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KSME international journal 20건

  1. [국내논문]   The Self-Induced Oscillations of the Under Expanded Jets Impinging Upon a Cylindrical Body  

    Heuy-Dong Kim ; Hideo Kashimura ; Toshiaki Setoguchi
    KSME international journal v.16 no.11 ,pp. 1448 - 1456 , 2002 , 1226-4865 ,

    초록

    The present study addresses the flow characteristics involved in the self-induced oscillations of the underexpanded jet impinging upon a cylindrical body. Both experiment and com­putational analysis are carried out to elucidate the shock motions of the self-induced oscillations and to find the associated major flow factors. The underexpanded sonic jet is made from a nozzle and a cylindrical body is placed downstream to simulate the impinging jet upon an obstacle. The computational analysis using TVD scheme is applied to solve the axisymmetric, unsteady, inviscid governing equations. A Schlieren system is employed to visualize the self -induced oscillations generated in flow field. The data of the shock motions are obtained from a high-speed video system. The detailed characteristics of the Mach disk oscillations and the resulting pressure variations are expatiated using the time dependent data of the Mach disk positions. The mechanisms of the self-induced oscillations are discussed in details based upon the experimental and computational results.

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  2. [국내논문]   Experimental Study on Axial Stratification Process and Its Effects (I) - Stratification in Engine -   피인용횟수: 7

    Ohm, In-Yong (Department, of Mechanical Engineering, Seoul National University of Technology ) , Park, Chan-Jun (Department, of Mechanical Engineering, Seoul National University of Technology)
    KSME international journal v.16 no.11 ,pp. 1457 - 1469 , 2002 , 1226-4865 ,

    초록

    This paper is the first of several companion papers, which investigate axial stratification process and its effects in an Sl engine. The axial stratification is very sophisticate phenomenon, which results from combination of fuel injection, port and in-cylinder flow and mixing. Because of the inherent unsteady condition in the reciprocating engine, it Is impossible to understand the mechanism through the analytical method. In this paper, the ports were characterized by swir and tumble number in steady flow bench test. After this, lean misfire limit of the engines, which had different port characteristic, were investigated as a function of swirl ratio and injection timing for confirming the existence of stratification. In addition, gas fuel was used for verifying whether this phenomenon depends on bulk air motion of cylinder or on evaporation of fuel. High-speed gas sampling and analysis was also performed to estimate stratification charging effect. The results show that the AFR at the spark plug and LML are very closely related and the AFR is the results of bulk air motion.

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  3. [국내논문]   Flow-Dependent Friction Loss in an Implantable Artificial Lung   피인용횟수: 1

    Lee, Sam-Cheol (Department of Advanced Materials Engineering, Hanlyo University)
    KSME international journal v.16 no.11 ,pp. 1470 - 1476 , 2002 , 1226-4865 ,

    초록

    The goal of this work is to design and build an implantable artificial lung that can be inserted as a whole into a large vein in the body with the least effect on cardiovascular hemodynamics. The experimental results demonstrate that the pressure drop is not entirely related to viscosity effects. The friction factor decreases with an increase in the number of tied-hollow fibers at a constant Reynolds number A uniform flow pattern without stagnation is observed at all numbers of tied hollow fibers tested. The tied hollow fiber module, built in this study with 3 cm of outer diameter of module. 380 m of outer diameter of tied hollow fiber, and 700 number of tied hollow fiber with length of 60 cm, which shows a pressure drop of 13-16 mmHg, satisfies the required pressure drop qualifying 15 mmHg as an intravascular artificial lung.

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  4. [국내논문]   Characterization of Thin Liquid Films Using Molecular Dynamics Simulation  

    Jaeil Lee ; Seungho Park ; Ohmyoung Kwon ; Young Ki Choi ; Joon Sik Lee
    KSME international journal v.16 no.11 ,pp. 1477 - 1484 , 2002 , 1226-4865 ,

    초록

    Various characteristics of a thin liquid film in its vapor-phase are investigated using the molecular dynamics technique. Local distributions of the temperature, density, normal and tangential pressure components, and stress are calculated for various film thicknesses and temperature levels. Distributions of local stresses change considerably with respect to film thicknesses, and interfacial regions on both sides of the film start to overlap with each other as the film becomes thinner. Integration of the local stresses, i.e., the surface tension, however, does not vary much regardless of the interfacial overlap. The minimum thickness of a liquid film before rupturing is estimated with respect to the calculation domain sizes and is compared with a simple theoretical relation.

