• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.302-312
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• 2004

This work developed improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan. Both steady and unsteady three-dimensional CFD analyses were performed to validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the present model takes into account the effect of blade curvature. The correction method is provided to predict mass-averaged absolute circumferential velocity at the exit of impeller by taking account of blockage effects induced by the large-scale backflow near the front plate and flow separation within blade passage. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peak total pressure coefficient.

• Environmental Engineering Research
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• v.10 no.1
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• pp.15-21
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• 2005

A computer program is developed for the prediction of the flow pattern and the removal efficiency of suspended solid (SS) in a circular secondary clarifier. In this study the increased density effect by SS on hydrodynamics has been systematically investigated in terms of Froude Number (Fr), baffle existence, and a couple of important empirical models associated with the particle settling and Reynolds stresses. A control-volume based-finite difference method by Patankar is employed together with the SIMPLEC algorithm for the resolution of pressure-velocity coupling. The k-ε turbulence and its modified version are incorporated for the evaluation of Reynolds stresses. The calculation results predicts well the overall flow pattern such as the waterfall phenomenon at the front end of the clarifier and the bottom density current with the formation of strong recirculation especially for the case of decrease of Fr. Even if there are some noticeable differences in the prediction of two turbulence models, the calculated results of the radial velocity profiles are generally in good agreement against experimental data appeared in open literature. Parametric investigation has been systematically made with the Fr and baffle condition with detailed analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.657-665
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• 2003

Several interesting results were obtained from the flow visualization experiment in the accompanying paper, Part I. in the present study, Part II, a numerical study has been carried out to explain the detailed flow phenomena in micro-channel filling process. Hele-Shaw flow approximation was applied to the micro-channel geometry based on the small characteristic length. And surface tension effect has been introduced on the flow front as the boundary condition with the help of a dynamic contact angle concept between the melt front and the wall. A dimensional analysis for numerical results was carried out and a strong relationship between dimensionless pressure and Capillary number is obtained. The numerical analysis results are compared with the flow visualization experimental observations. And the numerical system developed in the present study seems to be able to predict the interesting micro-channel filling flow characteristics observed from experiments.

• Tunnel and Underground Space
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• v.32 no.3
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• pp.203-218
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• 2022

A hydro-mechanical study was performed to analyze the relationship between the magnitude of injection-induced seismicity and shut-in. In hydraulic analysis, the suspension of fluid injection makes the pore pressure gradient smaller while the pore pressure at the pressure front can reach the critical value for several hours after shut-in, which leads to the additional slip with wider area than during injection. The hydro-mechanical numerical analysis was performed to model the simplified fault system, and simulated the largest magnitude earthquake during shut-in stage. The effect of the abrupt suspension of fluid injection on the large magnitude earthquake was investigated in comparison with the continuous injection. In addition to the pore pressure distribution, it was found that the geometry of multiple faults and the stress redistribution are also important in evaluating the magnitude of the induced seismicity.

• International Journal of Highway Engineering
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• v.10 no.1
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• pp.41-48
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• 2008

This paper deals with the characteristics of earth pressure to the debris-fall prevention walls which usually are installed in front of steep slope. Such walls have narrow backfill width where the active soil wedge can not be developed fully. The earth pressure to such walls ue affected by the movement of wall and arching effects due to the friction developing on the surface of adjacent ground slope and wall and therefore cannot be analyzed and calculated reliably. The study is carried out through laboratory model tests using centrifuge test. Test results reveal that the earth pressure to the debris-fall prevention wall depends largely on the inclination angle of the ground slope and the wall movement. The earth pressure reduction due to wall movement was observed at the upper half of wall, while the arching effect was significant at the lower half especially in the case of steep ground slope. It can be said that from the result of this study in the design of a debris-fall prevention wall the earth pressure should be determined considering the inclination of ground slope and the condition of wall movement during and after construction.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.1
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• pp.57-62
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• 2011

