• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.790-798
• /
• 2008

Counter-rotating axial flow fan(CRF) consists of two counter-rotating rotors without stator blades. CRF shows the complex flow characteristics of the three-dimensional, viscous, and unsteady flow fields. For the understanding of the entire core flow in CRF, it is necessary to investigate the three-dimensional unsteady flow field between the rotors. This information is also essential to improve the aerodynamic characteristics and to reduce the aerodynamic noise level and vibration characteristics of the CRF. In this paper, experimental study on the three-dimensional unsteady flow of the CRF is performed at the design point(operating point). Flow fields in the CRF are measured at the cross-sectional planes of the upstream and downstream of each rotor using the $45^{\circ}$ inclined hot-wire. The phase-locked averaged hot-wire technique utilizes the inclined hot-wire, which rotates successively with 120 degree increments about its own axis. Three-dimensional unsteady flow characteristics such as tip vortex, secondary flow and tip leakage flow in the CRF are shown in the form of the axial, radial and tangential velocity vector plot and velocity contour. The phase-locked averaged velocity profiles of the CRF are analyzed by means of the stationary unsteady measurement technique. At the mean radius of the front rotor inlet and the outlet, the phase-locked averaged velocity profiles show more the periodical flow characteristics than those of the hub region. At the tip region of the CRF, the axial velocity is decreased due to the boundary layer effect of the fan casing and the tip vortex flow. The radial and the tangential velocity profiles show the most unstable and unsteady flow characteristics compared with other position of rotors. But, the phase-locked averaged velocity profiles of the downstream of the rear rotor show the aperiodic flow pattern due to the mixture of the front rotor wake period and the rear rotor rotational period.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.807-812
• /
• 2001

The effects of casing shapes on the interaction of the impeller and volute in a small-size turbo-compressor are investigated. Numerical analysis is conducted for the compressor with circular and single volute casings from inlet to discharge nozzle. In order to predict the flow pattern inside the entire impeller, vaneless diffuser, and casing, calculations with a multiple frame of reference method between the rotating and stationery parts of the domain are carried out. For incompressible turbulent flow fields, the continuity and three-dimensional time-averaged Navier-Stokes equations are employed. To predict the performance of two types of casings, the static pressure and loss coefficients are obtained with various flow rates. Also, static pressure distributions around casings are studied for different casing shapes, which are very important to predict the distribution of radial load.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.27 no.2
• /
• pp.13-20
• /
• 1990

The interaction of the flows induced by stator blades with a ship-like wake is discussed to obtain the flow components of each with and without radial shear. The flow induced by stator blades is modeled by lifting line theory and the shear is taken to be provided by the radial gradient of the peripheral mean axial flow approximated by a logarithmic function of radius for a class of vessels. And the theory is based on the linearized Euler equations in the absence of viscosity. The results show that shear effects are relatively large at inner radii and the distribution of blade pitch angles is most effective in reducing non-uniformity.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.29 no.3
• /
• pp.220-228
• /
• 1993

This paper presents a description and evaluation of a detailed mathematical simulation for the steady and unsteady flow in a radial inflow-turbine which is most frequently used, at present, for exhaust gas turbochargers of internal combustion engines. As a method of computation, the two-step differential Lax-Wendroff method and the characteristic method were used. The turbine characteristics, the mass flow rate, the power output and fluid movements at the turbine scroll inlet were compared with the experiment data. The results of the simulation were in good agreement with experimental values under both steady and unsteady flow conditions.

• 유체기계공업학회:학술대회논문집
• /
• 1999.12a
• /
• pp.227-233
• /
• 1999

Detailed Measurements were made to investigate the turbulence characteristics of a leakage vortex in an axial-flow fan using three-dimensional LDV. The turbulence in the leakage vortex has highly anisotropic characteristics with the radial value being the maximum. The turbulence intensity components in the vortex in the streamwise and tangential directions increase up to a certain downstrean position and then decrease. This increase is mainly due to the rapid decrease of the streamwise velocity of the vortex and partly due to the radial gradient of the streamwise velocity caused by a velocity deficit. As the vortex decays moving downstream, turbulence intensity also decrease gradually.

