• Title/Summary/Keyword: flow field simulation

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CFD Analysis of Aerodynamic Characteristics of a BWB UCAV configuration with Transition effect (천이효과를 고려한 BWB UCAV 형상의 공력 특성 전산해석)

  • Jo, Young-Hee;Chang, Kyoungsik;Sheen, Dong-Jin;Park, Soo Hyung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.42 no.7
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    • pp.535-543
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    • 2014
  • A computational simulation for a nonslender BWB UCAV configuration with rounded leading edge and span of 1.0m was performed to analyze its aerodynamic characteristics. The freestream is 50m/s over -4 to 26 degree A.o.A.s. Reynolds number based on the mean chord length is $1.25{\times}10^6$. 3D multi block hexahedral grids are used which allow good grid quality and ease to capture boundary layer. ${\gamma}-Re_{\theta}$ model as well as $k-{\omega}$ SST model is employed to assess the effect of transition for flow behavior. Drag and lift of the UCAV were well predicted while $C_M$ is under predicted at high angle of attacks and influenced by the turbulence models strongly. After assessing pressure distribution, skin friction lines and velocity field around the UCAV configuration, it was found that transition effect should be considered to enhance the prediction of aerodynamic behavior by a vortical flowfield.

Slat Noise Source Modeling of Multi-element Airfoil in High-lift Configuration

  • Hwang, Seung Tae;Han, Chang Kyun;Im, Yong Taek;Kim, Jong Rok;Bae, Youngmin;Moon, Young J.
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.2
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    • pp.197-205
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    • 2017
  • We investigate the slat noise generation mechanism by using large-eddy simulation (LES) and simple source modeling based on linearized Euler equations. An incompressible LES of an MD 30P30N three-element airfoil in the high-lift configuration is conducted at $Re_c=1.7{\times}10^6$. Using the total derivative of the hydrodynamic pressure (DP/Dt) acquired from the incompressible LES, representative noise sources in the slat cove region are characterized in terms of simple sources such as frequency-specific monopoles and dipoles. Acoustic radiation around the 30P30N multi-element airfoil is effectively computed using the Brinkman penalization method incorporated with the linearized Euler equation. The directivity pattern of $p^{\prime}_{rms}$ at $r=20c_{slat}$ in the multiple sources is closely compared to that obtained by the application of the LES/Ffowcs-Williams and Hawking's methods to the entire flow field. The power spectrum of p' at ${\theta}=290^{\circ}$ is in good agreement with the data reported in BANC-III, especially the broadband part of the spectrum with a decaying slope ${\propto}f^{-3}$.

Simulation of Field Soil Loss by Artificial Rainfall Simulator - By Varing Rainfall Intensity, Surface Condition and Slope - (인공강우기에 의한 시험포장 토양유실량 모의 - 강우강도, 지표면 및 경사조건 변화 -)

  • Shin, Minhwan;Won, Chul-hee;Choi, Yong-hun;Seo, Jiyeon;Lee, Jaewoon;Lim, KyoungJae;Choi, Joong-dae
    • Journal of Korean Society on Water Environment
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    • v.25 no.5
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    • pp.785-791
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    • 2009
  • Using artificial rainfall simulator, the soil loss, which is deemed as the most cause of muddy water problem among Non-point source (NPS) pollutant, was studied by the analysis of direct runoff, groundwater discharge, and soil water storage properties concerned with rainfall intensity, slope of area, and land cover. The direct runoff showed increasing tendency in both straw covered and bared soil as slope increases from 5% to 20%. The direct runoff volume from straw covered surface were much lower than bared surface. The infiltration capacity of straw covered surface increased, because the surface sealing by fine material of soil surface didn't occur due to the straw covering. Under the same rainfall intensity and slope condition, 2.4~8.2 times of sediment yield were occurred from bared surface more than straw covered surface. The volume of infiltration increased due to straw cover and the direct runoff flow decreased with decrease of tractive force in surface. To understand the relationship of the rate of direct runoff, groundwater discharge, and soil water storage by the rainfall intensity, slope, and land cover, the statistical test was performed. It shows good relationship between most of factors, except between the rate of groundwater storage and rainfall intensity.

