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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
Journal Basic Information
Journal DOI :
The Korean Society of Mechanical Engineers
Editor in Chief :
Volume & Issues
Volume 22, Issue 7 - Jul 1998
Volume 22, Issue 6 - Jun 1998
Volume 22, Issue 5 - May 1998
Volume 22, Issue 4 - Mar 1998
Volume 22, Issue 3 - Mar 1998
Volume 22, Issue 2 - Feb 1998
Volume 22, Issue 1 - Jan 1998
Volume 22, Issue 10 - 00 1998
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Numerical simulation of the flow behind a circular cylinder with a rotary oscillation
Baek, Seung-Jin ; Seong, Hyeong-Jin ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 267~279
DOI : 10.22634/KSME-B.19184.108.40.2067
A numerical study was made of flow behind a circular cylinder in a uniform flow, where the cylinder was rotationally oscillated in time. The temporal behavior of vortex formation was scrutinized over broad ranges of the two externally specified parameters, i.e., the dimensionless rotary oscillating frequency (.110.leq.
.leq..220) and the maximum angular amplitude of rotation (.theta.
=15 deg., 30 deg. and 60 deg.). The Reynolds number (Re=
.nu.) was fixed at Re=110. A fractional-step method was utilized to solve the Navier-Stokes equations with a generalized coordinate system. The main emphasis was placed on the initial vortex formations by varying
. Instantaneous streamlines and pressure distributions were displayed to show the vortex formation patterns. The vortex formation modes and relevant phase changes were characterized by measuring the lift coefficient (
) and the time of negative maximum
) with variable forcing conditions.s.tions.s.s.s.
Numerical analysis of a turbulent boundary layer with pressure gradient using Reynolds-transport turbulence model
Lee, Seong-Hyeok ; Yu, Hong-Seon ; Choe, Yeong-Gi ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 280~293
DOI : 10.22634/KSME-B.19220.127.116.110
Numerical study on turbulent and mean structures of a turbulent boundary layer with longitudinal and spanwise pressure gradient is carried out by using Reynolds-stress-model (RSM). The existence of pressure gradient in a turbulent boundary layer causes the skewing or divergence of rates of strain, which contributes to production of turbulent kinetic energy. Also, this augmentation of production due to extra rates of strain can increase the turbulent mixing and cause the anisotropy of turbulent intensities in the outer layer. This paper uses the Reynolds Stress Model to capture anisotropy of turbulent structures effectively and is devoted to compare the results computed by using RSM and the standard k-.epsilon. model with experimental data. It is concluded that the RSM can produce the more accurate predictions for capturing the anisotropy of turbulent structure than the standard k-.epsilon. model.
Ignition of a solid fuel by thermal radiation
Kim, Myeong-Hyo ; Baek, Seung-Uk ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 294~302
DOI : 10.22634/KSME-B.1918.104.22.1684
Ignition characteristics of a vertical solid fuel plate with block have been investigated experimentally. For low radiant heat flux, ignition does not occur in a vertical solid fuel plate without block. In the case with the block on a vertical fuel plate, however, ignition can occur by increasing the residence time and the time to absorb the incident radiation flux by fuel vapor in gas phase. The ignition occurs below block and the point varies according to the block location and the block height. As the block height increases, the block locates at higher position, and the hot wall temperature increases, the ignition delay time decreases. Also as the initial temperature of fuel plate rises, the ignition delay time of the solid fuel plate decreases. The temperature distribution of solid fuel plate with block is nearly proportional to the radiant heat flux distribution. Therefore, the effect temperature by natural convection heat transfer is of the same order as that of inhibition of temperature increase by pyrolysis.
Operating characteristics of a heat pipe with two heat sources
Park, Jong-Heung ; No, Hong-Gu ; Lee, Jae-Heon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 303~315
DOI : 10.22634/KSME-B.1922.214.171.1243
Numerical and experimental studies on a heat pipe with two heat sources have been performed to investigate the operating characteristics. Numerical analysis was performed based on the cylindrical two-dimensional incompressible laminar flow for the vapor space and the conjugate heat transfer for the entire heat pipe. Experimental study with a 0.45 m length copper-water heat pipe was also performed to validate the numerical modeling for the heat input range from 29 W to 47 W on each heater. As results, the temperature profiles at the outer wall for the single active heat source as well as the temperature profiles for the switching operation between two heat sources are suggested. Due to the axial conduction, it is found that the temperature drop between the evaporator and the condenser appears small when the heat source closer to the condenser is turned on. For the switching operation in the present study, the transient time is about 700s and the temperatures at the locations of both heat source are same in 130s after switching.
