• Title/Summary/Keyword: sub stream

Search Result 348, Processing Time 0.025 seconds

A study on CIM construction for the plastic fan design manufacturing (플라스택 팬 설계, 제조의 CIM 구축을 위한 연구)

  • Choi, Yang-Ho;Lee, Yong-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.21 no.9
    • /
    • pp.1470-1479
    • /
    • 1997
  • In this study, the plastic fan with high efficiency and low noise was designed and the capacity of the wind and the wind pressure were analysed and verified by CAE. After designing the metallic mold using the metallic mold design data, and the the metallic mold design was reformed by analysing the process of the material stream and injection filling by CAE. Also the metallic mold cutting data were formed using the metallic mold design data. These cutting data was used to produce the fan electrode by a machining center and then this electrode were used to manufacture the metallic mold by cutting the fan cavity by an electrical spark machine. The purpose of this study is to find out the sub-optimal condition on the productivity and improvement in quality of the plastic fan by integrating a series of this process with a computer.

Large eddy simulation of a square cylinder flow: Modelling of inflow turbulence

  • Tutar, M.;Celik, I.
    • Wind and Structures
    • /
    • v.10 no.6
    • /
    • pp.511-532
    • /
    • 2007
  • The present study aims to generate turbulent inflow data to more accurately represent the turbulent flow around a square cylinder when the inflow turbulence level is significant. The modified random flow generation (RFG) technique in conjunction with a previously developed LES code is successfully adopted into a finite element based fluid flow solver to generate the required inflow turbulence boundary conditions for the three-dimensional (3-D) LES computations of transitional turbulent flow around a square cylinder at Reynolds number of 22,000. The near wall region is modelled without using wall approximate conditions and a wall damping coefficient is introduced into the calculation of sub-grid length scale in the boundary layer of the cylinder wall. The numerical results obtained from simulations are compared with each other and with the experimental data for different inflow turbulence boundary conditions in order to discuss the issues such as the synthetic inflow turbulence effects on the 3-D transitional flow behaviour in the near wake and the free shear layer, the basic mechanism by which stream turbulence interacts with the mean flow over the cylinder body and the prediction of integral flow parameters. The comparison among the LES results with and without inflow turbulence and the experimental data emphasizes that the turbulent inflow data generated by the present RFG technique for the LES computation can be a viable approach in accurately predicting the effects of inflow turbulence on the near wake turbulent flow characteristics around a bluff body.

Estimation of Design Flood Runoff in Ungaged Forest Watershed to Reduce Flood Damage within the National Park (국립공원내 홍수피해 저감을 위한 미계측 산림지역의 설계홍수량 추정)

  • Kim, Sang-Min;Im, Sang-Jun;Lee, Sang-Ho;Kim, Hyung-Ho;Ma, Ho-Seop;Jeong, Won-Ok
    • Journal of The Korean Society of Agricultural Engineers
    • /
    • v.51 no.5
    • /
    • pp.107-113
    • /
    • 2009
  • The purpose of this study is to estimate the design flood runoff for ungaged forest watershed to reduce the flood damage in national park. Daewonsa watershed in Jirisan National Park was selected as study watershed, of which characteristic factors were obtained from GIS data. Flood runoff was simulated using SCS unit hydrograph module in HEC-HMS model. SCS Curve Number (CN) was calculated from forest type area weighted average method. Huff's time distribution of second-quartile storm of the Sancheong weather station, which is nearest from study watershed, was used for design flood runoff estimation. Critical storm duration for the study watershed was 3 hrs. Based on the critical duration, the peak runoff for each sub-watershed were simulated. It is recommended to monitor the long-term flow data for major stream stations in National Park for a better reliable peak runoff simulation results.

LARGE EDDY SIMULATION OF THE COMPRESSIBLE FLOW OVER A CAVITY WITH HIGH ASPECT RATIO

  • Oh Keon Je
    • Journal of computational fluids engineering
    • /
    • v.9 no.1
    • /
    • pp.1-9
    • /
    • 2004
  • Large eddy simulation is used to investigate the compressible flow over a cavity with high aspect ratio. The sub-grid scale stresses are modeled using the dynamic model. The compressible Navier-Stokes equations are solved with the sixth order accurate compact finite difference scheme in the space and the 4th order Runge-Kutta scheme in the time. The buffer Bone techniques are used for non-reflecting boundary conditions. The results show the shear layer oscillation over the cavity. The votical disturbances, the roll-up of vorticity, and impingement and scattering of vorticity at the downstream cavity edge can be seen in the shear layer. Several peaks for the resonant frequencies are found in the spectra of the vertical velocity at the center-line. The most energetic Peak near the downstream edge is different from that at the center part of the cavity The pressure has its minimum value in the vortex core inside the cavity, and becomes very high at the downstream face of the cavity. The variation of the model coefficient predicted by the dynamic model is quite large between 0 and 0.3. The model coefficient increases in the stream-wise evolution of the shear layer and sharply decreases near the wall due to the wall effect.

