• Title/Summary/Keyword: flow contraction

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Development of Calibration Jet System for Calibrating a Flow Sensor (유동센서 보정용 캘리브레이션 제트 시스템 개발)

  • Chang, J.W.;Byun, Y.H.
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.11 no.1
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    • pp.41-55
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    • 2003
  • A calibration jet system using separate blower is developed to calibrate a flow sensor effectively. Designed open circuit type mini calibration jet system, which has the dimension of $0.5m(W){\times}1.17m(H)$ is small compared with conventional calibration jet systems. The exit of nozzle has exchangeable contractions with a cross section area of $38.5cm^2$ , and a cross section area of $113.1cm^2$, respectively. The ranges of wind speed at exit of exchangeable nozzles are $7.5{\sim}42\;m/s$ and $1.8{\sim}16.5\;m/s$, respectively. The input power for the high pressure blower is 1.18kW. The turning vanes for corner was rolled flat plate parallel to the flow direction. The flow conditioning screen was located immediately downstream of the wide-angle diffuser. The honeycomb and two flow conditioning screens were located in the stagnation chamber. From the economical point of view and the simplicity of the calibration jet system set up and handling, it can be said that the developed calibration jet system is an effective calibration jet system. This system can also be used to calibrate the flow sensor with high resolution.

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An Omnidirectional Vision-Based Moving Obstacle Detection in Mobile Robot

  • Kim, Jong-Cheol;Suga, Yasuo
    • International Journal of Control, Automation, and Systems
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    • v.5 no.6
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    • pp.663-673
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    • 2007
  • This paper presents a new moving obstacle detection method using an optical flow in mobile robot with an omnidirectional camera. Because an omnidirectional camera consists of a nonlinear mirror and CCD camera, the optical flow pattern in omnidirectional image is different from the pattern in perspective camera. The geometry characteristic of an omnidirectional camera has influence on the optical flow in omnidirectional image. When a mobile robot with an omnidirectional camera moves, the optical flow is not only theoretically calculated in omnidirectional image, but also investigated in omnidirectional and panoramic images. In this paper, the panoramic image is generalized from an omnidirectional image using the geometry of an omnidirectional camera. In particular, Focus of expansion (FOE) and focus of contraction (FOC) vectors are defined from the estimated optical flow in omnidirectional and panoramic images. FOE and FOC vectors are used as reference vectors for the relative evaluation of optical flow. The moving obstacle is turned out through the relative evaluation of optical flows. The proposed algorithm is tested in four motions of a mobile robot including straight forward, left turn, right turn and rotation. The effectiveness of the proposed method is shown by the experimental results.

Numerical study on the characteristics of the flow through injector orifice by multi-block computations (다중블럭계산에 의한 분사기 오리피스 유동특성 해석)

  • Kim, Yeong-Mok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.3
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    • pp.414-426
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    • 1997
  • Numerical computations were conducted to characterize the three-dimensional laminar flow through an injector orifice having an inclined angle of 30 .deg.. For this study, the incompressible Navier-Stokes equations in generalized curvilinear coordinates, using a pseudocompressibility approach for continuity equation, were solved. The computations were performed using the finite difference implicit, approximately factored scheme of Beam and Warming and multi-block grids of complete continuity at block interfaces. The multi-block computations were validated for the steady state using direct comparison of multi-block solutions with equivalent single-block ones, including 2-D 180.deg. TAD and 3-D 90.deg. pipe bend. The comparisons between the numerical solutions and the flow field measurements for a tube with sudden contraction were presented in this work for solution validation. Computational results showed the nature of complex flow fields within the inclined injector orifice, including strong pressure-driven secondary flows in the cross stream induced by the effect of streamline curvature. In addition, asymmetric secondary flows were induced in the Reynolds number range above assumed laminar flow regime considered. However, turbulence calculations and grid dependency studies are needed for more accurate computations.

Characteristics of Internal Flow and Fuel Spray in a Fuel Nozzle Orifice (연료노즐의 내부유동 및 외부분무 특성)

  • Hong, S.T.;Park, J.H.;Koo, J.Y.
    • Journal of ILASS-Korea
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    • v.1 no.1
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    • pp.76-84
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    • 1996
  • The nozzle geometry and up-stream inject ion condition affect the characteristics of flow inside the nozzle. such as turbulence and cavitation bubbles. Flow details in fuel nozzle orifice with sudden contraction of cross sectional area have been investigated both experimentally and numerically. The measurements of velocities of internal flow in a scaled-up nozzle with different length to diameter rat io(L/d) were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds numbers. The turbulent intensity and turbulence kinetic energy in a sharp inlet nozzle were higher than that in a round inlet nozzle. Calculations were also performed for the same nozzles as scaled-up experimental nozzles using the SIMPLE algorithm. External spray behavior under different nozzle geometry and up-stream flow conditions using Doppler technique and visualization technique were also observed.

