• Title/Summary/Keyword: near stream

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The Effect of Free Stream Turbulence on the Coherent Structures in the near Wake of a Circular Cylinder (원주 후류의 응집구조에 대한 자유흐름 난류강도의 영향)

  • 정양범;양종필
    • Journal of Advanced Marine Engineering and Technology
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    • v.18 no.1
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    • pp.60-72
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    • 1994
  • The effect of free stream tubulence on the coherent structure in the near wake of a circular cylinder was investigated by a conditional sampling technique. The measurements were made from C.T.A. with hot wire I-probe and a Split-film sensor. Contours of phase-averaged velocity and vorticities were presented and discussed. It was found that the value of the vortex strength increased with increasing free stream turbulence which can enhance the roll-up of the shear layer.

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Present Status and Future Improvements in Groundwater Use Near Streams in the Anseongcheon watershed, Korea (하천 인근 지하수 이용 현황 및 관리 개선방향에 관한 연구)

  • Chung, Il-Moon;Hong, Sung Hun;Lee, Jeongwoo;Kim, Min Gyu
    • The Journal of Engineering Geology
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    • v.27 no.4
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    • pp.383-392
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    • 2017
  • Excessive abstraction of groundwater near streams for agricultural, domestic, or industrial use can significantly reduce the streamflow. Therefore, proper management of water resources must involve careful monitoring of groundwater use near streams. This study investigates the current status of groundwater intake plans in the Anseongcheon watershed, Korea, in order to understand the portion of groundwater wells according to distance from the stream and the distribution of wells near the stream. Among all the wells in the watershed, 20.5% were permitted and 31.3% were declared within 300m from the stream. In particular, among the wells located near streams, 11.4% were permitted and 88.6% were declared among the wells near streams. Therefore, the total amount of groundwater pumping rates from the declared wells is much higher than that from the permitted wells near the stream. Under current guidelines, investigations of the impact of groundwater use near a stream on streamflow depletion should only consider wells permitted by groundwater law. However, prudent management should also pay attention to declared wells, given their large number.

The effect of free stream turbulence on the near wake behind a circualr cylinder (원주의 근접후류에 대한 자유흐름 난류강도의 영향)

  • 김경천;정양범
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.6
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    • pp.2062-2072
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    • 1991
  • The effect of free stream turbulence on the flow characteristics behind a circular cylinder is investigated in the present experimental study. The various free stream turbulent intensities are generated by different combinations of cylinder locations and grid shapes. Split film sensor with constant temperature anemometer is used to measure the local instantaneous velocity components. Experimental results demonstrate the large scale coherent structures are rapidly distorted and the Strouhal number is decreased with increasing free stream turbulent intensity.

Effect of Nozzle Geometry on the Near Field Structure of Under Expanded, Dual, Coaxial Jet (노즐 형상이 부족팽창 동축제트 근접 유동장에 미치는 영향)

  • Lee, Kwon-Hee;Toshiake, Setoguchi;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1649-1654
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    • 2004
  • The near field structures of an under-expanded, dual, coaxial, jets issuing from the coaxial nozzles with four different geometries are visualized by using a shadowgraph optical method. Experiments are conducted to investigate the effects of the nozzle-lip thickness, secondary stream thickness, the nozzle pressure ratio and the secondary swirl stream on the characteristics of under-expanded jets. The results show that the presence of secondary annular swirling stream causes the Mach disk to move further downstream and increases its diameter, which decreases with a decrease in the nozzle-lip thickness. The secondary stream thickness has an influence on the location of an annular shock wave.

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Effects of Combustor-Level High Inlet Turbulence on the Endwall Flow and Heat/Mass Transfer of a High-Turning Turbine Rotor Cascade

  • Lee, Sang-Woo;Jun, Sang-Bae;Park, Byung-Kyu;Lee, Joon-Sik
    • Journal of Mechanical Science and Technology
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    • v.18 no.8
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    • pp.1435-1450
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    • 2004
  • Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The end wall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the end wall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the end wall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. In this study, the end wall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.

Fractal Dimension of Stream Networks and Main Stream Length with Map Scale (지형도(地形圖) 축척(縮尺)에 따르는 하천 수로망(水路網)과 본류(本流) 하천길이에 관한 Fractal Dimension)

  • Jeon, Min Woo;Cho, Won Cheol
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.12 no.4_1
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    • pp.97-106
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    • 1992
  • Total length of stream networks and main stream length vary with topographic map scales, and the stream length of drainage basin on topographic map can be viewed as a fractal. Total length of stream network and main stream length are represented as only stream area ratio($R_a$) based on Horton's laws, thereafter the fractal dimensions of stream network and main stream length are derived as a simple function of stream length($R_L$) and stream area ratios($R_a$) respectively. The derived equations of fractal dimension are applied to Sansung basin in Kum River and compared with the equations already existed. The stream network appeared as space filling with fractal dimension near 2 as map scale increases, while main stream length shows near 1. The results of this study are expected to be helpful in the quantitative analysis of drainage network composition with map scale.

