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A Study on Turbulent Wall Pressure Fluctuations Using a Coherent Structure Model
안병권(Ahn, Byoung-Kwon) 한국소음진동공학회 2007 한국소음진동공학회 논문집 Vol.17 No.5
In recent years, experimental and theoretical studies show that turbulent flows looking disordered have a definite structure produced repetitively with visible order. As a core structure of turbulence, hairpin vertices are believed to play a major role in developing and sustaining the turbulence process in the near wall region of turbulent boundary layers and may be regarded as the simplest conceptual model that can account for the essential features of the wall pressure fluctuations. In this work, fully developed typical hairpin vortices are focused and the associated surface pressure distributions and their corresponding spectra are estimated. On the basis of the attached eddy model, the overall surface pressure spectra are represented in terms of the eddy size distribution. The model is validated by comparison of predicted wavenumber spectra with existing empirical models, the results of direct numerical simulation (DNS) and also spatial correlations with experimental measurements.
안병권,정소원,김지혜,정영래,김선범,Ahn, Byoung-Kwon,Jung, So-Won,Kim, Ji-Hye,Jung, Young-Rae,Kim, Sun-Bum 한국군사과학기술학회 2015 한국군사과학기술학회지 Vol.18 No.3
Recently supercavitating underwater torpedo moving at high speed (over 200 knots) has been interested for their practical advantage of the dramatic drag reduction. Cavitator located in front of the torpedo plays an important role to generate a natural supercavity and control the motion of the object. Supercavity can be created artificially by injection of compressed gas from the rear of the cavitator at a relatively low speed. In this paper, we investigated physical characteristics of artificial supercavities through cavitation tunnel experiments. One of the main focuses of the study was to measure pressure inside the cavity, and examined variation of the gravity effects appearing according to different amount of injected air. It was also found that a stable supercavity could be sustained at injection rates less than that required to form the stable supercavity because of hysteresis effect.
점성 및 비점성 해석법을 이용한 초월공동 유동 수치해석
안병권,김지혜,최정규,김형태,나영인,이도형,Ahn, Byoung-Kwon,Kim, Ji-Hye,Choi, Jung-Kyu,Kim, Hyoung-Tae,Nah, Young-In,Lee, Do-Hyung 한국군사과학기술학회 2014 한국군사과학기술학회지 Vol.17 No.1
Recently supercavitating torpedo has been studied because of its high-speed performance as the next generation of underwater weapon systems. In this study, we present a numerical method based on the potential flow. Characteristic features of the shape of supercavities and drag forces are investigated. In addition, we introduce a viscous-potential method to compensate for the effects of viscosity. The results are compared with viscous calculations using a commercial package, FLUENT V13.
안병권(Byoung-Kwon Ahn),이창섭(Chang-Sup Lee),김형태(Hyoung-Tae Kim) 한국추진공학회 2010 한국추진공학회 학술대회논문집 Vol.2010 No.5
최근 초월공동 어뢰와 같이 극초고속으로 이동하는 수중운동체의 저항감소기법에 대한 연구들이 진행되고 있다. 본 연구에서는 수중 운동체 주위의 초월공동 동을 해석할 수 있는 수치기법을 개발하고, 다양한 형상을 가지는 축대칭 운동체에서 발생되는 초월공동을 추정하였다. 또한 충남대학교 캐비테이션터널에서 실험을 수행하여 발생되는 초월공동을 관찰하고 개발된 수치기법의 결과와 비교, 검증하였다. Recently underwater systems moving at hyper-speed such as a super-cavitating torpedo have been studied for their practical advantage of the dramatic drag reduction. In this study we are focusing our attention on super-cavitating flows around axisymmetric cavitators. A numerical method based on inviscid flow is developed and the results for several shapes of the cavitator are presented. First using a potential based boundary element method, we find the shape of the cavitator yielding a sufficiently large enough cavity to surround the body. Second, numerical predictions of super-cavity are validated by comparing with experimental observations carried out in a high speed cavitation tunnel at Chungnam National University (CNU CT).