• 한국전산유체공학회:학술대회논문집
• /
• 2011.05a
• /
• pp.256-258
• /
• 2011

Using the axial Green's function method for Steady Stokes flows, we introduce a new pressure correction formula to satisfy the incompressibility condition, in which the pressure is related to the integral of the second order derivatives of the velocity. Based on this formula, we propose the iterative method for solving the Stokes flows in complicated domains. Even if the domain is complex, this method maintains the second order of convergence for the velocity.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.3
• /
• pp.166-173
• /
• 2007

A numerical study was conducted to have the effect of $CO_2$ addition to fuel on the chemical reaction mechanism with the change of the initial concentration of $CO_2$ and the axial velocity gradient. From this study, it was found that there were two serious effects of $CO_2$ addition on a non-premixed flame ; a diluent effect by the reactive species reduction and chemical effect of the breakdown of $CO_2$ by the third-body collision and thermal dissociation. Especially, the chemical effect was serious at the lower velocity gradient of the axial flow. It was certain that the mole fraction profile of $CO_2$ was deflected and CO was increased with the initial concentration of $CO_2$. It was also ascertained that the breakdown of $CO_2$ would cause the increasing of CO mole fraction at the reaction region. It was also found that the addition of $CO_2$ did not alter the basic skeleton of $H_2-O_2$ reaction mechanism, but contributed to the formation and destruction of hydrocarbon products such as HCO. The conversion of CO was also suppressed and $CO_2$ played a role of a dilution in the reaction zone at the higher axial velocity gradient.

• The KSFM Journal of Fluid Machinery
• /
• v.19 no.1
• /
• pp.11-17
• /
• 2016

In this paper, a numerical analysis was performed to investigate the effect of the pitch angle of a helical nozzle on the performance characteristics of a vortex tube. Three-dimensional numerical simulation has been performed with standard $k-{\varepsilon}$ turbulence model by using FLUENT 13.0. The effect of the pitch angle of helical nozzle was described in term of ${\beta}$. A CFD analysis was performed on ${\beta}=0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $15^{\circ}$. In order to realize the influence of ${\beta}$ on performances of the vortex tube. Computation results were expressed by the ${\beta}-{\Delta}T_{h,c}$ graph and radial profiles of axial velocity and swirl velocity. The results showed that ${\beta}$ which improves energy separation capacity of vortex tube was $5^{\circ}$ at ${\alpha}=0.33$, 0.5 and $10^{\circ}$ at ${\alpha}=0.33$. Besides, It was confirmed that the results were closely related to axial velocity and swirl velocity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.10
• /
• pp.1300-1308
• /
• 2000

The objectives of this study was to investigate the spray characteristics of single spray and twin spray in the overlap region such as mean axial velocity, mean radial velocity, mean droplet size and probability density function of droplet size. A phase doppler anemometer was used as the measurement system for droplet size and velocity. In case of single spray, injection pressure was varied from 0.2MPa to 0.7MPa. Mean axial velocity, mean radial velocity and droplet size were decreased as the distance below nozzle tip was increased. In case of twin spray, the spray characteristics were measured by varying the distance between two nozzles from 127mm to 155mm. In the overlap region, the boundary of the overlap region was determined by obtaining the distribution of mean axial and radial velocity. Droplet size was increased as the distance from nozzle tip was increased. It was found that the distribution of droplet size for twin spray in the overlap region was different to single spray.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.11
• /
• pp.1459-1466
• /
• 2004

The purpose of this study is to investigate the effect of swirler angle and the aspect ratio of swirl chamber of nozzle on the characteristics of single and twin spray. The characteristics of sprays have been investigated by measuring the spray angle, droplet size and velocity. Visualization of spray was conducted to obtain the spray angle and breakup process. The spray characteristics such as droplet size and velocity were measured by Phase Doppler Anemometry(PDA). It was found that the spray angle was increased with increasing the swirler angle. For both sprays, the axial velocity and SMD were decreased with increasing the swirler angle. It was also shown that the axial velocity and SMD were decreased with increasing the aspect ratio of swirl chamber, but for the twin spray, the axial velocity and SMD were not influenced significantly by the changing the aspect ratio of swirl chamber. The effect of swirler angle on the spray characteristics was greater than the aspect ratio of swirl chamber for single spray. The nozzle pitch was one of the important factors affecting the spray characteristics of twin spray.