Calculation of the mean flow past circular cylinders using an improved separation model (개선된 박리 모델을 이용한 원통 주위 유동장 계산)

  • 최도형;신승용
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.11 no.6
    • /
    • pp.877-883
    • /
    • 1987
  • A new improved inviscid separation model to calculate the mean flow past circular cylinders is proposed. The wake region is modeled by a pair of vortex sheets which emerge from the separation points and are allowed to move freely with the local stream. The vortex strength assumes a constant value for some initial distance which is related to the pressure drag and gradually decreases to zero as the sheet moves farther away from the body. This vorticity distribution automatically takes care of the length parameter which has been one of the deficiencies in the existing models. The procedure is tested against various experimental data and the agreement is quite good for both sub and super-critical regimes. The comparison with an existing model is also given.

Analyzing the urban surface temperature characteristic before Cheong-Gye stream restoration using thermal infrared of ASTER image (ASTER 열적외 영상을 이용한 청계천 복원 전의 도시 지표 열 환경 특성 분석)

  • Jo Myung-Hee;Kim Hyung-Sub;Yu Seong-Ok;Kim Sung-Jae;Kim Yeon-Hee
    • Proceedings of the KSRS Conference
    • /
    • 2006.03a
    • /
    • pp.240-245
    • /
    • 2006
  • 오늘날 도시인구집중화 현상에 따른 대규모 도시개발과 도시역의 확대로 지표면의 피복 변화가 극심하게 이루어지고 있는 한편 이러한 현상으로 인해 도시의 내 외적 경관변화 뿐만 아니라 지형 및 기온상승, 바람장의 변화 등 복합적인 국지기후 변화를 초래하게 되었다. 본 연구에서는 이러한 도시의 기후 변화에 따라 청계천 복원 전의 도시 지표 열 환경 특성을 분석을 수행하고자 한다 도시지역의 열환경 분석을 위하여 기존에는 주로 Landsat TM/ETM+ 위성영상 자료를 사용하였으나 2003년 5월 위성 센서의 고장으로 위성영상 자료의 사용이 불가피하게 되었다. 이에 대체 방안으로 ASTER 영상 열적외 센서에서 취득한 지표온도 값과 현장에서 취득한 AWS자료와의 상관성 분석을 실시하였으며, 이를 기반으로 청계천 주변의 근접성 분석 및 토지이용별 지표온도 분포 패턴 등 도시 열 환경 변화 탐지 및 분석을 위하여 GIS 및 RS 분석을 실시하였다.

  • PDF

Determination of operating factor and characteristics of membrane fouling on hybrid coagulation pretreatment-UF system in drinking water treatment (정수처리 응집·한외여과 시스템의 연속운전을 통한 운전조건 결정 및 막오염 특성에 관한 연구)

  • Moon, Seong-Yong;Yun, Jong-Sub;Kim, Seung-Hyun
    • Journal of Korean Society of Water and Wastewater
    • /
    • v.22 no.2
    • /
    • pp.267-274
    • /
    • 2008
  • This study is about efficiency of pretreatment process and operating factor to membrane process at continuous coagulation/ultrafiltration process in water treatment. The capacity of pilot plant was $0.06{\beta}(C)/d$. The raw water used was from Nakdong stream which was characteristized by high organic matter and high turbidity. The result of the test was that coagulation is good process as to high removal rate to organic matter and turbidity but It caused problem to membrane pore blocking. This paper is to determine the membrane fouling potential under different membrane flux, backwash pressure and linear velocity. Backwash pressure and flux is important parameter on operation of membrane system. Those are directly affected on membrane system. When backwash pressure increased from 150 kPa to 200 kPa, the result showed that fouling (pressure increase rate) changed from 3.69 kPa/h to 0.93 kPa/h and the recovery rate changed from 90.7 % to 82.0 %. Linear velocity had slightly effect on fouling. Linear velocity increased from 0.2 m/s to 0.5 m/s, the corresponding pressure rate changed from 0.93 kPa/d to 0.77 kPa/d.

