• Title/Summary/Keyword: Point Vortex

Search Result 189, Processing Time 0.027 seconds

A study on the change of turbulence structure in a diffuser (확대관의 난류구조 변동에 관한 연구)

  • Lee, Jang-Hwan;Han,Yong-Un
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.21 no.4
    • /
    • pp.503-508
    • /
    • 1997
  • The change of the structure of homogeneous turbulence subject to irrotational strains has been studied in an anti-Morel type diffuser (center matched cubic contour) using the hot wire anemometry. It was observed that the profiles of mean velocities and turbulence velocities along the center line were stable at the entrance region but rapidly changed near the matching point. The wall induced turbulence at the entrance region grows fast and was diffused toward the center at downstream. It was also observed that the axial turbulence grows faster than the radial one in the middle region of the diffusing flow and that the diffusing process has the vortex compression mechanism due to the conservation of angular momentum. These phenomena are frequently observed at the initial flow region of the free jet.

A Study on Flow Characteristics of Confined Circular Jet within Pipe (이중원관 구속제트의 유동특성에 관한 연구)

  • Seo M. S.;Choi J. W.;Lee Y. H.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 1997.10a
    • /
    • pp.136-142
    • /
    • 1997
  • The present study is aimed to investigate flow characteristics of confined jet flow within circular pipe. Numerical method based upon revised SOLA scheme which secures conservation form of convective terms on irregular grids by interpolating the variables appearing in staggered meshes is adopted on cylindrical coordinate formation. Computation was carried out for two kinds of Reynolds number, $10^5\;and\;1.5{\times}10^5$ defined by diameter of outer pipe and time-mean driving jet velocity. Results show that periodic vortex shedding from the jet mixing layer is profound and related unsteady flow characteristics prevail over the entire region. Spatial distribution of pressure and kinetic energy, fluctuation of static wall pressure, together with radial velocity components are examined in terms of instantaneous and time-mean point of views.

  • PDF

Unsteady Fluid Forces Acting on a Pitching Foil (피칭 운동익에 작용하는 비정상 유체력)

  • Yang, C.J.
    • The KSFM Journal of Fluid Machinery
    • /
    • v.8 no.6 s.33
    • /
    • pp.47-54
    • /
    • 2005
  • An oscillating foil can produce a driving force through the generation of a reversed $K\'{a}rm\'{a}n$ vortex street, and it can be expected to be a new highly effective propulsion system. A simple pitching foil model was made and it was operated within a water channel. The wake formation behind a pitching foil was visualized and unsteady fluid forces were measured using a 6-axis force sensor based on force and moment detectors. We have been examined various conditions such as reduced frequency, amplitude and pivot point in NACA 0010. The results showed that thrust coefficients increased with a reduced frequency. We also presented the experimental results on the characteristics of a pitching foil at various parameters.

Mixing Characteristics of Kerosene-Lox in a Swirl Injector at 100 bar

  • Heo, Junyoung;Kang, Jeongseok;Sung, Hong-Gye
    • International Journal of Aerospace System Engineering
    • /
    • v.3 no.1
    • /
    • pp.30-38
    • /
    • 2016
  • The The turbulent mixing characteristics of Kerosene-LOx in a coaxial swirl injector 100 bar have been numerically investigated. Turbulent model is based on large eddy simulation with real-fluid transport and thermodynamics. The effects of equation of state (EOS), chamber pressure are evaluated in a point of the mixing efficiency and pressure fluctuations. The dominant frequency is same as the hairpin vortex shedding frequency generated by film wave at the LOx post.

Wakes of two inline cylinders at a low Reynolds number

  • Zafar, Farhan;Alam, Md. Mahbub;Muhammad, Zaka;Islam, Md.
    • Wind and Structures
    • /
    • v.29 no.1
    • /
    • pp.55-64
    • /
    • 2019
  • The effect of vortex impingement on the fluid dynamics around a cylinder submerged in the wake of another of different diameters is numerically investigated at a Reynolds number Re = 200. While the diameter (D) of the downstream cylinder is fixed, impinging vortices are produced from the upstream cylinder diameter (d) varied as d/D = 0.24, 0.4, 0.6, 0.8 and 1.0, with a spacing ratio L=5.5d, where L is the distance between the center of the upstream cylinder to the front stagnation point of the downstream cylinder. Two-dimensional simulations are carried out using the finite volume method. Fluid forces acting on the two cylinders are correlated with impinging vortices, vortex shedding, and wake structure. Different facets of wake formation, wake structure, and flow separation and their connections to fluid forces are discussed.

Optimization of slope angles of a barge-shaped FPSO from the towing stability and load perspective

  • Kwon, Chang Seop;Yeon, Seong Mo
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.13 no.1
    • /
    • pp.786-793
    • /
    • 2021
  • In this study, a parametric investigation is performed using CFD for towing stability and loads according to the forward and aft slope angles of a barge-shaped FPSO. The forward slope angle is considered in a range of 30-60° and the aft slope is examined in a range of 20-50°. As a result of a comparative study based on CFD towing simulations, it is found that the yaw motion is damped out and stabilized when the aft slope is more than 40° regardless of the forward slope angle. The vortex contours in the y-axis plane near the aft slope are analyzed and it is observed that the vortex developed at the bottom knuckle is bent upward along the aft slope when the aft slope is less than 40°, and completely fallen from the bottom knuckle when the aft slope is more than 40°. Based on the results, a guide to forward and aft slope angles of a barge-shaped FPSO is presented from a practical point of view considering towing stability as well as towing load.