• Journal of Biomedical Engineering Research
• /
• v.15 no.2
• /
• pp.143-150
• /
• 1994

Wall shear rate or stress is believed to be a major hemodynamic variable influencing atherosclerosis and artery-graft anastomic intimal hyperplasia. The purpose of this study is to verify the effects of radial wall motion, artery-graft compliance and diameter mismatch, and impedance phase angle on the wall shear rate distribution near an end-to-end artery-graft anastomosis model. The results show that radial wall motion of the elastic artery model lowers the mean wall shear rates under pulsatile flow condition by 15 to 20 % comparing to those under steady flow condition at the same mean flow rate. Impedance phase angle seems to have small effects on the mean and amplitude of the wall shear rate distribution. In order to study the effects of compliance and diameter mismatch on the wall shear rates, two models are studied-Model I has 6% and Model I has 6% and Model II has 11% smaller graft diameter. Divergent geometry caused by diameter mismatch near the distal sites reduces the mean wall shear rates significantly, and this low shear region is believed to be prone to intimal hyperplasia.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2012.05a
• /
• pp.104-105
• /
• 2012

The design of coaxial porous injector was suggested to improve the mixing and atomizing performance at the center region of the conventional 2-phase flow coaxial shear injector spray. Several cold flow tests of 2-dimensional injectors was performed, and the gas injection area was varied to determine the effect of the magnitude of gas radial momentum.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.7
• /
• pp.735-743
• /
• 2015

The major component with a significant impact on the thermodynamic efficiency of the organic Rankine cycle is the turbine. Many difficulties occur in the turbine design of an organic Rankine cycle because the expansion process in an organic Rankine cycle is generally accompanied by a dramatic change in the working fluid properties. A precise preliminary design for a radial inflow turbine is hard to obtain using the classic method for selecting the loading and flow coefficients from the existing performance chart. Therefore, this study proposed a method to calculate the loading and flow coefficient based on the number of rotor vanes and thermodynamic design requirements. Preliminary design results using the proposed models were in fairly good agreement with the credible results using the commercial preliminary design software. Furthermore, a numerical analysis of the preliminary design results was carried out to verify the accuracy of the proposed preliminary design models, and most of the dependent variables, with the exception of the efficiency, were analyzed to meet the preliminary design conditions.

• Journal of Soil and Groundwater Environment
• /
• v.7 no.4
• /
• pp.17-23
• /
• 2002

Pumping tests were carried out from seven wells in fractured rocks. The time-drawdown data were obtained from pumping wells and corrected for the elapsed time of step drawdown test using Cooper-Jacob's method. A statistical method. the least square of error, was used to yield the coefficient of aquifer losses, the coefficient of well losses, and the power which indicates the severity of the turbulence. The values of the power range from 1.65 to 6.48. The well losses result mainly from turbulent flow caused by radial flow nearby pumping wells. The turbulent flow depends on Reynolds number. Since the hydraulic characteristics of fractured rocks control the fluid velocity, the value of the power is an important factor to understand the aquifer system of fractured rocks.

• Journal of Chest Surgery
• /
• v.37 no.10
• /
• pp.839-844
• /
• 2004

Background: The Y-composite graft of internal thoracic artery and radial artery is commonly used in coronary bypass surgery. The aim of this study is to look for a way to raise the free flow of the internal thoracic graft and to see flow dynamics of the Y-graft. Material and Method: In 15 patients undergoing coronary bypass surgery, free flow of the in-situ internal thoracic artery graft was measured using two different papaverine application methods; extraluminal papaverine spray in 7 patients and intraluminal papaverine injection in 8. In 18 other patients for whom the Y-graft was used, total free flow and flow changes from the two ends were measured. Result: The free flow of the in-situ internal thoracic artery graft almost doubled with internal papaverine injection than with external papaverine spray $(47.7\pm9.6$ mL/min $vs.100.8\pm26.3$ mL/min, p<0.001). Total flow of the Y-composite graft was significantly more than either flow of the internal thoracic artery end or radial artery graft end $(173.3\pm45.3$ mL/min vs. $121.1\pm34.3$ mL/min or $117.5\pm42.8$ mL/min). When both ends of the Y-composite graft were opened, free flows from the two ends were similar $(85.4\pm27.8$ mL/min vs: $87.9\pm42.4$ mL/min, p=0.772). The flow of one end of the Y-composite graft was increased significantly by clamping of the other-end than when both ends were opened. Conclusion: Intraluminal papaverine injection is very effective in raising free flow of the internal thoracic artery graft, and the free flow of the Y-composite graft of in-situ internal thoracic artery and free radial artery graft is more than that of the in-situ internal thoracic artery graft. The flow of one end flow of the Y-graft may be altered by the flow change of the other end.