximal insufflation capacity and assisted peak cough flow between the subject group and the control group before and after the application of the mechanical insufflation-exsufflation method. Conclusion : A mechanical insufflation-exsufflation method has positive effects on the improvements of cough functions and that of pulmonary functions such as lung volume, lung elasticity in patients with Duchenne muscular dystrophy.

Buoyancy Effect on Stable and Oscillating Lifted Flames in Coflow Jets for Highly Diluted Propane (질소희석된 프로판 동축류 버너에서 부상화염에 대한 부력효과)

  • Kim, Jun-Hong;Shin, Moo-Kyung;Chung, Suk-Ho
    • 한국연소학회:학술대회논문집
    • /
    • 2001.06a
    • /
    • pp.9-16
    • /
    • 2001
  • When large size nozzle with low jet velocity is used, the buoyancy effect arises from the density difference among propane, air, and burnt gas. Flame characteristics in such buoyant jets have been investigated numerically to elucidate the effect of buoyancy on lifted flames. It has been demonstrated that the cold jet has circular cone shape since upwardly injected propane jet decelerates and forms stagnation region. In contrast to the cold flow, the reacting flow with a lifted flame has no stagnation region by the buoyancy force induced from the burnt gas. To further illustrate the buoyancy effect on lifted flames, the reacting flow with buoyancy is compared with non-buoyant reacting flow. Non-buoyant flame is stabilized at much lower height than the buoyant flame. At a certain range of fuel jet velocities and fuel dilutions. an oscillating flame is demonstrated numerically showing that the height of flame base and tip vary during one cycle of oscillation. Under the same condition. non-buoyant flame exhibits only steady lifted flames. This confirms the buoyancy effect on the mechanism of lifted flame oscillation.

  • PDF

Compressibility correction of the Panel Method in Flow Analysis of a High Subsonic Turbine Cascade (고 아음속 터빈 캐스케이드 유동 해석을 위한 패널법의 압축성 보정)

  • Kim, Hark-Bong;Kim, Jin-Kon;Kwak, Jae-Su;Kang, Jeong-Seek
    • Proceedings of the Korean Society of Propulsion Engineers Conference
    • /
    • 2007.11a
    • /
    • pp.49-54
    • /
    • 2007
  • Flow analysis in a turbine cascade by Euler or Navier-Stokes equation gives relatively accurate solution, however, those method require large computer memory or computing time. on contrast, the panel method, which is applied to incompressible and inviscid flow, provides fast and reasonal solution but the compressibility correction is required for a high air velocity case. In this paper, the compressibility corrected panel method was applied in order to find velocity distribution on turbine blades. Results showed that the calculated velocity in a turbine cascade by the compressibility corrected panel method gave good agreement with experimental results or the solution by finite volume method for compressible flow.

  • PDF

Performance of an Active Stimulating Device Using a Rope Kite or Array in the Cod End to Reduce Juvenile by-catch

  • Kim, Yong-Hae
    • Fisheries and Aquatic Sciences
    • /
    • v.13 no.2
    • /
    • pp.182-189
    • /
    • 2010
  • An active stimulating device (ASD) using a rope apparatus may operated by the flow of turbulence inside a cod end, generating variable stimuli in addition to flow-related effects to minimize the by-catch of juvenile fishes. Preliminary testing involved a hydrodynamic effect inside the cod end with a rotating rope kite or conical rope array to generate variable stimuli (visual stimuli, water flow, or physical contact with fish) to change fish position. The experimental rope kite offered more choice in rotating period and range of sweeping action; adjusting the towing line or flow velocity helped to drive fish toward the net panel and encouraged escape. The conical shape of the rope array in the cod end helped to clear a path for fish by disturbing the rigging and providing more contrast between objects, preventing an optomotor response. This enabled more black porgy to be herded toward the net at an early stage of towing. Therefore, either a conical rope array or a rotating rope kite can be used as an effective ASD to prevent juvenile by-catch.

Compressibility correction of the Panel Method in Flow Analysis of a High Subsonic Turbine Cascade (고 아음속 터빈 캐스케이드 유동 해석을 위한 패널법의 압출성 보정)

  • Kim, Hark-Bong;Kim, Jin-Kon;Kwak, Jae-Su;Kang, Jeong-Seek
    • Journal of the Korean Society of Propulsion Engineers
    • /
    • v.12 no.1
    • /
    • pp.23-28
    • /
    • 2008
  • Flow analysis in a turbine cascade by Euler or Navier-Stokes equation gives relatively accurate solution, however, those method require large computer memory or computing time. On contrast, the panel method, which is applied to incompressible and inviscid flow, provides fast and reasonal solution but the compressibility correction is required for a high air velocity case. In this paper, the compressibility corrected panel method was applied in order to find velocity distribution on turbine blades. Results showed that the calculated velocity in a turbine cascade by the compressibility corrected panel method gave good agreement with the solution by finite volume method for compressible flow.

Process Performance and Bacterial Community Structure Under Increasing Influent Disturbances in a Membrane-Aerated Biofilm Reactor

  • Tian, Hailong;Yan, Yingchun;Chen, Yuewen;Wu, Xiaolei;Li, Baoan
    • Journal of Microbiology and Biotechnology
    • /
    • v.26 no.2
    • /
    • pp.373-384
    • /
    • 2016
  • The membrane-aerated biofilm reactor (MABR) is a promising municipal wastewater treatment process. In this study, two cross-flow MABRs were constructed to explore the carbon and nitrogen removal performance and bacterial succession, along with changes of influent loading shock comprising flow velocity, COD, and NH4-N concentrations. Redundancy analysis revealed that the function of high flow velocity was mainly embodied in facilitating contaminants diffusion and biosorption rather than the success of overall bacterial populations (p > 0.05). In contrast, the influent NH4-N concentration contributed most to the variance of reactor efficiency and community structure (p < 0.05). Pyrosequencing results showed that Anaerolineae, and Beta- and Alphaproteobacteria were the dominant groups in biofilms for COD and NH4-N removal. Among the identified genera, Nitrosomonas and Nitrospira were the main nitrifiers, and Hyphomicrobium, Hydrogenophaga, and Rhodobacter were the key denitrifiers. Meanwhile, principal component analysis indicated that bacterial shift in MABR was probably the combination of stochastic and deterministic processes.

