• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.23 no.2
• /
• pp.86-94
• /
• 1987

In order to examine the flow motion in a combustion chamber of a motored diesel engine, the variation of instantaneous are velocity at a fixed point in combustion chamber was measured by the constant temperature hot wire anemometer, varing engine speed, shroud shape and shroud position. The results are summerized as follows: 1. The variation of air velocity in a combustion chamber is closely related with the valve timing and piston velocity. 2. The air velocity in the cylinder at suction stroke is being increased and maximized at 60$^{\circ}$ ABDC in compression stroke and then decreased at the e.v.o. in expansion stroke. 3. The mean velocity using shroud valve was less than no shroud valve. However the turbulent intensity using shroud valve was larger than no shroud valve. 4. The turbulent intensity with 90$^{\circ}$shroud valve was larger than that of 120$^{\circ}$shroud valve, and 90$^{\circ}$shroud valve at 180$^{\circ}$shroud position had the largest turbulent intensity.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.23 no.2
• /
• pp.40-40
• /
• 1987

In order to examine the flow motion in a combustion chamber of a motored diesel engine, the variation of instantaneous are velocity at a fixed point in combustion chamber was measured by the constant temperature hot wire anemometer, varing engine speed, shroud shape and shroud position. The results are summerized as follows: 1. The variation of air velocity in a combustion chamber is closely related with the valve timing and piston velocity. 2. The air velocity in the cylinder at suction stroke is being increased and maximized at 60° ABDC in compression stroke and then decreased at the e.v.o. in expansion stroke. 3. The mean velocity using shroud valve was less than no shroud valve. However the turbulent intensity using shroud valve was larger than no shroud valve. 4. The turbulent intensity with 90°shroud valve was larger than that of 120°shroud valve, and 90°shroud valve at 180°shroud position had the largest turbulent intensity.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.5B
• /
• pp.529-537
• /
• 2006

This paper investigates the impacts of the drag-related weighting coefficients on mean velocity and turbulence structures. The transport equations for the Reynolds stress of vegetated open-channel flows are derived by using the temporal- and horizontal-averaging scheme. It is found that the total Reynolds stress of vegetated open channel flows consists of the Reynolds stress due to temporally fluctuating velocities and the Reynolds stress due to spatially fluctuating velocities. The drag-related weighting coefficient $C_{fk}$ for the total Reynolds stress component is found to be unit, while the coefficient for the Reynolds stress due to temporally fluctuating velocities can be negligible. This is the reason why very small weighting coefficients in previous studies yield very good agreements with measured data. In other words, the Reynolds stress due to spatially fluctuating velocities remains still unknown, especially due to the large number of measuring locations. Through a developed Reynolds stress model, vegetated open-channel flows are simulated and compared with measured data from the literature. Comparisons reveal that the computed mean flow and Reynolds stress structures are hardly affected by the drag-related weighting coefficients. However, the computed turbulence intensity profiles are significant different with the drag-related weighting coefficients. A budget analysis of the transport equations for the Reynolds stress component is carried to investigate why turbulence intensity is affected by the drag-related weighting coefficients.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.746-751
• /
• 2001

We used a cylindrical model which simulates turbine blade leading edge to investigate the effects of free-stream turbulence intensity and blowing ratio on film cooling of turbine blade leading edge. Tests are carried out in a low-speed wind tunnel on a cylindrical model with three rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was $7.1\times10^4$. Two types of turbulence grid are used to increase a free-stream turbulence intensity. The effect of coolant blowing ratio was studied for various blowing ratios. For each blowing ratios, wall temperatures around the surface of the test model are measured by thermocouples installed inside the model. Results show that blowing ratios have small effect on spanwise-averaged film effectiveness at high free-stream turbulence intensity. However, an increase in free-stream turbulence intensity enhances significantly spanwise-averaged film effectiveness at low blowing ratio.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.1 no.1
• /
• pp.1-13
• /
• 1993

The three-dimensional numerical analysis for in-cylinder flow of four-valve engine without intake port has been successfully computed. These computations have been performed using technique of the general coordinate transformation based on the finite-volume method and body-fitted non-orthogenal grids using staggered control volume and covariant variable as dependent one. Computations are started at intake valve opening and are carried through top-dead-center of compression. A k-$\varepsilon$model is used to represent turbulent transport of momentum. The principal study is the evolution of interaction between mean flow and turbulence and of the role of swirl and tumble in generating near TDC turbulence. Results for three different inlet flow configuration are presented. From these results, complex flow pattern may be effective for promoting combustion in spark-ignition engines and kinetic energy of mean flow near TDC is well converted into turbulent kinetic energy.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.2 no.2
• /
• pp.12-23
• /
• 1994

In order to investigate the effect of turbulent intensity on combustion characteristics, new flame factor model was developed. The principal study is the evaluation of interaction of swirl, tumble and unstrutural component of flow characteristics and correlation between turbulent intensity and flame factor. Computational and experimental study has been, performed such as quasi-dimensional cycle simulation, three dimensional flow analysis, engine performance test and diagnostic simulation. From these studies, it was found that flame factor was a function of engine speed and turbulent intensity.