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  5. [국내논문]   A Study on Smoke Movement in Room Fires with Various Pool Fire Location   피인용횟수: 1

    Jeong, Jin-Yong (Department of Mechanical Engineering, Chung-Ang University ) , Ryou, Hong-Sun (Department of Mechanical Engineering, Chung-Ang University)
    KSME international journal v.16 no.11 ,pp. 1485 - 1496 , 2002 , 1226-4865 ,

    초록

    In order to investigate the fire-induced smoke movement in a three-dimensional room with an open door, numerical and experimental study was performed. The center, wall, and corner fire plumes for various sized fires were studied experimentally in a rectangular pool fire using methanol as a fuel. The numerical results from a self-developed SMEP (Smoke Movement Estimating Program) field model were compared with experimental results obtained in this and from literature. Comparisons of SMEP and experimental results have shown reasonable agreement. As the fire strength became larger for the center fires, the air mass flow rate in the door, average hot layer temperature, flame angle and mean flame height were observed to increase but the doorway-neutral-planeheight and the steady-state time were observed to decrease. Also as the wall effect became larger in room fires, the hot layer temperature, mean flame height, doorway-neutral-planeheight and steady-state time were observed to increase. In the egress point of view considering the smoke filling time and the early spread of plume in the room space, the results of the center fire appeared to be more dangerous as compared with the wall and the corner fire. Thus it is necessary to consider the wall effect as an important factor in designing efficient fire protection systems.

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  6. [국내논문]   Cavitation Mode Analysis of Pump Inducer   피인용횟수: 4

    Lee, Seungbae (School of Mechanical Engineering, Inha University ) , Jung, Keun-Hwa (School of Mechanical Engineering, Inha University ) , Kim, Jin-Hwa (School of Mechanical and Aerospace Engineering, Seoul National University ) , Kang, Shin-Hyoung (School of Mechanical and Aerospace Engineering, Seoul National University)
    KSME international journal v.16 no.11 ,pp. 1497 - 1510 , 2002 , 1226-4865 ,

    초록

    The onset of cavitation causes head and efficiency of a main pump to be reduced significantly and generates vibration and noise. In order to avoid these phenomena, the inlet of the pump is fitted with a special rotor called an inducer, which can operate satisfactorily with extensive cavitation. The motivation of this study is to find out cavitation modes from the inducer inlet pressure signals and event characteristics from outlet ones at various operating conditions. The cavitation modes are analyzed by using a cross-spectral density of fluctuating pressures at the inducer inlet. The time-frequency characteristics of wall pressures downstream of the inducer are presented in terms of event frequency, its duration time, and number of events by using the Choi-Williams distribution.

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  7. [국내논문]   Time-Dependent Characteristics of the Nonequilibrium Condensation in Subsonic Flows  

    Seung-Cheol Baek ; Soon-Bum Kwon ; Toshiaki Setoguchi ; Heuy-Dong ; Kim
    KSME international journal v.16 no.11 ,pp. 1511 - 1521 , 2002 , 1226-4865 ,

    초록

    High-speed moist air or steam flow has long been of important subject in engineering and industrial applications. Of many complicated gas dynamics problems involved in moist air flows, the most challenging task is to understand the nonequilibrium condensation phenomenon when the moist air rapidly expands through a flow device. Many theoretical and experimental studies using supersonic wind tunnels have devoted to the understanding of the nonequilibrium condensation flow physics so far. However, the nonequilibrium condensation can be also generated in the subsonic flows induced by the unsteady expansion waves in shock tube. The major flow physics of the nonequilibrium condensation in this application may be different from those obtained in the supersonic wind tunnels. In the current study, the nonequilibrium condensation phenomenon caused by the unsteady expansion waves in a shock tube is analyzed by using the two-dimensional, unsteady, Navier-Stokes equations, which are fully coupled with a droplet growth equation. The third-order TVD MUSCL scheme is applied to solve the governing equation systems. The computational results are compared with the previous experimental data. The time-dependent behavior of nonequilibrium condensation of moist air in shock tube is investigated in details. The results show that the major characteristics of the nonequilibrium condensation phenomenon in shock tube are very different from those in the supersonic wind tunnels.

