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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Transactions of the Korean Society of Mechanical Engineers B
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Journal DOI :
The Korean Society of Mechanical Engineers
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Volume & Issues
Volume 21, Issue 12 - Dec 1997
Volume 21, Issue 11 - Nov 1997
Volume 21, Issue 10 - Oct 1997
Volume 21, Issue 9 - Sep 1997
Volume 21, Issue 8 - Aug 1997
Volume 21, Issue 7 - Jul 1997
Volume 21, Issue 6 - Jun 1997
Volume 21, Issue 5 - May 1997
Volume 21, Issue 4 - Apr 1997
Volume 21, Issue 3 - Mar 1997
Volume 21, Issue 2 - Feb 1997
Volume 21, Issue 1 - Jan 1997
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An experimental study on swirling spray flame structure by air-blast nozzle
O, Sang-Heon ; Baek, Min-Su ; Kim, Dong-Il ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 473~485
DOI : 10.22634/KSME-B.1922.214.171.1243
Detailed experimental study has been made of air blast kerosene spray flames with and without swirl in combustion air flow. Phase-Doppler detect technique is used to measure Sauter mean diameter, axial component mean and rms velocity, size-velocity correlation, and number density. These measurements are obtained for both nonreacting and reacting cases under several stable flame conditions. The results show that the introduction of swirl to the combustion air modifies the spatial distribution of droplet size, velocity, and number density, and thus alters the flame structure. However, due to the weak swirl intensity, the overall structure of swirling flames are essentially same as that of nonswirling flames. Physical model of structure of air blast atomized spray flames is projected to show that spray flames are composed of three distinct regions: the two-phase mixture region, the main reaction and the intermittent combustion region. Near the atomizer, two phase mixture of droplet and air is formed in the core region. This dense spray region is characterized by high droplet number density and the strong convective effect. There follows the main combustion region where the main flame penetrates within the spray boundary. Main reaction region of these flames are governed by internal group combustion mode. Finally there exists the intermittent combustion region where local group burning or isolated droplet burning occurs.
Temporally developing behavior of an evolving jet diffusion flame
Park, Jeong ; Sin, Hyeon-Dong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 486~493
DOI : 10.22634/KSME-B.19126.96.36.1996
Experimental investigations on the comparison of developments between transient jets and evolving jet diffusion flames have been made in initial injection period. To achieve this experiment, an ignition technique using a residual flame as the ignition source is devised. High speed Schlieren visualizations, and measurements including jet tip penetration velocities and jet widths of the primary vortex are employed to examine the developing processes for several flow conditions. It is seen that the developing behaviors in the presence of flame are greatly different from those in transient jet, and thus the flow characteristics in the transient part are also modified. The discernible differences are shown to consist of the delay of the rollup of the primary vortex, the faster spreading after the rollup due to exothermic expansion, and the survival of only a primary vortex. The growth of primary vortex in the transient jet is properly explained through an impulsively started laminar vortex prior to the interaction. It is also found that the jet tip penetration velocity varies with elapsed time and an increase in Res gives rise to a higher tip penetration velocity.
Similarity between a stagnant point diffusion flame and an evolving jet diffusion flame
Park, Jeong ; Sin, Hyeon-Dong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 494~502
DOI : 10.22634/KSME-B.19188.8.131.524
Experiments on corresponding jet flames with stagnant point diffusion flames have been carried out in initial injection periods. A compensated measurement of maximum flame temperature, which is based on the ion signal, has been employed to inspect flame responses to time-varying strain rates. The flame responses are obtained at two conditions for the slowly time-varying strain rate and the case of flame extinction, and analyzed to confirm similarity between a stagnant point diffusion flame and an evolving jet diffusion flame. Nonsteady effects are addressed via the comparison between several time scales. The time variation with low strain rates, in which illustrates the flame behavior of the upper branch far from extinction in the well-known S-curve, is confirmed to produce a quasi-steady flame response through the nonsteady experiments. The time variation with strain rates in the case of flame extinction indicates an unsteady effect of flame response. It is therefore found that the flame responses near jet tip depend on time histories of characterized strain rates in the developing process.
