• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.967-976
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• 1994

A tensor invariant model equation for the turbulent energy dissipation rate is proposed in the present study, which is able to simulate secondary straining effects such as curvature effects without the introduction of additional empirical input. The source term in this model has a combined form of the generation term due to the mean vorticity with the conventional one due to the mean strain rate. An extended low-Reynolds-number $k-\epsilon$ turbulence model involving this new model equation is tested for a turbulent Coutte flow between coaxial cylinders with inner cylinder rotated, which is a well defined example of curved flows. The predicted results indicate that the present model works much better for this flow, compared with previous models.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.65-69
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• 2015

하천에서 유사이동은 하천환경과 하천형상을 결정하는 주요 요소이므로 이를 해석하는 것은 매우 중요하다. 그러나 유사이동은 일반적으로 이상흐름 (two-phase flow)이며 난류를 동반하기에 이를 해석하기에는 쉽지 않다. 이상흐름을 해석하는 방법으로는 유사를 연속상인 유사구름(sediment cloud)으로 표현하여 해석하는 Euler-Euler 모형이 있으며 입자를 직접 추적하여 해석하는 Euler-Lagrange 모형이 있다. 본 연구에서는 유사이동 해석을 위하여 Euler-Lagrange 모형을 사용하였으며 흐름의 진동성분을 고려하기 위하여 EIM (Eddy Interaction Model)을 사용하였다. 유체의 유속은 Dou (1987)가 제시한 경험식을 사용하였고 난류운동에너지와 소산률은 Nezu and Nakagawa (1993)가 제시한 식을 사용하였다. EIM에서 입자에 발생하는 와의 영향시간(eddy interaction time)을 계산하기 위해 Gosman and Ioannides (1983)가 제시한 eddy lifetime과 eddy crossing time을 사용하였다. 유사입자는 입자의 운동량방정식을 풀어 그 거동을 추적하였으며 일정 시간 후 입자의 수를 이용하여 농도를 계산하였다. 유체에 발생하는 유속의 진동성분에 의해 입자가 부상하고 중력에 의해 흐름에 따른 일정한 농도분포 형태를 가지는 것을 확인하였다. 유사의 입자크기와 흐름에 따른 농도분포를 계산하였으며, 이를 측정치와 비교하여 EIM의 적용성을 확인하였다.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.32 no.3
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• pp.114-123
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• 2024

Recently, urban population congestion has caused significant traffic and air pollution problems in city centers. To address these issues, Urban Air Mobility (UAM) has been proposed, with commercialization targeted for 2025 in Korea. The Korea Meteorological Administration (KMA) has been conducting the K-UAM Grand Challenge in Goheung since 2022 to develop operational standards and relevant technologies. This study uses a ultrasonic anemometer at a height of 10 meters to analyze turbulence around the vertiport. Data was collected from November 2022 to November 2023. For turbulence analysis, the Eddy Dissipation Rate (EDR = ε^1/3), defined by the International Civil Aviation Organization (ICAO), was used. EDR was calculated using Kolmogorov's theory and derived from the energy spectrum. EDR values were classified into None, Light, Moderate, and Severe, and analyzed by season, day, and wind direction. The results showed strong daytime turbulence in summer, especially with southerly winds in spring and summer, due to sea breeze fronts. This study provides essential data for planning safe UAM operations considering weather conditions.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.31 no.3
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• pp.30-41
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• 2023

Aviation turbulence, caused by atmospheric eddies, is a disruptive phenomenon that leads to abrupt aircraft movements during flight. To minimize the damages caused by such aviation turbulence, the Aviation Meteorological Office provides turbulence information through the Korea aviation Turbulence Guidance (KTG) and the Global-Korean aviation Turbulence Guidance (GKTG). In this study, we evaluated the performance of the KTG and GKTG models by comparing the in-situ EDR observation data and the generated aviation turbulence prediction data collected from the mid-level Korean Peninsula region from January 2019 to December 2021. Through objective validation, we confirmed the level of prediction performance and proposed improvement measures based on it. As a result of the improvements, the KTG model showed minimal difference in performance before and after the changes, while the GKTG model exhibited an increase of TSS after the improvements.