Optimal Operating Condition of Vortex Separator for Combined Sewer Overflows Treatment (합류식 하수관거 월류수 처리를 위한 와류형 분리장치의 최적 운전조건)

  • Han, Jung-kyun;Joo, Jae-young;Lee, Bum-joon;Na, Ji-hun;Park, Chul-hwi
    • Journal of Korean Society of Water and Wastewater
    • /
    • v.23 no.5
    • /
    • pp.557-564
    • /
    • 2009
  • A combined sewer system can quickly drain both storm water and sewage, improve the living environment and resolve flood measures. A combined sewer system is much superior to separate sewer system in reduction of the non-point source pollutant load. However, during rainfall. it is impossible in time, space and economic terms to cope with the entire volume of storm water. A sewage system that exceeds the capacity of the sewer facilities drain into the river mixed with storm-water. In addition, high concentration of CSOs by first-flush increase pollution load and reduce treatment efficiency in sewage treatment plant. The aim of this study was to develope a processing unit for the removal of high CSOs concentrations in relation to water quality during rainfall events in a combined sewer. The most suitable operational design for processing facilities under various conditions was also determined. With a designed discharge of 19.89 m/min, the removal efficiency was good, without excessive overflow, but it was less effective in relation to underflow, and decreased with decreasing particle size and specific gravity. It was necessary to lessen radius of vortex separator for increasing inlet velocity in optimum range for efficient performance, and removal efficiency was considered to high because of rotation increases through enlargement of comparing height of vortex separator in diameter. By distribution of influent particle size, the actual turbulent flow and experimental results was a little different from the theoretical removal efficiency due to turbulent effect in device.

Investigation of crossflow features of a slender delta wing

  • Tasci, Mehmet O.;Karasu, Ilyas;Sahin, Besir;Akilli, Huseyin
    • Wind and Structures
    • /
    • v.31 no.3
    • /
    • pp.229-240
    • /
    • 2020
  • In the present work, the main features of primary vortices and the vorticity concentrations downstream of vortex bursting in crossflow plane of a delta wing with a sweep angle of Λ=70° were investigated under the variation of the sideslip angles, β. For the pre-review of flow structures, dye visualization was conducted. In connection with a qualitative observation, a quantitative flow analysis was performed by employing Particle Image Velocimetry (PIV). The sideslip angles, β were varied with four different angles, such as 0°, 4°, 12°, and 20° while angles of attack, α were altered between 25° and 35°. This study mainly focused on the instantaneous flow features sequentially located at different crossflow planes such as x/C=0.6, 0.8 and 1.0. As a summary, time-averaged and instantaneous non-uniformity of turbulent flow structures are altered considerably resulting in non-homogeneous delta wing surface loading as a function of the sideslip angle. The vortex bursting location on the windward side of the delta wing advances towards the leading-edge point of the delta wing. The trajectory of the primary vortex on the leeward side slides towards sideways along the span of the delta wing. Besides, the uniformity of the lift coefficient, CL over the delta wing plane was severely affected due to unbalanced distribution of buffet loading over the same plane caused by the variation of the sideslip angle, β. Consequently, dissimilarities of the leading-edge vortices result in deterioration of the mean value of the lift coefficient, CL.

PIV Aanalysis of Vortical Flow behind a Rotating Propeller in a Cavitation Tunnel (캐비테이션 터널에서 PIV를 이용한 프로펠러 후류 보오텍스 유동계측 및 거동해석)

  • Paik, Bu-Geun;Kim, Jin;Park, Young-Ha;Kim, Ki-Sup;Kim, Kyoung-Youl
    • Journal of the Society of Naval Architects of Korea
    • /
    • v.42 no.6 s.144
    • /
    • pp.619-630
    • /
    • 2005
  • A two-frame PIV (Particle Image Velocimetry) technique is used to investigate the wake characteristics behind a marine propeller with 4 blades at high Reynolds number. For each of 9 different blade phases from $ 0^{\circ} $ to $ 80^{\circ} $, one hundred and fifty instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors En the propeller wake legion. The slipstream contraction occurs in the near-wake region up to about X/D : 0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point.

A Study on Flow Control of Open Cavity with Inclined Rear Walls (경사벽면을 갖는 개방 캐비티의 유동제어에 관한 연구)

  • Cho, Dae-Hwan;Jin, Wan-Bin
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.33 no.8
    • /
    • pp.1180-1186
    • /
    • 2009
  • This experimental study is about the flow characteristics according to existence and nonexistence of the control rod and location in the flow field where it has the Inclined rear walls in the open cavity. By using the visualization of flow and particle image velocimetry (PIV), we performed about a change and speed of the Reynolds number. Our objective was what part of the control rod gives less effects to the characteristics of flow and how the shear mixing layer moves at what critical point of the Reynolds number. As a result, we differed the location of control rod. So finally, L/H=0.2 was discovered to give less effects to the cavity. The flow of backside of vortex faces the upper side. And we found that this phenomenon shows up more clear when the number of Reynolds increases. This is because of the flow of vortex causes by the condition of y/H=1.0. This phenomenon gets more clear with increasing of number of Reynolds, and critical point of the Reynolds number was $Re=1.0{\times}10^4$ around. If control rod is L/H=0.1, depending on the number of Reynolds ($Re=6.0{\times}10^3$, $Re=8.0{\times}10^3$, $Re=1.0{\times}10^4$, $Re=1.2{\times}10^4$), doubled vortex shows up. As the shear mixing layer of the upper side of cavity increases, the speed of the lower side was very stable.