• Journal of Korea Water Resources Association
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• v.44 no.3
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• pp.189-198
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• 2011

The aim of this study is to compare k-$\varepsilon$ and k-$\omega$ closures under the condition of oscillatory layer flow at high Reynolds number. A one dimensional vertical model incorporated with flow momentum equations and turbulence models (k-$\varepsilon$ and k-$\omega$) is applied to the laboratory measurements in the turbulent oscillatory boundary layer. The numerical simulation reveals that both turbulence models calculate similar velocity profiles and turbulent kinetic energy (TKE). In addition, both deliver high accuracy under the condition of negligible spanwise pressure gradient. Therefore, it is recommended in this study to use k-$\varepsilon$ closure, of which numerical coefficients have been calibrated from many studies, for the cases of straight channel, estuary, and coastal environment where the spanwise pressure gradient is not significant.

• Journal of Power System Engineering
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• v.5 no.3
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• pp.31-37
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• 2001

A study to obtain the enhancement of turbulence at low Reynolds number is carried out by adding ultrasonic force into the jet flow field of a coaxial circular pipe which can afford the sufficient data of flow characteristics with the shear flow and turbulence flow in spite of its simple shape. A coaxial circular flow field is made vertically in a large and transparent acryl tank. The time mean velocity vector, distribution, kinetic energy and turbulence intensity formed in the complex flow field of turbulence enhancement are investigated, observed and discussed at Reynolds number of 2,000, 3,000 and 5,000 by using PIV measurement, in results, the validity of ultrasonic to obtain the enhancement of turbulence is certified.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.241-244
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• 2002

Large eddy simulation of a circular jet at the Reynolds number of 10000 is performed to investigate turbulence suppression effect with single frequency excitation at the non-dimensional frequency of 0.017. Instantaneous flow fields show that, with excitation, naturally occurring energetic vortices are suppressed through earlier saturation and breakdown of the shear layer vortices into fine grained turbulence. Due to the excitation, the Reynolds stresses are larger for the excited case near the jet and turbulence suppression begins afterward. The Reynolds normal stresses show largest suppression in the shear layer near the jet and in the centerline further downstream, while the Reynolds shear stress shows largest suppression in the shear layer at all the downstream locations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.115-118
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• 2004

In this study, amplitudes of turbulence excitation are obtained for selected tubes inside the KSNP SG and their normal work-rates are investigated to estimate the magnitude of fretting-wear. From the results of numerical calculation, row 40&41 tubes show the maximum work-rates. Up to this row number, the work-rates inside the row 41 have much larger values than those of outside tubes. This phenomenon reveals the particular central one which has larger normal work-rate than that of outside zone. It turns out that both of the higher local mode at the U-bend region and the larger value of effective mass in the central region Increase the normal work-rate enormously.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1400-1405
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• 2001

In this study, an analysis program to assess the susceptibility of steam generator tubes due to the flow-induced vibration was developed. Analysis of fluid-elastic instability and random turbulence excitation for the U-tube bundle in CE-type steam generator was accomplished. The effective mass distribution along the U-tube was obtained to calculate the natural frequency and dynamic mode shape. Finally, stability ratios and rms vibration amplitude for selected tubes are obtained.

• Proceedings of the EASDL Conference
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• 2003.09a
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• pp.24-36
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• 2003

본 연구에서는 국의 영양소 구성의 다양성을 평가하고 국의 영양에 대하여 고찰하고 영양소 구성을 평가하는 방법에 대하여 고찰하였다. 국의 조리법에 관한 전문서적, 전문잡지 등으로부터 562가지의 국의 레시피를 수집하고 168가지의 전형적인 국의 레시피를 만들어 이를 기본 데이터로 하여 국의 열량 및 영양소를 분석하였다. 결과는 다음과 같다. 1. 168가지 국의 열량 및 영양소 함유량의 평균치를 보면, 한국인을 위한 영양권장량에 대한 충족률이 6.3%(열량)～41.3%(비타민 A)의 범위에 이른다. 그리고 (밥과 국)만으로도 지방을 제외한 영양소를 한 끼 영양권장량의 50% 이상 섭취할 수 있다. 국은 영양이 풍부한 음식임이 분명하다. 2. 영양소 구성의 다양성을 평가하기 위하여 한 끼 영양권장량의 50% 이상 섭취할 수 있는 영양소의 구성을 살펴보았다. 영양소 구성의 다양성에 따르면 (밥과 국)의 82.8%가 '양호한 영양소 구성' 이상이라고 평가되었다. 국은 훌륭한 영양소 구성을 가진 음식으로 평가한다. 3. (밥과 국)의 영양소 구성의 다양성과 국을 만드는데 쓰이는 식재료의 수, 종류, 중량과의 관계를 분석한 결과로부터 '양호한 영양소 구성'을 가진 국을 만드는 간단한 지침을 얻었다. 실제로 국을 만들 때 주로 쓰이는 식재료인 담색채소, 녹황색채소, 어패류, 육류, 두류ㆍ두제품 중에서 3가지를 100g 이상 되도록 준비하여 국을 만들면 '양호한 영양소 구성'을 가진 국을 만들 수 있다. 4. (밥과 국)의 영양소 구성의 다양성의 특징을 바탕으로 적절한 영양을 섭취할 수 있는 식사가 되기 위해 다른 반찬을 곁들이는 지침을 제안하였다. 국을 만들 때 1～2가지의 식재료를 이용한다면 영양소 구성의 다양성이 모자라기 쉽기 때문에 육류ㆍ어패류ㆍ난류 두류 반찬과 채소 반찬을 반드시 갖추어야 한다. 반면, 국의 식재료가 6이상이면 열량과 지방이 넘칠 수 있으므로 육류ㆍ어패류ㆍ난류ㆍ두류 반찬을 반드시 갖출 필요가 없다.

