• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2150-2158
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• 1992

This study was carried out to investigate the flow structure and mixing process of a cross mixing flow formed by two round jets with respect to the ratio of mass flow rate. This flow configuration is of great practical relevance in a variety of combustion systems, and the flow behaviour of a cross jet defends critically on the ratio of mass flow rate and the cross angle. The mass flow rate ratios of two different jets were controlled as 1.0, 0.8, 0.6, and 0.4, and the crossing angle of two round jets was fixed at 45 degree. The velocities issuing from jet nozzle with an exit diameter of 20mm were adjusted to 40m/s, 32m/s, 24m/s, and 16m/s, and the measurements have been conducted in the streamwise range of $1.1X_0$to $2.5X_0$ by an on-line measurement system consisted of a constant temperature type two channel hot-wire anemometry connected to a computer analyzing system. The original air flow was generated by a subsonic wind tunnel with reliable stabilities and uniform flows in the test section. For the analysis of the cross mixing flow structure in the downstream region after the cross point, the mean velocity profiles, the resultant velocity contours, and the three-dimensional profiles depending upon the mass flow rate ratio have been concentrately studied.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.699-705
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• 2007

Recent experimental data shows that the noticeable feature of irregular roughened spots on the fuel surface occurs during the combustion test with PMMA/GOX in the hybrid rocket motor. The generation of these unexpected patterns is likely to be resulted from the disturbed boundary layer due caused by wall blowing which is intented to simulate the process of fuel vaporization. LES technique was implemented to investigate both the flow characteristics near fuel surface and the subsequent evolution of turbulence modified by the wall blowing. Simple channel geometry instead of circular grain configuration was used for the investigation without chemical reactions in order to allow for a focused examination on the near-wall behavior at the Reynolds number of 22,500. It was shown that the wall blowing pushed turbulent structures upwards making them tilted and this skewed displacement, in effect, left the foot prints of the structures on the surface. This change of kinematics may explain the formation of irregular isolated spots on the fuel surface observed in the experiment.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.2
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• pp.215-220
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• 1996

Seasonal and interannual variations of the oceanic condition in the surface layer of the northwestern East Sea are described. The seasonal variation shows two types in the water circulation. In the first type the East Korean Warm Current (EUC) Water are dominant in the East Korean Bay in spring, while in summer the cold water region develops as the North Korean Cold Current (NKCC) becomes strong. In the second type the cold water appears in the East Korean Bay from spring, but in summer the EKWC comes close to the coast, thus influencing the coastal cold water region. The characteristics of the interannual variation can be classified into 4 types according to the relative strength between the EKWC and the NKCC, and the paths of these currents. In each case various sizes of cyclonic cold eddies and/or anti-cyclonic warm eddies are formed frequently in the East Korean Bay.

• Solar Energy
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• v.13 no.1
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• pp.22-30
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• 1993

This Paper deals with the experimental study of the axisymmetric air jet impinging vertically on the flat heating surface with and without swirl. The purpose of this study is to investigate the characteristics of flow, augmentation of heat transfer rate, turbulent intensity, and the comparison of heat transfer rate, the optimal swirling condition about the swirl and nonswirl axisymmetric air jet. In order to augment the heat transfer on the flat heating surface without introducing any additional power, the technique used in the present work was placement of twisted tape inserted pipe in front of the nozzle exit in order to make a swirl. The effect of swirl degree is investigated in case of S=0., 0.056, 0.111, 0.222 and the velocity of the jet was 14, 20, 26, 32, 38, 44m/s. The distance between the nozle exit and the stagnation point on the impinging plate was the H/D=$1{\sim}14$. In order to analyze of the flow structure which increase heat transfer, the velocity and the turbulent intensity of the axisymmetric jet was measured by a hot wire anemometer according to the swirl number and H/D.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.169-169
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• 2015