The role of large-scale structures in mixing layers
Seo, Tae-Won ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 316~325
DOI : 10.22634/KSME-B.19126.96.36.1996
The objective of this study is to investigate the role of large-scale coherent structures in a spatially developing plane mixing layers. To achieve this, we have to look into the mutual interactions between three-dimensional large-scale coherent structures and the mean flow. Our attention will be focused on the energy exchange mechanism between the various modes, and the effects of the nonlinear evolution of the phases of the interacting modes. Linear stability of the three-dimensional viscous shear layer is formulated and solved as the basis for the solution of the nonlinear formulation based on the energy method. The importance of the initial conditions that may affect the evolution of the flow has been examined. It has been numerically calculated the nonlinear effects arising from the interactions among the three-dimensional large-scale coherent structures in a spatially developing plane mixing layers. The results of this study provide useful parametric information for the control of shear layer in practical applications in the mixing and transport augmentation.
Numerical calculation of torque converter flow using interrow mixing model
Park, Jae-In ; Jo, Gang-Rae ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 326~335
DOI : 10.22634/KSME-B.19188.8.131.526
In this study, a steady three-dimensional incompressible turbulent flow within a torque converter was numerically analyzed with the introduction of interrow mixing model. Mixing planes were introduced to exchange the flow informations between two adjacent elements of the torque converter. The mixing planes were installed among three elements of the torque converter. Therefore, in the present method, it could be possible to calculate the flow-filed within the torque converter without any assumption of circulating flow rates or any extension of boundaries toward the upstream and the downstream for each element. The numerically calculated performances of the torque converter were in good agreement with experimental results, and the complex flow patterns were be observed according to design and off-design condition. As a conclusion, it was found that the present numerical method was very effective in the steady flow analysis of torque converters.
축류회전차 익말단 틈새유동에 대한 수치해석
No, Su-Hyeok ; Jo, Gang-Rae ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 336~345
DOI : 10.22634/KSME-B.19184.108.40.2066
The substantial loss behind axial flow rotor was generated by wake, various vortices in the hub region and the leakage vortex in the tip region. Particularly, the leakage vortex formed near blade tip was one of the main causes of the reduction of performance, the generation of noise and the aerodynamic vibration in rotor downstream. In this study, the three-dimensional flowfields in an axial flow rotor for various tip clearances were calculated, and the numerical results were compared with the experimental ones. The numerical technique was based on SIMPLE algorithm using standard k-.epsilon. model (WFM). Through calculations, the effects of the tip clearance on the overall performance of rotor and the loss distributions, and the increase in the displacement, momentum, and blade-force-deficit thickness of the casing wall boundary layer were investigated. The mass-averaged flow variables behind rotor agreed well with the experimental results. The presence of the tip leakage vortex behind rotor was described well. Although the loci of leakage vortex by calculation showed some differences compared with the experimental results, its behavior for various tip clearances was clarified by examining the loci of vortex center.
Control effects of the flow and the aerodynamic force around the downstream cylinder by a spinning upstream cylinder in uniform flow
Bu, Jeong-Suk ; Yang, Jong-Pil ; Kim, Chang-Su ; Sin, Yeong-Gon ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 346~359
DOI : 10.22634/KSME-B.19220.127.116.116
The aerodynamic forces and wake structure of the non-rotating downstream circular cylinder, of which the uniform freestream flow is interfered with another spinning upstream cylinder having the same diameter that is located upstream in a line have been investigated experimentally. When the spin rate of the downstream cylinder defined as the ratio of tangential surface velocity of the spinning cylinder to the freestream velocity increases gradually from zero to 1.4, the change of surface pressure distribution, aerodynamic forces of the non-rotating downstream cylinder were measured in case of several distance ratios of 1.5, 3.0, and 4.5 defined as the ratio of distance between the centers of two cylinders to the diameter. The wake flow patterns behind the cylinder were also investigated in each case. From the present experiments, it has been found that the spin rate significantly influences the aerodynamic forces and near-wake flow phenomena of the downstream cylinder in such a way that the drag increases as the spin rate and distance ratio increase and the wake width increases as the distance ratio increases.