Fluid-structure Interaction Analysis of Large Sandwich Panel Structure for Randomly Distributed Wind Load considering Gust Effects (거스트 영향이 고려된 랜덤 분포 풍하중에 대한 대형 샌드위치 패널 구조물의 유체-구조 연성해석)

  • Park, Dae Woong
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.12
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    • pp.1035-1044
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    • 2013
  • Because of the high specific stiffness and strength inherent in the sandwich structure composed of facesheet that resists in-plane loads and a core that resists out-of-plane loads, it is often used for large and light-weighted structures. However, inevitably the increased flexibility allows greater deformation-based disturbances in the structures. Thus, it is necessary to analyze the structural safety. To obtain more accurate analytical results, the input disturbances must more closely simulate real load conditions; to improve accuracy, non-linear elements such as gust effects were considered. In addition, the structural safety was analyzed for the iso-grid sandwich panel structure using fluid-structure interactions. For a more realistic simulation, flow velocity fields, which consider the effects of irregular gust fluctuation, were generated and the coupled field was analyzed by mapping the pressure and displacement.

INVESTIGATION OF THE OPERATIONAL PRINCIPLE AND PARAMETRIC STUDY ON A DRY PASTE SEPARATOR EQUIPED WITH A ROTOR - I. THEORETICAL STUDY (로터 장착 건식 미분 분리기의 작동원리 규명 및 파라미터 연구 -I. 이론 해석)

  • Park, S.U.;Kang, Y.S.;Kang, S.;Suh, Y.K.
    • Journal of computational fluids engineering
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    • v.20 no.4
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    • pp.70-80
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    • 2015
  • Construction waste is known to include a large part of coarse and fine aggregates, which can be recirculated in the industry. Separating those aggregates economically from the waste has been thus considered to be one of the most important issues in this field. In particular, paste mixed in the waste causes significant complain from the inhabitants living near the place where waste-processing equipments are built and operated. In this study, we investigate the operational principle of a newly developed paste separator by using theoretical (in this first part) and CFD (in the second part) analysis. The separator consists of a rotor which turned out to play a significant role in separating those pastes from the aggregates. Under suitable assumptions regarding the air flow velocity as well as the particle velocity, we show that particles can be stagnant at the outlet of the roto channel for a wide range of parameter values, which allow the particles to get enough time to settle down via the gravitation. We also demonstrate such phenomenon by using a simple numerical simulation.

Eulerian-based Numerical Modeling for Impingement Prediction of Supercooled Large Droplets (과냉각대형액적 충돌예측을 위한 오일러리안 기반 수치 모델링)

  • Jung, Sung-Ki;Kim, Ji-Hong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.8
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    • pp.647-654
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    • 2012
  • Supercooled large droplet issues in aircraft icing have been continually reported due to the important safety considerations. In order to simulate the impingement behavior of large droplets, a two-dimensional and compressible Navier-Stokes code was developed to determine the flow field around the test model. Also, the Eulerian-based droplet impingement model including a semi-empirical approach for the droplet-wall interaction process and droplet break-up was developed. In particular, the droplet-wall interactions were considered as numerical boundary conditions for the droplet impingement simulation in the supercooled large droplet conditions. Finally, the present results were compared with the experimental test data and the LEWICE results. The droplet impingement area and maximum collection efficiency values between present results and wind tunnel data were in good agreements. Otherwise, the inclination of collection efficiency of the present result is over-predicted than the wind tunnel data around a lower surface of the NACA 23012 airfoil.

Traffic Signal Control Methods for Functional Improvements in COSMOS (COSMOS 안정화를 위한 교통축 및 감응제어 방법연구)

  • 이승환;오영태;이상수
    • Journal of Korean Society of Transportation
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    • v.20 no.6
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    • pp.31-43
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    • 2002
  • Traffic signal control methods are suggested to improve the operational effectiveness of COSMOS system in Seoul. First. a method that improves progression of the corridor traffic flow within a common sub-area was explored. Applying this method, both frequency and magnitude of offset transition were reduced as compared to the existing method. In addition, the level of connection among neighboring corridors increased by applying the method, thus the qualify of progression was also improved. Second, a practical guideline on signal phase design was proposed to improve the efficiency of actuated operations for the left-turn movement. Last, a method for estimating optimal queue length parameters was surveyed and evaluated. An evaluation study was performed for the suggested methods through both field and simulation studies. Results showed that the proposed methods gave better performance than the existing methods. It is expected that the use of proposed methods can improve operational performance of COSMOS.

