• 한국자동차공학회논문집
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• 제9권5호
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• pp.46-53
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• 2001

To optimize the intake flow condition in the heavy-duty LPG SI engine, five different swirl ratios of intake port were investigated experimentally by oil spot method, LDV and single cylinder engine test. The flow characteristics near the piston surface were observed by oil spot method and magnitudes of swirl flow were measured quantatively by LDV method in the steady flow rig. The engine performances of various swirl flow were also tested with the heavy-duty LPG SI single cylinder engine. In the results, high swirl ratio, above $R_s$=2.3, was not suitable to develope a stable flame kernel and to produce high engine performance. Especially it was more serious under lean burn conditions, since turbulence intensity was smaller than bulk flow though those are increased together. These results were also confirmed by LDV measurement and oil spot method. On the contrary, low swirl ratio($R_s$=1.3) is not good to propagate a flame since the turbulence intensity and bulk flow are vanished during compression stroke and low swirl ratio has too weak initial energy for stable combustion. Therefore, the of optimized swirl ratio f3r the heavy-duty LPG engine in this work was found around $R_s$=2.0.

• Wind and Structures
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• 제19권2호
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• pp.113-144
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• 2014

Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.

• 한국자동차공학회논문집
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• 제24권2호
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• pp.169-182
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• 2016

This paper is the third investigation on the evaluation methods of flow characteristics in a steady flow bench. In the previous works, several assumptions used in the steady flow bench were examined and the flow characteristics were estimated both by the conventional impulse swirl meter and a particle image velocimetry at 1.75B position. From these works, it was concluded that the assumption of the solid rotation might cause serious problems and both of the eccentricity and the velocity profile distort the flow characteristics when using the ISM at 1.75B plane. Therefore, the understanding of the detail velocity profiles is very important to keep discussing the issues about the steady flow evaluation method. For this purpose, the planar velocity profiles were measure at 1.75B position by particle image velocimetry and the characteristics were examined according to the valve angles and lifts. The results show that the planar velocity profiles of 11, 16, $21^{\circ}$ valve angle heads according to the lift are similar to each other, however, that of $26^{\circ}$ angle is an exceptional case in the all aspects. In addition, the swirl behaviors are not apparent up to 6~8 mm lift under the $21^{\circ}$ angle and somewhat arranged motions are observed over the whole plane near the highest lift. At this point, the narrower the angle, the lower the lift at which the swirl motions become clear. On the other hands, when the angle is $26^{\circ}$, the center of swirl is always farthest from the cylinder center and only the indistinct swirl is observed even if at the highest lift. Also, all the swirl centers are quite apart from the cylinder center so that the effect of eccentricity may not be negligible at 1.75B regardless the valve angle. Related to the tangential velocity along with the radial direction, the bands of the velocity distribution are very wide and the mean velocities of cylinder center basis are lower than the velocity which is assumed in the ISM evaluation. Lastly, the mean tangential velocity profiles of swirl center basis are sometimes higher than that of ISM-assumed up to 0.6 non-dimensional distance less than 6mm lift, however, as the lift increases the profiles are different according to the angles and profile $11^{\circ}$ is the most closed to the ideal profile. Consequently, the real velocity profile is far from the assumption of ISM evaluation.

• 한국분무공학회지
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• 제7권1호
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• pp.14-20
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• 2002

It is well known that the flow and spray characteristics is critical factor on the performance and emission of a direct injection diesel engine. So this study aims to investigate the interaction of flow and spray characteristics. At first, in cylinder flow distributions in swirl adaptor for 4-valve cylinder head of DI Diesel engine were investigated under steady conditions for different SCV angles mounted on the cylinder head with steady rig test and 2-D LDV. And the in-cylinder flow was quantified in terms of mean flow coefficient and swirl ratio/tumble ratio. It was found that the swirl ratio is controlled between 2.3 and 3.8. Then spray characteristics of the intermittent injection were investigated. PDA system was utilized for measurement of a droplet size and velocity. The analyses of the PDA results are carried out with Time Dividing Method. It was found that there is a correlation between the swirl flow and SMD. The droplet size and the velocity were nearly constant value with each SCV angle. And the swirl ratio is higher, SMD smaller. The swirl ratio was helpful factor to the atomization of droplet.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2197-2202
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• 2006

The steady hydromagnetic flow due to a rotating disk is studied with heat transfer considering the ion slip. The governing equations are solved numerically using finite differences. The results show that the inclusion of the ion slip has important effects on the velocity distribution as well as the heat transfer.