The Effect of Left Subclavian Artery Coverage During Endovascular Repair of the Thoracic Aortic Aneurysm on Cerebral Hemodynamics: Two Cases of Flow Measurement by using 2D Phase Contrast Magnetic Resonance Imaging (흉부대동맥류의 혈관내치료 도중 좌측 쇄골하동맥 폐색이 뇌혈류역동에 미치는 효과: 2차원 위상차 대조 자기공명영상을 이용한 혈류 측정 2례 보고)

  • Baek, Seung-Hoon;Youn, Sung-Won;Kim, Ho-Kyun;Kwon, Oh-Choon;Lee, Sub;Lee, Jong-Min
    • Investigative Magnetic Resonance Imaging
    • /
    • v.16 no.2
    • /
    • pp.159-168
    • /
    • 2012
  • The proximity of thoracic aortic aneurysm to the left subclavian artery (LSA) has made the coverage of LSA during thoracic endovascular aortic repair (TEVAR) be essential. Despite controversy concerning the safety of LSA coverage and the indications for LSA revascularizations, the cerebral hemodynamic change after LSA coverage has not been demonstrated. We prospectively examined two patients who would undergo TEVAR with LSA coverage by using 2D cine phase contrast MR imaging. After LSA coverage, the left subclavian steal was properly compensated by the increased flow volumes of both carotid arteries and right vertebral artery, which is the major collateral supply. The total brain supply after TEVAR did not lessen, which showed good correlation with uneventful clinical outcome. Therefore, 2D phase contrast MR imaging can be recommended as a useful technique to evaluate the hemodynamic change of the LSA coverage during TEVAR and to triage the candidate for LSA revascularization.

Optimization of Protocol for Injection of Iodinated Contrast Medium in Pediatric Thoracic CT Examination (소아 흉부 CT검사에서 조영제 주입에 관한 프로토콜의 최적화)

  • Kim, Yung-Kyoon;Kim, Yon-Min
    • Journal of the Korean Society of Radiology
    • /
    • v.13 no.6
    • /
    • pp.879-887
    • /
    • 2019
  • The purpose of this study is to establish a physiological injection protocol according to body weight, in order to minimize amount of contrast medium and optimize contrast enhancement in pediatric patients performing thoracic CT examinations. The 80 pediatric patients under the age of 10 were studied. Intravenous contrast material containing 300 mgI/ml was used. The group A injected with a capacity of 1.5 times its weight, and groups B, C and D added 5 to 15 ml of normal saline with a 10% decrease in each. The physiologic model which can be calculated by weight about amount of injection of contrast medium and normal saline, flow rate and delay time were applied. To assess image quality, measured average HU value and SNR of superior vena cava, pulmonary artery, ascending and descending aorta, right and left atrium, right and left ventricle. CT numbers of subclavian vein and superior vena cava were compared to identify the effects of reducing artifacts due to normal saline. Comparing SNR according to the contrast medium injection protocol, significant differences were found in superior vena cava and pulmonary artery, descending aorta, right and left ventricle, and CT numbers showed significant differences in all organs. In particular, B group with a 10% decrease in contrast medium and an additional injection of saline showed a low degree of contrast enhancement in groups with a decrease of more than 20%. In addition, the group injected with normal saline greatly reduced contrast enhancement of subclavian vein and superior vena cava, and the beam hardening artifact by contrast medium was significantly attenuated. In conclusion, the application of physiological protocol for injection of contrast medium in pediatric thoracic CT examinations was able to reduce artifacts by contrast medium, prevent unnecessary use of contrast medium and improve the effect of contrast enhancement.

Wind Effects on Tidal Currents in Gamak Bay

  • Lee, Moon-Ock;Kim, Byeong-Kuk
    • Journal of Ocean Engineering and Technology
    • /
    • v.23 no.2
    • /
    • pp.18-27
    • /
    • 2009
  • This study was conducted to examine the effect of wind on the circulation of seawater in Gamak Bay, which contains numerous farms for fish and shellfish but suffers a significant loss by fisheries nearly annually from harmful algal blooms. In numerical experiments with a simplified bathymetry for Gamak Bay, the wind in summer appeared to more strongly influence the east-westward flow than the south-northward flow. In winter, this trend was nearly similar to the summer but seemed to have a greater effect on the flow at the north-west of the bay than the flow at the south mouth of the bay. On the other hand, in numerical experiments with a realistic bathymetry for Gamak Bay, the wind in summer appeared to more strongly influence the east-westward flow than the south-northward flow. Furthermore, the effect of the wind was stronger at the south mouth of the bay than at the north-west of the bay. In contrast, the wind in winter affected the east-westward flow more strongly and its effect appeared stronger at the north-west of the bay than at the south mouth of the bay. In addition, the effect of the wind tended to increase with distance from the east to the west. Therefore, the tidal currents in Gamak Bay proved to be strongly influenced by the wind, in particular east-westward. However, some measures are urgently required to improve the water quality of the bay, since the south-northward flow turned out to be obstructed by an east-westward shoal located in the middle of the bay.