Wave Modeling considering Water Level Changes and Currents Effects (수위변화와 흐름효과를 고려한 파랑모델링)

  • Eum, Ho-Sik;Kang, Tae-Soon;Nam, Soo-Yong;Jeong, Won-Moo
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.28 no.6
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    • pp.383-396
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    • 2016
  • In this study, wave model was conducted on the presence or absence of water level changes and currents effects in coastal waters coexisting with waves and currents, then the results were compared. The flow field applied the results of the RIAMOM model and the wave model applied the SWAN model. Among ECMWF, NCEP and JMA, wind data applied JMA data sets which agreed well with the observed data comparatively. Numerical simulation was conducted for 8 months from January to August 2016. For each case, the deviation of wave height was calculated for the high wave of more than 2.5 m for comparison with observed data. As a result, the deviation of wave height was not significant both considering water level changes and currents effects or not at wave observation stations installed in deep waters. However, a significant deviation of wave height of 5~10% was obtained depending on water level changes and currents effects at the comparison point in shallow waters.

Scour around Piers in the Stage Hydrograph (수위변화에 따른 교각주위에서의 세굴현상연구)

  • An, Sang-Jin;Yeon, Gi-Seok
    • Journal of Korea Water Resources Association
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    • v.30 no.4
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    • pp.335-346
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    • 1997
  • This study aims at examining closely the scour around a pier due to irregular water stage changes during flood. At the Sangye bridge is located lowermost downstream of the Bocheong stream in the Kum River, the IHP experimental watershed. For this purpose, we have analyzed the change of scour depths due to stage hydrographs of experimental basin by a simulation. To examine the scour phenomenon around a pier due to irregular stage change in flood, we have analyzed the change of scour depth corresponding to stage hydrograph of field watershed after verification of model channel. From this study, the following conclusions are made: First, in case of predicting the maximum scour depth around a pier with stage hydrograph in the state of steady flow, we should choose the highest stage. Second, after increasing the stage, the equilibrium scour depth became smaller than the maximum scour depth. Therefore, in case of estimating the maximum scour depth in rivers, it is recommended that we should consider additional scour depth with is reduced by infilling the sediments.

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Two-Dimensional Hydrodynamic and Water Quality Simulations for a Coinjunctive System of Daecheong Reservoir and Its Downstream (대청호와 하류하천 연속시스템의 2차원 수리·모의)

  • Jung, Yong Rak;Chung, Se Woong;Ryu, In Gu;Choi, Jung Kyu
    • Journal of Korean Society on Water Environment
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    • v.24 no.5
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    • pp.581-591
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    • 2008
  • Most of our rivers are fragmented by the presence of at least one large dam. Dams are often the most substantial controller of the flow regimes and aquatic environments of natural river system. The quality of downstream water released from a stratified reservoir is highly dependent on upstream reservoir water quality. Thus, an integrated modeling approach is more efficient, compared to fragmented modeling approach, and necessary to better interpret the impact of dam operation on the down stream water quality. The objectives of this study were to develop an integrated reservoir-river modeling system for Daecheong Reservoir and its downstream using a two-dimensional laterally averaged hydrodynamic and water quality model, and evaluate the model's performance against field measurement data. The integrated model was calibrated and verified using filed data obtained in 2004 and 2006. The model showed satisfactory performance in predicting temporal variations of water stage, temperature, and suspended solid concentration. In addition, the reservoir-river model showed efficient computation time as it took only 3 hours for one year simulation using personal computer (1.88 Ghz, 1.00 GB RAM). The suggested modeling system can be effectively used for assisting integrated management of reservoir and river water quality.