• Journal of Energy Engineering
• /
• v.14 no.1
• /
• pp.30-36
• /
• 2005

This paper reports the experimental study of the heat transfer characteristics of the wake region behind a cylinder in cross flow. Local heat transfer coefficient was measured from the stagnation point (θ=0°) to 180°, and the variation of Nu in the axial direction along the cylinder was also studied. The results show that the heft transfer rate at the rear (θ=180°) near the duct wall can increase as much as 58% over the 2 dimensional value at the center of the duct. The heat transfer profiles in the wake region also show distinct effects of the aspect ratio and the heat transfer boundary condition.

• The Journal of Engineering Geology
• /
• v.32 no.4
• /
• pp.535-545
• /
• 2022

Improving the stability of the ground in seismic design requires an understanding of the dynamic behavior of the ground under seismic loads. The shaking table test is an important methodology to provide this understanding. This study aimed to assess the influence on boundary conditions, as they are among the most important factors affecting the test. This was achieved by testing the influence of boundary conditions on the seismic responses of model slopes at different locations in the testing apparatus. A model slope was fabricated at different locations in a laminar shear box, and the influence of the boundary conditions was then measured. Each model slope was created at 100, 50, and 25 cm from the soil wall, and sine wave seismic loads of the same size were inputted. The results confirmed that the acceleration was amplified by the influence of the boundary in the case of the slope being located 25 cm from the boundary, whereas the influence of the boundary conditions decreased when the slope was located at 50~100 cm.

• Journal of the Korean Society of Visualization
• /
• v.20 no.1
• /
• pp.52-63
• /
• 2022

Direct numerical simulation of blood flow in a stenosed, patient-specific carotid artery was conducted to explore the transient behavior of blood flow with special emphasis on the wall-shear stress distribution over the transition region. We assumed the blood as an incompressible Newtonian fluid, and the vessel was treated as a solid wall. The pulsatile boundary condition was applied at the inlet of the carotid. The Reynolds number is 884 based on the inlet diameter, and the maximum flow rate and the corresponding Womersley number is approximately 5.9. We found the transitional behavior during the acceleration and deceleration phases. In order to quantitatively examine the wall-shear stress distribution over the transition region, the probability density function of the wall-shear stress was computed. It showed that the negative wall-shear stress events frequently occur near peak systole. In addition, the oscillatory shear stress index was used to further analyze the relationship with the negative wall-shear stress appearing in the systolic phase.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1933-1938
• /
• 2004

Nucleate boiling experiments with constant wall temperature of heating surface were performed using R113 for almost saturated pool boiling conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain a constant wall temperature condition and to measure the heat flow rate with high temporal and spatial resolutions. Bubble images during the bubble growth were taken as 5000 frames a sec using a high-speed CCD camera synchronized with the heat flow rate measurements. The geometry of the bubble during growth time could be obtained from the captured bubble images. The bubble growth behavior was analyzed using the new dimensionless parameters for each growth regions to permit comparisons with previous results at the same scale. We found that the new dimensionless parameters can describe the whole growth region as initial and later respectively. The comparisons showed good agreement in the initial and thermal growth regions. The required heat flow rate for the volume change of the observed bubble was estimated to be larger than the instantaneous heat flow rate measured at the wall. Heat, which is different from the instantaneous heat supplied through the heating wall, can be estimated as being transferred through the interface between bubble and liquid even with saturated pool conditions. This phenomenon under a saturated pool condition needs to be analyzed and the data from this study can supply the good experimental data with the precise boundary condition (constant wall temperature).