유사 입자의 크기는 유사의 특성 및 그에 따른 거동 변화에 중요한 영향을 미친다. Stokes 침강 속도 모형에서 유사의 침강 속도에 가장 많은 영향을 주는 인자는 유사의 크기인 것 또한 확인된다. 유사 입자의 크기가 약 $60{\mu}m$보다 작은 유사들은 알갱이 사이의 점착력을 무시할 수 없다. 이로 인해 유사들은 응집 현상을 겪으며 입자 본래의 크기보다 크기가 큰 플럭을 형성하는 점착성 유사로 분류된다. 응집 현상이란, 흐름 내 점착성을 띠는 일차입자(Primary Particle)가 응집과 파괴를 반복하며 플럭을 형성하는 현상을 뜻한다. 입자 간의 충돌을 통해 응집이 진행되며 난류 전단으로 인해 형성된 플럭의 파괴가 발생한다. 많은 연구에서 점착성 유사의 충돌을 야기하는 가장 지배적인 원리는 난류라 알려져 있다. 이러한 응집 현상으로 인하여 플럭의 크기와 밀도는 지속적으로 변화를 겪으며 비점착성 유사와 다른 특징들을 보인다. 흐름에 존재하는 유사의 이동은 이송-확산 방정식을 통해 표현된다. 이송-확산 방정식은 시간 변화에 따른 농도의 변화를 입자의 침강과 난류 및 유사 자체의 특징에 의한 확산으로 해석한다. 침강속도로 대변되는 이송과 달리, 확산은 난류흐름 내에서 유사가 확산되는 정도를 정량화하기 위한 인자가 요구된다. 난류에 의한 유사의 확산은 유사 자체 특성에 따른 물질 확산에 비하여 매우 큰 값을 가지며, 이를 확산 계수로 개념화 한다. 확산계수는 와점성계수와 Schmidt 수(${\sigma}_c$)의 비로 정의된다. ${\sigma}_c$는 난류의 점성과 난류로 인한 부유과정에 의해 유사가 확산되는 정도를 나타낸다. 이에 따라 ${\sigma}_c$의 변화가 유사의 부유 및 침강거동에 많은 영향을 미칠 것이라 판단되나, 국내외에서 수행된 연구 동향에서는 ${\sigma}_c$를 0.5부터 1.0 사이의 상수를 적용하여 수행되었다. 이에 본 연구에서는 ${\sigma}_c$의 크기에 따라 달라지는 유사의 부유 및 침강 변화에 의한 총 부유량을 살펴보고자 한다. 유사의 점착성을 고려할 수 있는 1DV 수치 모형을 이용하여 비점착성 유사와 점착성 유사를 대상으로 수치연구를 수행하며, 유사의 크기 및 ${\sigma}_c$의 변화에 따른 총 부유량 경향을 살펴본다. 그 결과, 점착성 유사는 ${\sigma}_c$의 증가에 따라서 유사의 총 부유량이 증가하는 현상이 나타난 반면 비점착성 유사는 ${\sigma}_c$의 증가에 따라 유사의 총 부유량이 감소하는 경향이 나타났다. 그러나 크기가 아주 작은 비점착성 유사를 대상으로 수치 연구를 수행한 결과, ??에 따른 총 부유량의 경향은 유사의 점착성에서 기인하는 것이 아닌 입자의 크기로부터 야기되는 특성이라는 결론이 도출되었다.

• Journal of Power System Engineering
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• v.13 no.5
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• pp.34-39
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• 2009

In this paper, the CFD analysis using various turbulent models has been performed to evaluate which type of turbulent models can predict well the mixing flow structure of $45^{\circ}$ impinging round jet. This CFD analysis has been carried out through the commercial Fluent software. As a result, any of turbulent models cannot predict the experimental results definitely all over the flow range. However, as compared with the experimental results, the turbulent model of realizable(RLZ) k-$\varepsilon$ only predicts well in the limited range between X/$X_0=1.1$ and X/$X_0=2.0$.