• Ocean and Polar Research
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• 제25권spc3호
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• pp.361-371
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• 2003

The effect of bottom friction on the steady wind-driven circulation in the Yellow Sea and the East China Sea (YSECS) has been studied using a two-dimensional numerical model with and without tidal forcing. Upwind flow experiment in YSECS has also been carried out with a schematic time variation in the wind field. The surface water setup and circulation pattern due to steady wind forcing are found to be very sensitive to the bottom friction. When the effects of tidal currents are neglected, the overall current velocities are overestimated and eddies of various sizes appear, upwind flow is formed within the deep trough of the Yellow Sea, forming a part of the topographic gyre on the side of Korea. When tidal forcing is taken into account, the wind-induced surface elevations are smoothed out due to the strong tide-induced bottom friction, which is aligned almost normal to the wind stresses; weak upwind flow is farmed in the deep trough of the Yellow Sea, west and south of Jeju. Calculation with wind forcing only through a parameterized linear bottom friction produces almost same results from the calculation with $M_2$ tidal forcing and wind forcing using a quadratic bottom friction, supporting Hunter (1975)'s linearization of bottom friction which includes the effect of tidal current, can be applied to the simulation of wind-driven circulation in YSECS. The results show that steady wind forcing is not a dominant factor to the winter-time upwind flow in YSECS. Upwind flow experiment which considers the relaxation of pressure gradient (Huesh et al. 1986) shows that 1) a downwind flow is dominant over the whole YSECS when the northerly wind reaches a maximum speed; 2) a trend of upwind flow near the trough is found during relaxation when the wind abates; 3) a northward flow dominates over the YSECS after the wind stops. The results also show that the upwind flow in the trough of Yellow Sea is forced by a wind-induced longitudinal surface elevation gradient.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1457-1469
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• 2002

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.

• International Journal of Aeronautical and Space Sciences
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• 제3권1호
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• pp.95-104
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• 2002

Numerical solution of the full Navier-Stokes equation as well as the energy equation has been obtained for the unsteady natural convection in a rectangular enclosure. One side wall was maintained at very high temperature simulating fires. Especially the effect of surface radiation was taken into account. While the enclosed air was assumed to be transparent, the internal walls directly interacted one another through the surface radiation. Due to a significant temperature difference in the flow field, the equation of state was used instead of the Boussinesq approximation. It was found that the rapid heating of the adiabatic ceiling and floor by the incoming radiation from the hot wall made the evolution at thermo-fluid field highly unstable in the initial period. Therefore, the secondary cells brought about at the floor region greatly affected the heat transfer mechanism inside the enclosure. The heat transfer rate was augmented by the radiation, resulting in requiring less time for the flow to reach the steady state. At the steady state neglecting radiation two internal hydraulic jumps were clearly observed in upper/left as well as in lower/right comer. However, the hydraulic jump in the lower/right comer could not be observed for the case including radiation due to its high momentum flow over the bottom wall. Radiation resulted in a faster establishment of the steady state phenomena.

• 한국태양에너지학회 논문집
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• 제23권2호
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• pp.99-105
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• 2003

This paper presents the effect of rotor geometry on the performance of a small-scale Wells turbine for wave energy conversion. In this study, four kinds the Wells turbine of blade profile were selected from previous studies. The types of blade profile included in the papers are as follows: NACA0020 ; NACA0015; CA9; and HSIM 15-262123-1576. The experimental investigations have been performed for two solidities by testing model under steady flow conditions. The effect of blade profile on the running and starting characteristics under sinusoidal flow conditions have also been investigated by a numerical simulation based on a quasi-steady analysis. In addition, the effect of sweep on the turbine characteristics has been studied for the cases of CA9 and HSIM 15-262123-1576. Based on the evaluation, a suitable choice of these design factors has been suggested. As a result, it seems that a suitable choice of the sweep ratio of 0.35 for the blade profile of the Wells turbine.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 추계 학술대회논문집
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• pp.127-138
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• 1999

본 연구에서는 2 차원 캐비티 유동에서 경계조건 부여 방법의 차이에 따른 유체유동의 이력이 최종적인 정상상태에 미치는 효과를 수치실험을 통하여 관찰하였다. 그 결과 유동의 Reynolds 수가 작은 경우는 유동장이 가지는 이력이 시간의 경과와 함께 소멸하여 하나의 정상유동 상태를 가지는데 반하여, 큰 Reynolds 수에서는 유동장 이력이 소멸하지 않고 유지됨으로 인하여 다수의 정상유동 형태가 나타남이 확인이 되었다. 엄밀한 이론적 해석은 현재 이루워지지 않았으나 유체 운동량의 증가에 따라 Navier-Stokes 방정식의 비선형성이 영향을 미치고 있다고 여겨진다.