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Development of Relational Formula between Groundwater Pumping Rate and Streamflow Depletion (지하수 양수량과 하천수 감소량간 상관관계식 개발)

  • Kim, Nam Won;Lee, Jeongwoo;Lee, Jung Eun;Won, You Seung
    • Journal of Korea Water Resources Association
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    • v.45 no.12
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    • pp.1243-1258
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    • 2012
  • The objective of this study is to develop the relational formula to estimate the streamflow depletion due to groundwater pumping near stream, which has been statistically derived by using the simulated data. The integrated surface water and groundwater model, SWAT-MODFLOW was applied to the Sinduncheon and Juksancheon watersheds to obtain the streamflow depletion data under various pumping conditions. Through the multiple regression analyses for the simulated streamflow depletion data, the relational formula between the streamflow depletion rate and various factors such as pumping rate, distance between well and stream, hydraulic properties in/near stream, amount of rainfall was obtained. The derived relational formula is easy to apply for assessing the effects of groundwater pumping on near stream, and is expected to be a tool for estimate the streamflow contribution to the pumped water.

An Influence of Livestock Farm's Wastewater on the Water Quality of Near Streams flowing into the Chungju Lake (축산농가 오수가 충주호에 유입되는 지천의 수질에 미치는 영향)

  • Oh, I. H.;Lee, J. H.;Hwang, H. S.;Jang, Y. S.
    • Journal of Animal Environmental Science
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    • v.11 no.2
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    • pp.89-96
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    • 2005
  • To investigate the influence of livestock farm's wastewater on the near stream, the water quality of 3 different streams are analysed after seasons. In summer, the minimum T-N in the upper stream was 0.005 ppm and the maximum T-N in the down stream was 5.005 ppm. The phosphate was detected only in down stream of S2 point and was 0.5 ppm. COD was varied from 8 ppm in upper stream to 20 ppm in down stream. In fall, the T-N and the phosphate had shown similar results as that of in summer, however COD was varied from 3 ppm in upper stream to 6 ppm in down stream. In winter, the minimum T-N in the upper stream was 0.053 ppm and the maximum T-N in the down stream was 0.51 ppm. The phosphate was detected only in down stream of S2 point and was 0.5 ppm. COD was varied from 3 ppm in upper stream to 6 ppm in down stream. To be becoming fall and winter, the water quality of streams showed better than that of summer, and the wastewater from the livestock farms had little influence on the near streams.

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Spatial Assessment of Effects of Near-Stream Groundwater Pumping on Streamflow Depletion (하천변 지하수 양수로 인한 하천수 감소 영향의 공간적 평가 - 죽산천 유역을 중심으로 -)

  • Lee, Jeongwoo;Kim, Nam Won;Chung, Il Moon;Lee, Min Ho
    • Journal of Korea Water Resources Association
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    • v.48 no.7
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    • pp.545-552
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    • 2015
  • The objective of this study is to spatially assess the streamflow depletion due to groundwater pumping near the main stream of Juksanchoen watershed. The surface water and groundwater integrated model, SWAT-MODFLOW, in this study, was used to simulate streamflow responses to each groundwater pumping from wells located within 500m from the stream. The simulated results showed that the streamflow depletion rate divided by the pumping rate for each well location ranges from 20% to 96%. In particular, the streamflow depletion exceeds 60% of pumping rate if the distance between stream and well is lower than 100 m, hydraulic diffusivity is higher than $500m^2/d$, and streambed hydraulic conductance is above 25m/d. The simulated results were also presented in the form of spatial distribution maps that indicate the fraction of the well pumping rate in order to show the effect of a single well more comprehensively and easily. From the developed areal distribution of stream depletion, higher and more rapid responses to pumping occur near middle-downstream reach, and the spatially averaged percent depletion is about 66.7% for five years of pumping. The streamflow depletion map can provide objective information for the near-stream groundwater permission and management.

Assessment of Degree of Naturalness of Vegetation on the Riverine Wetland (하천습지의 식생학적 자연도 평가)

  • Chun, Seung-Hoon
    • Journal of Environmental Impact Assessment
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    • v.20 no.1
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    • pp.1-11
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    • 2011
  • This study was carried out to suggest the baseline data necessary for vegetation restoration at riverine wetland within stream corridor. We used the prevalence index for wetland assessment by applying the method of weighted averages with index values based on five hydrophyte indicator status as defined by estimated probability occurred in wetland. We selected near nature and urbanized reach of Gap and Yanghwa streams as experimental site. Although two sites have some different disturbance and characteristics of watershed, they showed that similarity of vegetation community including three dominant species - Salix koreensis, Phragmites communis, Miscanthus sacchariflorus - was very high. But in case of Yanghwa stream, various kinds of emergent plants along wetted condition were distinctly occurred, resulted from difference of hydrological regime and substrate, etc. Degree of naturalness of vegetation at the sampled areas indicated that near nature area of Gap stream and all area of Yanghwa stream were fitted as riverine wetland, while urbanized area of Gap stream has changed into upland condition. In conclusion assessment system using prevalence index would be considered an effective method for evaluating of natural states of riverine wetland, but further integrated consideration of physical, hydrological, and biological factors of stream process, and also with considering the difference between those qualitative data of vegetation community.