A study on the change of turbulence structure in a diffuser
Lee, Jang-Hwan ; Han,Yong-Un ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 503~508
DOI : 10.22634/KSME-B.19184.108.40.2063
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.
Analysis of rarefied compressible boundary layers in transition regime
Choe, Seo-Won ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 509~517
DOI : 10.22634/KSME-B.19220.127.116.119
Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.
Experimental study on flame behavior within a porous ceramic burner
Im, In-Gwon ; Jeong, Seok-Ho ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 518~524
DOI : 10.22634/KSME-B.1918.104.22.1688
Experimental studies on combustion phenomena within a porous ceramic burner are reported. Main interest of the present work is to investigate fundamental flame behaviors and their effects on the burner operation. Due to high thermal capacity of the porous ceramic materials, the response of flame to burning condition changes is slow and thus to have a stabilized flame is quite difficult and takes much time. It is found that the temperature profile obtained at downstream of the flame zone is not much sensitive to the movement of flame and the speed of flame movement is less than 0.1 mm/sec for the conditions tested. With the premixed LPG/air flame imbedded within the porous ceramic burner, stable combustion regions and unstable combustion regions leading to blowoff or flashback phenomena are observed and mapped on flow velocity versus equivalence ratio diagram. For the development of burner operation technique which is more practical and safe, intermittent burning technique, where the fuel or/and air is supplied to the burner intermittently, is proposed as one of the flame control methods for the porous ceramic burner and tested in this study. Through the experiment, it is realized that the proposed method is acceptable in respect to burner performance and give much flexibility in the operation of porous ceramic burner.
The effect of mold rotation on solidification process of an Al-Cu alloy
Yu, Ho-Seon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 525~540
DOI : 10.22634/KSME-B.1922.214.171.1245
The effect of mold rotation on the transport process and resultant macrosegregation pattern during solidification of an Al-Cu alloy contained in a vertical axisymmetric annular mold cooled from the inner wall is numerically investigated. The mold initially at rest starts to rotate at a prescribed angular velocity simultaneously with the beginning of cooling. Computed results for a representative case show that the mold rotation essentially suppresses the development of both thermal and solutal convections in the melt, creating distinct characteristics such as the liquidus front, flow pattern and temperature distribution from those for the stationary mold. Thermal convection which develops at the early stages of cooling is soon extinguished by the rotating flow induced during spin-up, and thus does not effectively remove the initial superheat from the melt. On the other hand, solutal convection, though it weakens considerably and is confined within the mushy zone, still predominates over the solute redistribution process. With increasing the angular velocity, the solute transport in the axial direction is enhanced, whereas that in the radial direction is reduced. The final macrosegregation formed in the mold rotating at moderate angular velocities appears to be favorable in comparison with the stationary casting, in that not only relatively homogenized composition is achieved, but also a severely positive-segregated channel is restrained.
Three-dimensional analysis of the flow through an axial-flow fan
Kim, Gwang-Yong ; Kim, Jeong-Yeop ; Jeong, Deok-Su ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 541~550
DOI : 10.22634/KSME-B.19126.96.36.1991
Computational and experimental investigations on the three-dimensional flowfield through an automotive cooling fan are carried out in this work. Steady, incompressible, three-dimensional, turbulent flow through a rotating axial-flow fan is analyzed with Reynolds averaged Navier-Stokes equations and standard k-.epsilon. turbulence model. The governing equations are discretized with finite-volume approximations in non-orthogonal curvilinear coordinates. Computational static pressures on the casing wall agree well with the experimental data which are measured in this work. And, they are sensitive to the change of tip clearance. The flowfield is not significantly affected by the thickness of the blade. The k-.omega. model gives the static pressure rise on the casing wall which is similar to that with the k-.epsilon. model.