• Animal Systematics, Evolution and Diversity
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• v.4 no.2
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• pp.121-136
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• 1988

본 연구는 1969년 12월부터 1987년 10월까지 제주도의10개 지역 (제주항, 우도, 성산포, 표선, 서귀포, 숲섬, 화순, 가파도, 비양도, 한림)에서 채집된 표본들을 동정·분류한 결과(9과 31종)와 이미 발표된 종을 종합하여 제주도 연안의 유영목을 정리하였다. 그 결과 모두 11과 31속 45종이었다. 이들 중 4종 (Lepidasthenia berkeleyae, Brania clavata, Sphaerosyllis hirsuta 및 Ceratonereis singularis)은 한국미기록종이며, 13종은 제주도 연안에서만 발견되었다. 한국미기록종에 관하여는 그림을 그리고 기재하였다. 45종 중 난온수형이 22종 (48.89%)으로 가장 많았고, 범세계형이 10종(22.22%), 열대수형이 8종(17.78%), 냉온수형이 4f종(8.89%), 냉수형이 1종(2.22%) 의 순으로 나타났다. 난온수형이 가장 많이 나타난 현상은, 제주도가 위치하고 있는 해형, 즉 쿠로시오 난류의 영향을 크게 받고 있다는 사실과 부합된다.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.2
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• pp.71-79
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• 1998

Fish larvae and environmental variables were collected in the sea around Cheju Island of Korea in November, 1986. Fish larvae were found at the 43 of 44 stations. Abundance of fish larvae rangεd from 3 to 259 indiv./$10^3\;m^3$ (average 50 indiv./$10^3\;m^3$) Dominant species were Engraulis japonicus, Champsodon snyderi, Gobiidae, Sebastiscus marmoratus, and Synagrops philippinensis, which comprised 56.6% of total fish larvae abundance. 43 stations were c1assified into two groups by c1uster analysis based on the abundance of fish taxa. Most stations of Group I were located in the middle reach of Tsushima Current and had higher number of species and abundance than the sites of Group II which cover the marginal areas of Tsushima Current, Korean Coastal Waters, and coastal water of China. The dominant taxa in the sites of the Group I were E. japonicus, Gobiidae, S. philippinensis, Aulops japonicus, Bregmaceros spp., Benthosema pterotum, Lampanctus spp., etc., all of which are typical warm-water species. Therefore, Tsushima Current seems to be the most critical factor regulating the structure of fish larvae community in the study area. The discriminant analysis using the environmenta1 variables (temperature, salinity, and dissolved oxygen) produced result with a difference only of 11.6% from that of c1uster analysis using the taxa composition and abundance data. Consequently, the structural type of fish larvae community can be used for predicting the changes of environmental conditions in the study area.

• Journal of the Korean Society of Safety
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• v.8 no.3
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• pp.19-25
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• 1993

This paper deals with the experimental study of the turbulent characteristics in the swirling coaxial Jets. In this research, the experimental study has been carried out to investigate the effects of swirl number and equivalence ratio on the flow characteristics in nonreacting flow field of the model combustor which symplifys the continuous type combustor for the practical use. Author particularly Intends to find out the fuel-air mixing In the recirculation zone In order to make sure the effects of swirl number and equivalence ratio on the stabilization of flame.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.10a
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• pp.311-312
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• 2001

동물플랑크톤처럼 미약한 유영능력을 갖고 있는 분류군의 종조성과 분포는 수온, 염분, 먹이 등과 같은 물리ㆍ생물학적인 환경요인 이외에 해수의 흐름에 크게 영향을 받는다. 그러므로, 부유생태계에서 동물플랑크톤에 의한 에너지 흐름을 명확히 구명하기 위해서는 각 구성 종들의 특징과 역할에 대한 자료의 축적이 무엇보다 중요하다. 본 연구에서는 쓰시마 난류의 영향을 직ㆍ간접적으로 받고 있는 가막만 남쪽 해역을 중심으로 하계에 출현하는 동물플랑크톤의 출현 양상과 역할을 살펴보고자 한다. (중략)