• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.2
• /
• pp.741-751
• /
• 1996

The coupled conduction and convection heat transfer from the protruding heat source in a vertical channel is numerically investigated. Conjugate solution of the two-dimensional energy equation is obtained for the incompressible air flow over the rectangular block with local heat source. It was found that several recirculation zones and separation bubble near the block were related to Re and Gr. And the results show that fractions of the heat transfer through each of the block face, maximum temperature of the block and the relative effect of each parameter on the maximum temperature and heat transfer.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.9 no.2
• /
• pp.84-91
• /
• 2001

To investigate the aerodynamic characteristics of the on a road vehicle, experimenrs were performed at an Atmospheric Boundary Layer Wind Tunnel. The scaled model of an automobile with 1 : 3 scaling ratio was used. The Reynolds number based on the free stream velocity and model length was $7.93{\times}10^5$. The influence of crosswind to the stability of automobile was investigated by the pressure distribution measurements and flow visualization studies. with the variation of the angle of attack, the change in pressure coefficient depends highly on the flow separation regimes. The experimental and numerical results are compared and found to be in good agreements.

• Korean Chemical Engineering Research
• /
• v.55 no.1
• /
• pp.130-134
• /
• 2017

Organic aerosols dispersed in the atmosphere likely undergo phase separation. Such internally mixed particles are often described as comprising an organic phase and an aqueous phase separately. We studied the morphology of two liquid separated aerosols in the sub-microscale by using a simple thermodynamic model with Russian doll geometry. The morphology of particles can be easily predicted from the simple criteria on the surface tension and two algebraic equations (the volume constraint and Young equation). This result may give the potential explanation about the complex morphology of the organic airborne particles.

• Journal of the Optical Society of Korea
• /
• v.10 no.2
• /
• pp.63-66
• /
• 2006

In microband-induced fiber gratings, polarization properties and birefringence are investigated as a function of an applied line force. With the transmission curves associated with the maximum and minimum resonant wavelengths, the polarization-dependent behaviors are analyzed. By increasing the transverse line force, the resonance wavelength for an incident light polarized to the same direction of the force is blue-shifted as much as 0.69 nm/(N/cm) while that for the other polarization is insensitive. Using the resonant wavelength separation corresponding to the force variation, the transverse effective index change or modal birefringence variation is obtained. The ratio of modal birefringence versus applied line force is ${\Delta}B/{\Delta}f_x={\sim}8.38{\times}10^{-7}$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.7
• /
• pp.945-956
• /
• 2000

The axisymmetric bodies considered in this study have hemispherical and ellipsoidal noses. The near-field pressure fluctuations over each nose model at $Re_D=2.43{\times}10^5$ were investigated in the laminar separation region and developing turbulent boundary layers using a 1/8' pin-holed microphone sensor. The wall pressure fluctuations were also measured in an axisymmetric boundary layer on a cylinder parallel to mean flow at a momentum thickness Reynolds number of 850 and a boundary layer thickness to cylinder radius ratio of 1.88.

• International Journal of Aerospace System Engineering
• /
• v.2 no.1
• /
• pp.53-57
• /
• 2015

For improving the efficiency of near space propellers working over 20km, performances of their streamwise sections, i.e. low-Reynolds-number airfoils which work at $10^4-10^5$ Reynolds numbers, are significant. Based on the low-Reynolds-number CFD technology, this paper designs a novel low-Reynolds-number airfoil. Unsteady characteristics of the laminar separation bubble on novel airfoil and a typical conventional airfoil are studied numerically, and the Reynolds number effect is investigated. Results show that at $10^4-10^5$ Reynolds numbers, unsteady aerodynamic characteristics of the novel airfoil are severely weakened and its lift-to-drag ratio can increase about 100%.

• International Journal of Aerospace System Engineering
• /
• v.2 no.1
• /
• pp.6-11
• /
• 2015

An active flow control technique using blowing and distributed suction on low Reynolds airfoil is investigated. Simultaneous blowing and distributed suction can recirculate the jet flow mass, and reduce the penalty to propulsion system due to avoiding dumping the jet mass flow. Energy is injected into main flow by blowing on the suction surface, and the low energy boundary flow mass is removed by distributed suction, thus the flow separation can be successfully suppressed. Aerodynamic lift to drag ratio is improved significantly using the flow control technique, and the energy consumption is quite low.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1998.04a
• /
• pp.15-15
• /
• 1998

The problem of the impingement of a sonic or a supersonic jet on a flat surface has not only wide applications but has also interesting and very complex flow phenomena. The main applications of this impinging jet include prediction of solid surface erosion, design of launcher systems, stage separation of multi-stage rocket system, V/STOL operations, thermal spray system, and manufacturing technologies of materials. Much have been learned about the supersonic impinging jet flow field but many fundamental questions have not been answered satisfactorily. The problem encompasses many facets of fluid dynamics which, in combination, present the compressibility effect and the viscous-inviscid interaction, coupled with flow separation and reattachment. What is more, there are many flow parameters that have on the impinging jet flow field, for example, Mach number, Reynolds number, pressure ratio, distance between the nozzle exit and flat plate, jet shock structure, nozzle diameter and etc. Thus the existing data on the supersonic impinging jet flow present considerable disagreement in which quantitative comparison between one result and another is often impossible.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2017.05a
• /
• pp.379-382
• /
• 2017

Flow characteristics of dual bell nozzle with pintle were investigated. Thrust and thrust coefficient were compared with the pintle-bell nozzle of the same condition, and difference according to the pintle stroke was investigated. At stroke 0 mm, the thrust of the dual bell nozzle was about 13.18% higher than the bell nozzle, and when the pintle was backward, it was similar to the bell nozzle. The change in expansion ratio with stroke was considered to be more advantageous for a dual bell nozzle that performs altitude compensation through separation and transition.

• Korean Journal of Applied Biomechanics
• /
• v.13 no.1
• /
• pp.23-38
• /
• 2003

The purpose of this study is to develop an improved marker auto-identification algorithm for reduce of data processing time through improve the efficiency of noise elimination and marker separation. The maker auto-identification algorithm was programming named KUMAS used Delphi language. For the study, various experiments were conducted for the verification of KUMAS. and compared two systems of established with the KUMAS. Four different motions - cycling, gait, rotation, and pendulum -, were selected and tested. Motions were filmed 30Hz frames rate per second. ${\chi}^2$ used for statistical analysis. Significant level were ${\alpha}=.05$. The test results were as follow. 1. Increased the success ratio of marker auto-identification. 2. The efficiency of marker auto-identification was remarkably improved through marker separation, noise elimination. 3. The marker auto-identification ability was improved in 2D-image plane include the 3D motion. 4. Significant different were found between KUMAS and B-SYS(established system) with non-input the artificial noise frames, input the artificial noise frames and total frames.