• Journal of the KSME
• /
• v.33 no.12
• /
• pp.1063-1068
• /
• 1993

왕복식엔진에서 연소과정은 실린더내 유체유동에 지배되므로 최적조건의 엔진설계를 위해서는 실린더내 유체유동을 효과적으로 이용하는 것이 필요하다. 연소과정에 중요한 영향을 미치는 압축말기 연소실내 난류강도는 흡입과정시 생성된 유동의 에너지가 압축과정을 거치면서 작은 스케일의 에디(eddy)로 깨지면서 발생된다. 연소과정시 이러한 에디들은 초기화염생성을 촉진 시키고 화염전파속도를 증진시키는 역할을 함으로써 실린더내 유체유동에 대한 이해증진을위해 실린더내 평균속도 및 난류유동을 측정하는 연구들이 많이 진행되고 있다. 엔진유동은 매사이 클의 유동이 엄밀히 주기적인 운동을 하지 않고, 각 사이클의 유동이 비정상유동을 하며, 유동의 생성 및 소멸이 매우 짧은 특성을 가진다. 따라서 산란입자가 측정체적을 통과할 때 속도데이 터가 발생하는 LDV(laser Doppler velocimetry) 측정에 있어서 레이저빔의 산란광노이즈 감소와 산란입자의 효율적인 공급으로 데이터 발생률을 높이는 것이 어려운 점이다. 이 글에서는 엔진 유동의 LDV측정시 고려해야 할 문제점들, 실험장치구성, 그리고 데이터처리 방법과 주요측정 결과에 대해 본 연구팀에서 지금까지 수행한 연구결과를 토대로 하여 기술하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.1
• /
• pp.110-120
• /
• 1986

45.deg. corss jet flow, at the mixing of two jet flows, was experimentally studied. For this study, only the statistical turbulent characteristics and high order moments will be analysed by on-line computer system (hot-wire anemometer system, dynamic analyser and computer system, plotting and printing system). Since mean velocity distributions, intensities of turbulence, Reynolds stresses, correlation coefficients, and other general results were already studied and presented. One dimensional probability density distributions of u', v', and w' were analysed comparing with Gaussian curve, which showed skew and flat tendency according to the Y and Z directions. For the analysis of the joint flow of turublent components, the joint probability density distributions were examined. The fagures were drawn so as to be read joint probabilities, joint probability densities, fluctuating velocities u', v', and w'. For further detailed examination of the variations of skewness and flatness phenomena, iso-joint probability density contours obtained from the profiles of the joint probability density distributions were studied. According to the displacement of positions from the center of the mixing flow and the directions, the flatness and skewness factors were increased.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.3
• /
• pp.540-546
• /
• 1992

Turbulent Couette flow between coaxial cylinders with inner one rotating has been investigated experimentally and numerically. The radius ratio of the coaxial cylinders is 0.43. Mean velocity and turbulent stresses have been measured by hot-wire anemometer in the range of Reynolds number based on the velocity at rotating wall and the radial distance between walls, 60,900-187,000. For the numerical computation, the Reynolds stress model has been used as a turbulence closure model. Measurements of mean velocity show that the velocity profile of wall layer largely deviates from universal logarithmic law due to the effect of streamline curvature, especially in the region near the stationary outer cylinder. The results computed with the Reynolds stress model agree well with the experimental data in the prediction of circumferential intensity of turbulent fluctuations. However, the computed level of radial intensity is much higher than the measurement. Curvature-corrected versions of the Reynolds stress model improves the prediction of turbulent intensities, but the results are not fully satisfactory.

• Journal of Advanced Marine Engineering and Technology
• /
• v.21 no.1
• /
• pp.43-48
• /
• 1997

The present study is aimed to investigate experimentally on the hydrodynamic behaviours of air ~ pulverized coal flow in rectangular combustor with cavity. Mean velocity, density and tur¬bulent properties of pulverized coal in rectangular entrained flow combustor were measured by PDA. Experimental results show that the flow reattachment point at the lower plane in the com¬buster chamber has been developed near X/D= 15. The similarities at each section are found after the flow reattachment point. The maximum values of turbulent intensity and Reynolds shear stress have been shown near Y/D=6, which is higher than centerline. The maximum density of the pulverized coal sited in the range ofY/D=6~8.