• International Journal of Naval Architecture and Ocean Engineering
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• 제2권4호
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• pp.185-194
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• 2010

A pumpjet propulsor (PJP) was designed for an underwater body (UWB) with axi-symmetric configuration. Its performance was predicted through CFD study and models were manufactured. The propulsor design was evaluated for its propulsion characteristics through model tests conducted in a Wind Tunnel (WT). In the concluding part of the study, evaluation of the cavitation performance of the pumpjet was undertaken in a cavitation tunnel (CT). In order to assess the cavitation free operation speeds and depths of the body, cavitation tests of the PJP were carried out in behind condition to determine the inception cavitation numbers for rotor, stator and cowl. The model test results obtained were corrected for full scale Reynolds number and subsequently analyzed for cavitation inception speeds at different operating depths. From model tests it was also found that the cavitation inception of the rotor takes place on the tip face side at higher advance ratios and cavitation shifts towards the suction side as the RPS increases whereas the stator and cowl are free from cavitation.

• Journal of Advanced Marine Engineering and Technology
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• 제34권5호
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• pp.718-724
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• 2010

공동수조와 예인수조에서의 프로펠러 단독특성 차이를 보정할 수 있는 위벽효과 연구를 수행하였다. 우선 공동수조의 실험에서 프로펠러의 상류가 아닌 작동 평면 위치에서 계측된 유속을 프로펠러 전진속도로 정의할 경우, 위벽효과의 수정 량 및 단독특성차이가 현저히 줄어드는 것을 확인하였다. 다음으로 양력판 이론에 의한 단독특성 계산을 통해, 프로펠러 평면에서의 위벽효과를 구하고 앞의 결과에 추가적인 보정을 수행하였다. 그 결과, 예인수조에서의 단독특성과 더욱 더 좋은 일치를 보여 주는 것을 확인하였다.

• 대한조선학회논문집
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• 제53권6호
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• pp.465-472
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• 2016

A study was carried out to investigate typical features of natural supercavitation generated behind axisymmetric bodies such as disk and cone shaped cavitators. Main focuses of the study were to observe formation process of the supercavity and to measure drag forces acting on cavitators. Experiments were carried out at the cavitation tunnel of the Chungnam National University (CNU-CT), which has a capability to make sufficient flow speed for supercavitation experiments and to remove broken cavity bubbles coming back to the test section. Blockage effects on supercavity dimensions were evaluated and an effort was made to correlate tunnel experiments with unbounded flow. On the basis of experimental and numerical results, geometrical features of supercavities and characteristics of drag forces were examined and their relations were proposed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제4권2호
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• pp.123-131
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• 2012

When the object is traveling in the water at tremendously high speeds, the cavity forms and grows up at a fore part of the object called cavitator, and the object is eventually enveloped by vaporized water, supercavitation. As a result, the only part of the object in direct contact with the water is the cavitator, so skin-friction drag is significantly reduced. This is why recently supercavitating objects have been interested in many applicable fields. In this study we are focused out attention on supercavitating flows around various shapes of two and three dimensional cavitators. First, general features of supercavitation are examined by analyzing results obtained by the previously developed numerical method. Second, experimental observations are carried out at a cavitation tunnel at the Chungnam National University (CNU CT), and supercavity dimensions are scrutinized.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.443-449
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• 2010

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.

• 대한조선학회논문집
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• 제53권3호
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• pp.180-187
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• 2016

As distinct from a slender body, the separation of the boundary layer on a bluff body give rise to complex wakes in which various kinds of vortices form, develop and interact with each other. In this paper, we investigate cavitation wake field behind wedge shaped two-dimensional fin models. Eight different models are tested at the Chungnam National University Cavitation Tunnel (CNU-CT). First, we measure wake cavity shapes and compare with numerical results, which shows the good agreement with each other. In addition, we demonstrate that wake flow characteristics of the control fin are clearly identified by the correlation analysis of high-speed camera images and pressure fluctuation measurements.

• International Journal of Naval Architecture and Ocean Engineering
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• 제2권1호
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• pp.39-44
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• 2010

Recently underwater systems moving at high 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 cavtiator yielding a sufficiently large enough cavity to surround the body. Second, numerical predictions of supercavity are validated by comparing, with experimental observations carried out in a high speed cavitation tunnel at Chungnam National University (CNU CT).

• 한국해양공학회지
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• 제32권1호
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• pp.36-42
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• 2018

Unlike a slender body, vortices are shed off alternately in the wake of a blunt body. In the case of liquid flows, when the pressure falls below the vapor pressure, cavitation occurs in the vortex core and affects the formation of the vortex street. This phenomenon is of major importance in many practical cases because the alternate shedding of vortices creates imbalanced forces on the body. Hence, it is very important to determine the shedding frequency of cavitating vortices. In this paper, the unsteady cavitating flow around a two-dimensional wedge-shaped submerged body was simulated using the commercial code STAR-CCM+. A numerical investigation of the structure of cavitating vortices was performed for a model with an apex angle of $20^{\circ}C$. The results were validated by comparing them with experimental measurements carried out at a cavitation tunnel of Chungnam National University (CNU-CT). It was found that the shedding frequency of the vortex increased by up to 18%, which was strongly affected by the development of cavitation.