A numerical study of natural convection for low Pr liquids in enclosures with rocking
Mo, Jeong-Ha ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 360~372
DOI : 10.22634/KSME-B.1918.104.22.1680
This study deals with the interaction between buoyancy-induced convection and externally imposed excitation in the form of harmonic rocking and the effect of the interaction upon heat transfer in low-Pr liquids. A wide array of system responses are discussed using the spectral collocation numerical technique. The superposition of buoyancy and Coriolis forces leads to complex fluid flow and heat transfer. The transition to chaotic convection is accelerated, and heat transfer rates are reduced as the enclosure is excited at the fundamental frequency of oscillation associated with the pure buoyancy-driven case. Average heat transfer rates are correlated for Pr=0.02 and 0.03. The heat transfer is affected more in the Pr=0.03 liquid than the case of Pr=0.02.
Heat transfer coefficient measurement by a jet impinging on a rib-roughened convex surface
Jeong, Yeong-Seok ; Lee, Dae-Hui ; Lee, Jun-Sik ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 373~385
DOI : 10.22634/KSME-B.1922.214.171.1243
The local Nusselt numbers have been measured for a round turbulent jet impinging on the convex surface with and without rib. Liquid crystal/transient method was used to determine the Nusselt number distributions along the surface. The temperature on the surface was measured to within .+-.0.25 deg. C accuracy using liquid crystal and a digital color image processing system. The experiments were made for the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 6 to 10, the dimensionless surface curvature (d/D) 0.056, and the various rib types (height(d
) from 1 to 2 mm, pitch (p) from 6 to 32 mm). It was found that the average Nusselt numbers on the convex surface with rib are higher than those without rib, mainly due to an increase in the turbulent intensity caused by flow separation, recirculation and reattachment on the wall surface. In addition, we compared the results by the steady-state method using the gold-film Intrex with those by the transient method.
Heat Transfer Characteristics on Impingement Surface with Control of Axisymmetric Jet(I)
Lee, Chang-Ho ; Kim, Yeong-Seok ; Jo, Hyeong-Hui ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 386~398
DOI : 10.22634/KSME-B.19126.96.36.1996
The present experiment is conducted to investigate heat transfer characteristics on the impinging surface with secondary flows around circular nozzle jets. The changed vortex pattern around jet affects significantly the flow characteristics and heat transfer coefficients on the impinging surface. The effects of the jet vortex control are also considered with jet nozzle-to-plate distances and main jet velocities. The vortex pattern around a jet is changed from a convective instability to an absolute instability with a velocity suction ratio of the main jet and the secondary counterflow. With the absolute instability condition, the jet potential core length increases and the heat transfer on the impinging surface is increased by small scale eddies. The region of high heat transfer coefficients is enlarged with the high Reynolds number due to increasing secondary peak values. The effect of suction flows is influenced largely with collars attached the exit of the jet nozzle because the attached collar guides well the counterflow around the main jet.
Numerical study of a coating with pigment to selectively reflect the thermal radiation from fire
Byeon, Do-Yeong ; Baek, Seung-Uk ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 399~407
DOI : 10.22634/KSME-B.19188.8.131.529
The infrared reflection coatings with pigment can be used to protect the surfaces of combustible materials exposed to fire. To obtain high reflectivities in the infrared range (0.5-10.mu.m) important to fire, several dielectric pigments, such as titanium dioxide, iron oxide, and silicon, can be synthesized to polymer coatings. The theoretical analysis shows that the coating design with particles diameter in the 1.5 to 2.5.mu.m range and volume fraction in the 0.1 to 0.2 range is estimated to be optimal. In the analysis of the radiation, the dependent scattering, absorption by polymeric binder, and the internal interface reflection are considered. In addition, the temperature distribution in the semi-transparent coating layer and an opaque substrate (PMMA) is also presented.
An experimental study on the dynamic characteristics of a residential air-conditioner with a R22 alternative refrigerant
Kim, Man-Hoe ;
Transactions of the Korean Society of Mechanical Engineers B, volume 22, issue 3, 1998, Pages 408~415
DOI : 10.22634/KSME-B.19184.108.40.2068
This study presents experimental results on the shut-down and start-up characteristics of a residential split-system air-conditioner with capillary tube, using R410A as a R22 alternative refrigerant. During shut-down, the transient characteristics are evaluated by measuring the high side and low side pressures and temperatures of the system. The dynamic behavior of the system after start-up is also investigated at the high temperature cooling test condition. All experiments are performed in psychrometric calorimeter. The cooling capacity, power consumption, dehumidification capacity and cycle characteristics after start-up are analyzed.