• Fire Science and Engineering
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• v.18 no.2
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• pp.34-40
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• 2004

The effects of external flow excitation with various frequencies and amplitudes on the flame behavior and pollution emission characteristics from a laminar jet flame are experimentally investigated. Measurements of $NO_x$ emission indices ($EINO_x$), performed in vertical lifted flame like turbulent with various exciting amplitude at a constant resonance frequency, have been conducted. It was also conducted to investigate the effects of excited frequency at a constant exciting amplitude on $NO_x$ emissions with a various frequency ranged 0 Hz to 2 KHz. From the vertical lifted turbulent flame of the excited jet with resonance frequency by strong excitation was shown that the dependence of $NO_x$ emission could be categorized into three groups Group I of long flame length with high disturbances yielding high $NO_x$ emission, Group II of intermediate flame length and relative narrow flame volume with low disturbance yielding low $NO_x$ emission and Group III of long flame length and large flame volume with high time ＆ space disturbances behaviour yielding high $NO_x$ emission.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.217-228
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• 2009

Sections under the influence of merging in an uninterrupted facility create irregular interaction between vehicles, such as lane change, speed acceleration and deceleration because of the merging of ramp traffic flows which have traffic characteristics different from those of the main line. This causes a confused traffic flow phenomenon(turbulence), which is considered an unstable traffic characteristic between various continuous points in consideration of v conditions. In this study, in merge influence sections, detectors by lane-point were installed to create time and space-series -traffic data. The least significant difference(LSD), as the criteria for discriminating a significant speed change between points, was calculated to examine the turbulence. As a result, turbulence in merge influence section was found to change the zones of such occurrence and the seriousness levels according to traffic condition. Thus, the maximum merge influence section due to the turbulence was created in the traffic condition before congestion when traffic increases. According to characteristics of changes in speed, merge influence section was divided into upstream 100m$\sim$downstream 100m(a section of speed reduction), and downstream 100m$\sim$downstream 400m(a section of reduced speed maintenance and acceleration).

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.293-300
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• 2007

Turbulent boundary layer over an underwater vehicle is formed when it moves underwater and wall pressure fluctuation within the turbulent boundary layer generates flow-induced noise by exciting the elastic hull of the underwater vehicle. One of the methods to reduce this flow noise is to attach a compliant layer on the surface of the vehicle. In order to observe the possibility of noise reduction in the water when the compliant layer treatments are applied on the surface, three types of specimens those are a bare steel plate, a steel plate coated with neoprene and a steel plate with polyurethane coating material are tested at various flow speeds in a low noise cavitation tunnel. This paper presents the results of measurements and analysis of wall pressure fluctuations which is a main source of flow noise, within the turbulent boundary layer on three specimens. Its results could be shown that about 10dB reduction of wall fluctuation pressure at high frequencies was achieved due to the dissipation of turbulent energy by the compliant coating while it makes the turbulent boundary layer thicker and changes the behavior of turbulent flow in the layer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.1
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• pp.31-40
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• 2004

Direct numerical simulations were performed to analyze the effects of time-periodical blowing through a spanwise slot on a turbulent boundary layer. The blowing velocity was varied in a cyclic manner from 0 to 2A$^{+}$(A$^{+}$ =0.25, 0.50 and 1.00) at a fixed blowing frequency of f$^{+}$=0.017. The effect of steady blowing (SB) was also examined, and the SB results were compared with those for periodic blowing (PB). PB reduced the skin friction near the slot, although to a slightly lesser extent than SB. PB was found to generate a spanwise vortical structure in the downstream of the slot. This vortex generates a reverse flow near the wall, thereby reducing the wall shear stress. The wall-normal and spanwise turbulence intensities under PB are increased as compared to those under SB, whereas the streamwise turbulent intensity under PB is weaker than that under SB. PB enhances more energy redistribution than SB. The periodic response of the streamwise turbulence intensity to PB is propagated to a lesser extent than that of the other components of the turbulence intensities and the Reynolds shear stress.