• Journal of Power System Engineering
• /
• v.20 no.1
• /
• pp.50-56
• /
• 2016

This paper handled an investigation on the turbulent flow characteristics of three-dimensional small-size axial fan(SSAF) according to operating loads. Also, it was carried out by unsteady-state, incompressible and three-dimensional large eddy simulation(LES). The downstream flow type of SSAF is changed from axial flow to radial flow around the beginning of stall region at the aerodynamic performance curve. Axial mean velocity component largely grows around blade tip at the operating point of A to D, but transverse and vertical mean velocity components as well as Reynolds shear stresses highly develop around blade tip at the operating point of E to H. On the other hand, the peak value of turbulent kinetic energy developed around blade tip shows the highest at the operating point of E.

• Journal of the Korean Society of Visualization
• /
• v.16 no.2
• /
• pp.45-52
• /
• 2018

The tangential and axial cyclones were fabricated using a 3D printer and the total collecting efficiency, cut-diameter, and pressure drop characteristics of the two types of cyclones with the same inlet area were investigated experimentally. The results show that the total collecting efficiency tends to increase as the inlet velocity increases. However, at a 20m/s condition of the tangential cyclone, the collected particles were re-entrained to the ascending vortex flow, resulting in a decrease of the total collecting efficiency. In the axial cyclone, the cross-sectional area is designed to increase at the inlet and the velocity is reduced, so that the re-entrainment effect does not appear in this study. The pressure loss of the tangential cyclone was larger than that of the axial cyclone. The cut-diameter tends to decrease with increasing the inlet velocity in two types of cyclones, except for the 20m/s condition of the tangential cyclone.

• The Journal of the Acoustical Society of Korea
• /
• v.29 no.1E
• /
• pp.11-27
• /
• 2010

Nowadays, ultrasound Doppler imaging is widely used in assessing cardiovascular functions in the human body. However, a major drawback of ultrasonic Doppler methods is that they can provide information on blood flow velocity along the ultrasound beam propagation direction only. Thus, the blood flow velocity is estimated differently depending on the angle between the ultrasound beam and the flow direction. In order to overcome this limitation, there have been many researches devoted to estimating both axial and lateral velocities. The purpose of this article is to survey various two-dimensional velocity estimation methods in the context of Doppler imaging. Some velocity vector estimation methods can also be applied to determine tissue motion as required in elastography. The discussion is mainly concerned with the case of estimating a two-dimensional in-plane velocity vector involving the axial and lateral directions.

• Journal of Advanced Marine Engineering and Technology
• /
• v.26 no.3
• /
• pp.353-361
• /
• 2002

The tip leakage flow passing through the clearance between rotor blade tip and casing shroud has been known to occupy an important portion of the rotor overall loss. In this study, flow characteristics in axial flow rotors with different tip clearances is investigated by experimental and numerical methods. The experimental study was carried out to measure static pressure and velocity profiles at the real rotating test rig. The axial flow rotors used for the experiments have ten blades and three different rotor diameter. The tip clearance heights are 1mm, 3mm, and 4.5mm. Measurements were done using spherical type five-hole probe by non-nulling method. The numerical study was carried out to calculate pressure distributions and velocity vectors at the same condition as the experiments in the flow fields of axial flow rotors using Phoenics code.

• International Journal of Fluid Machinery and Systems
• /
• v.2 no.3
• /
• pp.223-231
• /
• 2009

Experimental investigations were conducted for the internal flows of the axial flow stator and diagonal flow rotor. Corner separation near the hub surface and the suction surface of stator blade are mainly focused on. For the design flow rate, the values of the axial velocity and the total pressure at stator outlet decrease between near the suction surface and near the hub surface by the influence of corner wall. For the flow rate of 80-90% of the design flow rate, the corner separation of the stator between the suction surface and the hub surface is observed, which becomes widely spread for 80% of the design flow rate. At rotor outlet for 81% of the design flow rate, the low axial velocity region grows between near the suction surface of rotor and the casing surface because of the tip leakage flow of the rotor.