An Analysis on Water Pollution Degree by the Watershed considering Landcover Types in the Mid-Nakdong River (낙동강중류의 토지피복형태를 고려한 유역별 수질오염도 분석)

  • Lee, Woo-Sung;Jung, Sung-Gwan;Park, Kyung-Hun;You, Ju-Han
    • Journal of Environmental Science International
    • /
    • v.15 no.4
    • /
    • pp.349-357
    • /
    • 2006
  • The purpose of this study is to evaluate the water pollution degree in the Mid-Nakdong River watershed regarding to landcover types using GIS method. As a result of landcover classification, rate of urban appeared highly on Daegu Metropolitan city. Also, rate of agriculture showed highly in the riparian zones of the Nakdong and Guemho River and rate of forest appeared highly in the borders of the study area. To identify the groups of watershed with similar landcover patterns using the Cluster Analysis. According to the cluster analysis, the fifty sub-watersheds were grouped in three clusters, 'Urban watershed', 'Agriculture watershed', 'Forest watershed'. The proportion of urban area in each cluster had a positive correlation with water pollution degree. Otherwise, the proportion of agriculture in the Agriculture watershed had a high positive correlation with water pollution degree. Therefore, it is necessary to estimate environmental capacity of water duality considering ecological and environmental characteristics of watershed ecosystem and expand water duality monitoring systems to small stream.

MEASUREMENT OF FLOW DISTRIBUTION IN A STRAIGHT DUCT OF RAILWAY TUNNEL MOCK-UP USING PIV AND COMPARISON WITH NUMERICAL SIMULATION (PIV 기법을 이용한 모형철도터널 직관덕트에서 유동 분포 계측 및 수치해석 결과와의 비교분석)

  • Jang, Y.J.;Jung, W.S.;Park, I.S.
    • Journal of computational fluids engineering
    • /
    • v.15 no.3
    • /
    • pp.39-45
    • /
    • 2010
  • The turbulent flows in a tunnel mock-up($10L{\times}0.5W{\times}0.25H$ m3 : scale reduction 1/20) with rectangular cross section were investigated. The instantaneous velocity fields of Re = 49,029, 89,571 were measured by the 2-D PIV system which is consisted of double pulsed Nd:Yag laser and the tracer particles in the straight-duct mock-up where the flows were fully developed. The mean velocity profiles were taken from the ensemble averages of 1,000 instantaneous velocity fields. Simultaneously, numerical simulations(RANS) were performed to compare with experimental data using STREAM code. Non-linear eddy viscosity model (NLEVM : Abe-Jang-Leschziner Eddy Viscosity Model) was employed to resolve the turbulent flows in the duct. The calculated mean velocity profiles were well compared with PIV results. In the log-law profiles, the experimental data were in good agreement with numerical simulations all the way to the wake region except the viscous sub-layer (near wall region).

A Study on the Near Wake of a Square Cylinder Using Particle Image Velocimetry (III) - Phase Average - (PIV기법을 이용한정사각실린더의 근접후류에 관한 연구 (III) - 위상평균유동장 -)

  • Lee, Man-Bok;Kim, Gyeong-Cheon
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.25 no.11
    • /
    • pp.1527-1534
    • /
    • 2001
  • Phase averaged velocity fields in the near wake region behind a square cylinder have been (successfully) obtained using randomly sampled PIV data sets. The Reynolds number based on the flow velocity and the vertex height was 3,900. To identify the phase information, we examined the magnitude of circulation and the center of peak vorticity. The center of vorticity was estimated from lowpass filtered vorticity contours (LES decomposition) adopting a sub-pixel searching algirithm. Due to the sinusoidal nature of firculation which is closely related to the instantaneous vorticity, the location of peak voticity fits well with a sine curve of the circulation magnitude. Conditionally-averaged velocity fields represent the barman vortex shedding phenomenon very well within 5 degrees phase uncertainty. The oscillating nature of the separated shear layer and the separation bubble at the top surface are clearly observed. With the hot-wire measurements of Strouhal frequency, we found thats the convection velocity changes its magnitude very rapidly from 25 to 75 percent of the free stream velocity along the streamwise direction when the flow passes by the recirculation region.