Mixed convection of air in a horizontal cylindrical annulus with rotating outer cylinder
Yu, Ju-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 551~561
DOI : 10.22634/KSME-B.19188.8.131.521
Mixed convection of air in a horizontal concentric cylindrical annulus is investigated numerically. Isothermal boundary conditions are prescribed at the inner and outer cylinders, with the inner cylinder being warmer. The forced flow is induced by the outer cylinder which is rotating slowly with constant angular velocity with its axis at the center of the annulus. The effect of the forced flow on the flow pattern and heat transfer of natural convection is investigated for the annulus of (inner-cylinder radius/gap width) = 1. There appear two eddies, one eddy or no eddy according to the Rayleigh and Reynolds numbers. Map of the three flow regimes is constructed on the Ra-Re plane. (author). 28 refs., 9 figs., 2 tabs.
The effect of axial displacement of the impeller on the performance and axial thrust of a pump
Hong, Sun-Sam ; Gang, Sin-Hyeong ; Orachelashvili, B. ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 562~569
DOI : 10.22634/KSME-B.19184.108.40.2062
The axial position of an impeller is misaligned in the process of manufacturing and assembling. For a single suction centrifugal pump with balancing holes, the effect of axial displacement of impeller on the performance, leakage loss and axial thrust acting on the impeller is experimentally investigated. The axial displacement decreases the pump efficiency, increases the leakage through the clearance between wearing ring and impeller, and affects the characteristics of axial thrust.
The effects of various thermal parameters on coil temperature rise in TEFC induction motor
Yun, Myeong-Geun ; Ha, Gyeong-Pyo ; Go, Sang-Geun ; Lee, Yang-Su ; Han, Song-Yeop ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 570~578
DOI : 10.22634/KSME-B.19220.127.116.110
At design stage of new motor or when taking remedial action of old motor, a lot of information can be obtained from thermal parameters analysis. This study focused on the temperature rise of TEFC induction motor with respect to various thermal parameters. Frame heat transfer had the most important effect on coil temperature rise. But those of air gap and rotor fan had no effect. This fact shows fan action is more important than fin action in the case of rotor fan. Coil temperature can be more decreased by cooling near the heat sources than any other parts from the results of thermal conductivity and loss tests. Variation of cooling air flow rate and motor volume effects on coil temperature were also tested. These tests suggest that improvement of cooling fan performance is important in reducing the coil temperature rise. Thermal equivalent program was verified by comparison of some experimental results.
Heat transfer and flow characteristics of a circular jet impinging on a convex curved surface
Lee, Dae-Hui ; Jeong, Yeong-Seok ; Im, Gyeong-Bin ; Kim, Dae-Seong ;
Transactions of the Korean Society of Mechanical Engineers B, volume 21, issue 4, 1997, Pages 579~588
DOI : 10.22634/KSME-B.1918.104.22.1689
The heat transfer and flow measurements from a convex curved surface to a circular impinging jet have been made. The flow at the nozzle exit has a fully developed velocity profile. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the dimensionless surface curvature (d/D) from 0.034 to 0.089. The results show that the stagnation point Nusselt number (N
) increases with increasing value of d/D. The maximum Nusselt number at the stagnation point occurs at L/d .ident. 6 to 8 for all Re's and d/D's tested. For larger L/d, N
dependency on Re is stronger due to an increase of turbulence in the approaching jet as a result of the more active exchange of momentum with a surrounding air. The local Nusselt number decreases monotonically from its maximum value at the stagnation point. However, for L/d=2 and Re=23,000, and for L/d.leq.4 and Re=50,000, the stream wise Nusselt number distributions exhibit secondary maxima at r/d .ident. 2.2. The formation of the secondary maxima is attributed to an increase in the turbulence level resulting from the transition from a laminar to a turbulent boundary layer.ndary layer.