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Numerical Analysis on Flow Characteristics of a Vane Pump (Vane Pump의 유동 특성에 대한 수치 해석)

  • Lee, Sang-Hyuk;Jin, Bong-Yong;Hur, Nahm-Keon
    • The KSFM Journal of Fluid Machinery
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    • v.10 no.1 s.40
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    • pp.34-40
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    • 2007
  • In this study, the characteristic of a vane pump of automotive power steering system is numerically analyzed. The vane pump changes the energy level of operation fluid by converting mechanical input power to hydraulic output. To simulate this mechanism, moving mesh technique is adopted. As a result, the flow rate and pressure are obtained by numerical analysis. The flow rate agrees well with the experimental data. Moreover, the variation and oscillation of the pressure around the rotating vane are observed. As a result of flow characteristics, The difference of pressure between both side of vane tip causes the back flow into the rotor. As the rotational velocity increases, the flow rate at the outlet and the pressure in the vane tip rises with higher amplitude of oscillation. In order to reducing the oscillation, the design of devices for decreasing the cross-area of the outlet part and returning the flow from the outlet to the inlet is required.

Optical Flow for Motion Images with Large Displacement by Functional Expansion

  • Kim, Jin-Woo
    • Journal of Korea Multimedia Society
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    • v.7 no.12
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    • pp.1680-1691
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    • 2004
  • One of the representative methods of optical flow is a gradient method which estimates the movement of an object based on the differential of image brightness. However, the method is ineffective for large displacement of the object and many improved methods have been proposed to copy with such limitations. One of these improved techniques is the multigrid processing, which is used in many optical flow algorithms. As an alternative novel technique we have been proposing an orthogonal functional expansion method, where whole displacements are expanded from low frequency terms. This method is expected to be applicable to flow estimation with large displacement and deformation including expansion and contraction, which are difficult to cope with by conventional optical flow methods. In the orthogonal functional expansion method, the apparent displacement field is calculated iteratively by a projection method which utilizes derivatives of the invariant constraint equations of brightness constancy. One feature of this method is that differentiation of the input image is not necessary, thereby reducing sensitivity to noise. In this paper, we apply our method to several real images in which the objects undergo large displacement and/or deformation including expansion. We demonstrate the effectiveness of the orthogonal functional expansion method by comparing with conventional methods including our optimally scaled multigrid optical flow algorithm.

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Finite element modeling of high Deborah number planar contraction flows with rational function interpolation of the Leonov model

  • Youngdon Kwon;Kim, See-Jo;Kim, Seki
    • Korea-Australia Rheology Journal
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    • v.15 no.3
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    • pp.131-150
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    • 2003
  • A new numerical algorithm of finite element methods is presented to solve high Deborah number flow problems with geometric singularities. The steady inertialess planar 4 : 1 contraction flow is chosen for its test. As a viscoelastic constitutive equation, we have applied the globally stable (dissipative and Hadamard stable) Leonov model that can also properly accommodate important nonlinear viscoelastic phenomena. The streamline upwinding method with discrete elastic-viscous stress splitting is incorporated. New interpolation functions classified as rational interpolation, an alternative formalism to enhance numerical convergence at high Deborah number, are implemented not for the whole set of finite elements but for a few elements attached to the entrance comer, where stress singularity seems to exist. The rational interpolation scheme contains one arbitrary parameter b that controls the singular behavior of the rational functions, and its value is specified to yield the best stabilization effect. The new interpolation method raises the limit of Deborah number by 2∼5 times. Therefore on average, we can obtain convergent solution up to the Deborah number of 200 for which the comer vortex size reaches 1.6 times of the half width of the upstream reservoir. Examining spatial violation of the positive definiteness of the elastic strain tensor, we conjecture that the stabilization effect results from the peculiar behavior of rational functions identified as steep gradient on one domain boundary and linear slope on the other. Whereas the rational interpolation of both elastic strain and velocity distorts solutions significantly, it is shown that the variation of solutions incurred by rational interpolation only of the elastic strain is almost negligible. It is also verified that the rational interpolation deteriorates speed of convergence with respect to mesh refinement.