The effects of swirl chamber's diameter and length on injector's dynamic characteristics were investigated through an experimental study. A mechanical pulsator was installed in front of the manifold of a swirl injector which produces pressure oscillations in the feed line. Pressure in the manifold, liquid film thickness in the orifice and the pressure in the orifice were measured in order to understand the dynamic characteristic of the simplex swirl injector with varying geometry. A direct pressure measuring method (DPMM) was used to calculate the axial velocity of the propellant in the orifice and the mass flow rate through the orifice. These measured and calculated values were analyzed to observe the amplitude and phase differences between the input value in the manifold and the output values in the orifice. As a result, a phase-amplitude diagram was obtained which exhibits the injector's response to certain pressure fluctuation inputs. The mass flow rate was calculated by the DPMM and measured directly through the actual injection. The effect of mean manifold pressure change was insignificant with the frequency range of manifold pressure oscillation used in this experiment. Mass flow rate was measured with the variation of injector's geometries and amplitude of the mass flow rate was observed with geometry and pulsation frequency variation. It was confirmed that the swirl chamber diameter and length affect an injector's dynamic characteristics. Furthermore, the direction of geometry change for achieving dynamic stability in the injector was suggested.

• Journal of computational fluids engineering
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• v.19 no.2
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• pp.66-71
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• 2014

Aerodynamic design of a vehicle has very important meaning on the fuel economy, dynamic stability and the noise & vibration of a moving vehicle. In this study, the correlation of aerodynamic effect between two model vehicles moving inline on a road was studied with the basic SAE model vehicle. Drag and lift are two main physical forces acting on the vehicle and both of them directly effect on the fuel economy and driving stability of the vehicle. For the research, the distance between two vehicles is varied from 5m to 30m at the fixed vehicle speed, 100km/h and the side-wind was assumed to be zero. The main issue for this numerical research is on the understanding of the interaction forces; lift and drag between two vehicles formed inline. From the study, it was found that as the distance between two vehicles is closer, the drag force acting on both the front and rear vehicle decreases and the lift force has same trend for both vehicle. As the distance(D) is 5m, the drag of the front vehicle reduced 7.4% but 28.5% for the rear-side vehicle. As the distance is 30m, the drag of the rear vehicle is still reduced to 22% compared to the single driving.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.95-105
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• 2018

Increasing cruise speed is an important issue for the development of the next generation rotorcraft. Among several concepts proposed by previous research, the rotorcraft with ducted fan demonstrates its possibility of high-speed flight. In this study, numerical simulations are conducted to investigate the aerodynamic and flow characteristics of multi-ducted fan in forward flight. The aerodynamic efficiency around front ducted fan is determined by interaction between free-stream velocity and the induced velocity. While flow characteristics of rear ducted fan are dominantly influenced by the front ducted fan. Separation in the front ducted fan occurs faster than that of rear ducted fan, and the separation at duct inlet induces an increase of fan thrust. As a result of interaction effect between each ducted fan, relatively aligned inflow enters to the rear ducted fan. Therefore, thrust of the rear fan is decreased steadily before separation, and sudden changes of thrust in fans occur simultaneously. Due to the pressure decrease on lower surface, the normal force of rotorcraft is reduced with forward speed.

• Journal of the Korean Geotechnical Society
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• v.28 no.2
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• pp.71-78
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• 2012

Rainfall infiltration test under one dimensional condition is conducted to evaluate the effect of rainfall intensity on seepage velocity and infiltration characteristics for initial unsaturated sediment. Experimental results are compared with those numerical simulations with respect to variations of pore water pressure, degree of saturation and discharge velocity with time, and both results give good agreement. High rainfall intensity tends to increase seepage velocity almost linearly. But it shows rapid increase as rainfall intensity approaches saturated hydraulic conductivity of the sediment. In addition, the upper part of wetting front depth is partially saturated, not fully. Therefore, actual wetting front depth is considered to advance faster than theoretical prediction, which leads to slope instability of unsaturated slope due to surface rainfall.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1137-1143
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• 1994

Through the numerical analysis of the capillary pressure-based Richards equation with and without the effect of the capillary hysteresis under the boundary condition having an antecedent rainfall. the moving tendency of the wetting front, the redistribution of the moisture content, infiltration rate, cumulative infiltration etc, were computed. The effect of the capillary hysteresis cannot be neglected in analyzing an unsaturated flow, and the more accurate results may be obtained by the consideration of the hysteresis effect. If the effect of the hysteresis cannot be considered, the analysis by the use of the main wetting curve may give more reliable result than that of the main drying curve.