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  8. [국내논문]   On Constructing an Explicit Algebraic Stress Model Without Wall-Damping Function  

    Park, Noma (School of Mechanical and Aerospace Engineering, Seoul National University ) , Yoo, Jung-Yul (School of Mechanical and Aerospace Engineering, Seoul National University)
    KSME international journal v.16 no.11 ,pp. 1522 - 1539 , 2002 , 1226-4865 ,

    초록

    In the present study, an explicit algebraic stress model is shown to be the exact tensor representation of algebraic stress model by directly solving a set of algebraic equations without resort to tensor representation theory. This repeals the constraints on the Reynolds stress, which are based on the principle of material frame indifference and positive semi-definiteness. An a priori test of the explicit algebraic stress model is carried out by using the DNS database for a fully developed channel flow at Rer = 135. It is confirmed that two-point correlation function between the velocity fluctuation and the Laplacians of the pressure-gradient i s anisotropic and asymmetric in the wall-normal direction. Thus, a novel composite algebraic Reynolds stress model is proposed and applied to the channel flow calculation, which incorporates non-local effect in the algebraic framework to predict near-wall behavior correctly.

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  9. [국내논문]   An Experimental Study on Dryout Pattern of Two-Phase Flow in Helically Coiled Tubes  

    Chung, Won-Seok (School of Mechanical and Aerospace Engineering, Seoul National University ) , Sa, Young-Cheol (School of Mechanical and Aerospace Engineering, Seoul National University ) , Lee, Joon-Sik (School of Mechanical and Aerospace Engineering, Seoul National University)
    KSME international journal v.16 no.11 ,pp. 1540 - 1549 , 2002 , 1226-4865 ,

    초록

    Experimental results are presented for the effects of coil diameter, system pressure and mass flux on dryout pattern of two-phase flow in helically coiled tubes. Two tubes with coil diameters of 215 and 485 mm are used in the present study, Inlet system pressures range from 0.3 to 0.7 MPa, mass flux from 300 to 500 kg/㎡s, and heat flux from 36 to 80 kw/㎡. A partial dryout region exists because of the geometrical characteristics of the helically coiled tube. The length of the partial dryout region increases with coil diameter and system pressure. On the other hand, it decreases with increasing mass flux. The critical quality at the tube top side increases with mass flux, but decreases with increasing system pressure. This tendency is more notable when the coil diameter is larger. When the centrifugal force effect becomes stronger, dryout starts at the top and bottom sides of the tube. However, when the gravity effect becomes stronger, dryout is delayed at the tube bottom side. In some cases when the mass flux is low, dryout occurs earlier at the outer side than at the inner side of the tube because of film inversion.

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  10. [국내논문]   Application of DFB Diode Laser Sensor to Reacting Flow (Ⅰ)  

    Gyung-Min Choi ; Masashi Katsuki ; Duck-Jool Kim
    KSME international journal v.16 no.11 ,pp. 1550 - 1557 , 2002 , 1226-4865 ,

    초록

    Diode laser sensor for measuring gas temperature and species concentration in combustion chamber was developed using 2.0 μm distributed feed back lasers. To evaluate the measurement sensitivity of diode laser sensor system, CO₂ survey spectra near 2.0 μm were measured and compared with the calculated one. This diode laser absorption sensor was applied to measure gas temperatures in a premixed flat flame of CH₄-air mixture. Experimental results were in good agreement with the values by an R-type thermocouple within 6.12%. In addition, successful demonstration of measurement of gas temperature and species concentration in a soot flame showed the promising possibility of diode laser absorption sensors for practical combustion system with non-intrusive method.

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