• Structural Engineering and Mechanics
• /
• v.68 no.2
• /
• pp.237-245
• /
• 2018

This study proposes an empirical formulation to predict the maximum deformation of offshore blast wall structure that is subjected to impact loading caused by hydrocarbon explosion. The blast wall model is assumed to be supported by a simply-supported boundary condition and corrugated panel is modelled. In total, 1,620 cases of LS-DYNA simulations were conducted to predict the maximum deformation of blast wall, and they were then used as input data for the development of the empirical formulation by regression analysis. Stainless steel was employed as materials and the strain rate effect was also taken into account. For the development of empirical formulation, a wide range of parametric studies were conducted by considering the main design parameters for corrugated panel, such as geometric properties (corrugation angle, breadth, height and thickness) and load profiles (peak pressure and time). In the case of the blast profile, idealised triangular shape is assumed. It is expected that the obtained empirical formulation will be useful for structural designers to predict maximum deformation of blast wall installed in offshore topside structures in the early design stage.

• 한국전산유체공학회:학술대회논문집
• /
• 1998.11a
• /
• pp.160-166
• /
• 1998

In this paper, incompressible two-dimensional Navier-Stokes equations are numerically solved for the study of steady laminar flow around a body with the wall effect. A second-order finite difference method is used for the spatial discretization on the nonstaggered grid system and the 4-stage Runge-Kutta scheme for the numerical integration in time. The pressure field is obtained by solving the pressure-Poisson equation with the Neumann boundary condition. To investigate the wall effect, numerical computations are carried out for the NACA 0012 section at the various blockage ratios. The pressure and skin friction on the foil surface, velocity pronto in its wake and drag coefficient are investigated as functions of the blockage ratio.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.10 s.253
• /
• pp.987-995
• /
• 2006

A reversed trapezoidal fin with the fluid in the inside wall is analyzed and optimized in this study. As a fin base boundary condition, the heat transfer from inside wall fluid to the fin base is considered. The values of fin base temperature with the variations of inside wall fluid convection characteristic number and fin base length are listed. The heat transfer, fin effectiveness, fin length and fin base height are optimized as a function of fin base length, convection characteristic number ratio, fin shape factor and fin volume.

• Journal of the korean Society of Automotive Engineers
• /
• v.4 no.2
• /
• pp.69-78
• /
• 1982

The purpose of this study is to investigate the flame propagation phenomenon in the combustion chamber of spark-ignition gasoline engine for the idling condition. by means of four ion probes located through the cylinder head, the time intervals for the flame to arrive at the respective probes are read on th visicorder char. As results, the flame is considered to initiate after some ignition delay and to propagate through the central space of combustion chamber with rather constant speed on the order of 25m/sec, and thereafter to be slowed down approaching the wall. Additionally, the retardation of flame in the wall boundary layer could be inferred. The maximum pressure is developed when the flame nearly touches the wall diagonal to the spark plug. And some features of flame propagation are elucidate.

• Proceedings of the KSME Conference
• /
• 2008.11b
• /
• pp.2995-3000
• /
• 2008

Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, the wall impact behavior of an electrically charged drop has been investigated and compared with that of a neutral drop experimentally. The critical Sommerfeld number representing the spread-splash boundary for the charged drop impacting on the dielectric substrate turned out to be larger compared to that for the neutral drop with the same surface condition. The change of the transition boundary is due to the increase in the surface wettability of the drop on the substrate. However, with the electrically conducting substrates, the charging effect on the transition boundary appeared negligible. This is because the electric discharging time is much shorter than the time required for the flattened drop to reach its maximum extent.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.2
• /
• pp.287-298
• /
• 1989

A numerical work was performed to study the flow behaviors of the open channel type flow with its geometric boundary conditions being similar to that of the Multi-Stage-Flash evaporator with and without a baffle. For the analysis, two-dimensional steady turbulent flow was assumed and the widely known k-.epsilon. turbulence model was usded. SIMPLE algorithm and the power difference scheme were used for the numerical approach. Numerical results generally agree with the previous experimental results though there are some uncertainties at far downstream and near the free surface due to the three dimensionality of the flow and surface waves. Without a baffle, the flow has basically the shape of the submerged plane wall jet with its upper boundary at downstream being sharply curved toward the free surface. For the flow with a baffle, recirculation flow patterns are observed at the upper inlet portion and at the backside of the baffle. For the case without a baffle, it was also confirmed that the ratio between the liquid level and the gate opening height is the most important parameter to determine the flow behavior.