Finite element analysis of planar 4:1 contraction flow with the tensor-logarithmic formulation of differential constitutive equations

  • Kwon Youngdon
    • Korea-Australia Rheology Journal
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    • v.16 no.4
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    • pp.183-191
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    • 2004
  • High Deborah or Weissenberg number problems in viscoelastic flow modeling have been known formidably difficult even in the inertialess limit. There exists almost no result that shows satisfactory accuracy and proper mesh convergence at the same time. However recently, quite a breakthrough seems to have been made in this field of computational rheology. So called matrix-logarithm (here we name it tensor-logarithm) formulation of the viscoelastic constitutive equations originally written in terms of the conformation tensor has been suggested by Fattal and Kupferman (2004) and its finite element implementation has been first presented by Hulsen (2004). Both the works have reported almost unbounded convergence limit in solving two benchmark problems. This new formulation incorporates proper polynomial interpolations of the log­arithm for the variables that exhibit steep exponential dependence near stagnation points, and it also strictly preserves the positive definiteness of the conformation tensor. In this study, we present an alternative pro­cedure for deriving the tensor-logarithmic representation of the differential constitutive equations and pro­vide a numerical example with the Leonov model in 4:1 planar contraction flows. Dramatic improvement of the computational algorithm with stable convergence has been demonstrated and it seems that there exists appropriate mesh convergence even though this conclusion requires further study. It is thought that this new formalism will work only for a few differential constitutive equations proven globally stable. Thus the math­ematical stability criteria perhaps play an important role on the choice and development of the suitable con­stitutive equations. In this respect, the Leonov viscoelastic model is quite feasible and becomes more essential since it has been proven globally stable and it offers the simplest form in the tensor-logarithmic formulation.

Excitatory Effect of Vestibular Canals on Extraocular Oblique Muscles in Rabbits (가토(家兎)에 있어서 전정반규관(前庭半規管)의 외안사근(外眼斜筋)에 관(對)한 흥분적(興奮的) 작용(作用)에 관(關)한 연구(硏究))

  • Kim, Jeh-Hyub;Park, Byung-Rim;Gill, Won-Sik
    • The Korean Journal of Physiology
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    • v.16 no.1
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    • pp.31-40
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    • 1982
  • The present experiment was carried out to elucidate interrelation between the vestibular canals and the extraocular oblique muscles. In urethane anesthetized rabbits, excitatory or inhibitory effect of the canal was produced by three different methods; selective electrical stimulation of the ampullary nerve, bidirectional (ampullofugal or ampullopetal) lymphatic fluid flow, and rapid freezing of the canal. Changes of isometric tension as well as electro-myographic activity of the oblique muscles were recorded in the ipsilateral and contralateral eyes, by means of a polygraphic recorder, and the following results were obtained. 1) Electrical stimulation of a unilateral vertical or horizontal nerve caused contraction of superior oblique muscle and relaxation of inferior oblique muscle in the ipsilateral eye, and contraction of inferior oblique muscle and relaxation of superior oblique muscle in the contralateral eye. 2) Ampullofugal flow in a vertical canal and ampullopetal flow in a horizontal canal caused the oblique muscle responses which were identical to those responses produced by the electrical stimulation of the same canal nerve. 3) Rapid freezing of a vertical canal elicited the oblique muscle responses which were opposite to those caused by electrical stimulation of the same canal nerve. From the above experimental results, functional interrelation between the individual vestibular canal and bilateral extraocular oblique muscles were better elucidated. When these results were compared to those reported by previous investigators (Utzumi, Suzuki et al.), some important discrepancies were found between them. We ascribed such discrepancies to experimental errors of the previous investigators, since their results reflected theoretical contradictions in terms of vestibular eye movements.

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Effects of Particle Size and Injector Geometry on Particle Dynamics (입자크기와 노즐형상이 입자유동특성에 미치는 영향)

  • 전운학;김종철;황승식
    • Transactions of the Korean Society of Automotive Engineers
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    • v.6 no.5
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    • pp.97-103
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    • 1998
  • The flow structure of particles for two different injectors has been investigated experimentally by means of a Phase Doppler Particle Analyzer(PDPA). Two injectors used in the present study are the pipe and contraction nozzle. Particles of 0.8${\mu}{\textrm}{m}$, 30${\mu}{\textrm}{m}$, 60 ${\mu}{\textrm}{m}$, and 100${\mu}{\textrm}{m}$ diameter were injected with a constant mass loading ratio of 0.01 and a Reynolds number of 13200. The initial mean velocity and turbulent intensity of particle are strongly influenced by the particle size and the injector geometry. The flow angles of particle at nozzle exit are sensitive to the particle size rather than the injector geometry.

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