• 대한조선학회논문집
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• 제37권1호
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• pp.10-25
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• 2000

모형 프로펠러 날개의 레이놀즈 수와 날개 앞날 표면거칠기 그리고 터널용수의 공기함유량이 모형 프로펠러의 캐비테이션 초기 발생, 캐비테이션 발생량 및 변동압력에 미치는 영향을 캐비테이션 터널에서 실험적으로 조사하였다. 'Sydney Express' 컨테이너선의 모형 프로펠러 캐비테이션 관찰과 변동압력 계측결과를 타 연구기관의 모형실험 결과와 실선 프로펠러의 캐비테이션 관찰 및 변동압력 계측치와 함께 비교하였다. 그 결과 매우 타당한 결과를 보여주었다.

• Ocean Systems Engineering
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• 제5권2호
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• pp.125-138
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• 2015

In this study, hydrodynamic performance of a 400 mm diameter horizontal axis marine current turbine model was tested in a cavitation tunnel with 1.21 m x 0.8 m cross-section for over a range of tip speed ratios. Torque and thrust data, as well as cavitation visualizations, for certain operating conditions were acquired. Experimental results indicated that the turbine can be exposed to significant amount of sheet and cloud cavitation over the blades along with vortex cavitation at the blade tips. Inception and distribution of cavitation along the blades of the model turbine were then modelled numerically for design operating conditions using a vortex lattice method. The method was also applied to a turbine tested previously and obtained results were compared with the data available. The comparison between simulation results and experimental data showed a slight difference in terms of span-wise extent of the cavitation region. The cloud and tip vortex cavity observed in experiments cannot be modelled due to the fact that the VLM lacks the ability to predict such types of cavitation. Notwithstanding, the use of such prediction methods can provide a reasonably accurate approach to estimate, therefore take the hydrodynamic effects of cavitation into account in design and analysis of marine current turbines.

• 대한조선학회논문집
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• 제47권2호
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• pp.122-131
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• 2010

The increasing size and speed of cargo ships result in high speed flow in propeller slipstream, and thereby cavitation is frequently observed on and around a rudder system. Rudder gap cavitation is the most difficult one to control and suppress among various types of the cavitation on a rudder system. In the present study, experiments of the incipient cavitation and pressure measurement were carried out for typical cargo ship rudder sections with and without the suppression devices, which were suggested by the authors. Fundamental understanding of the rudder gap cavitation inception was obtained along with its relevance to the surface pressure distribution. It is confirmed that the gap flow blocking devices effectively suppress the rudder gap cavitation and, at the same time, augment lift.

• 한국군사과학기술학회지
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• 제20권4호
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• pp.505-513
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• 2017

Cavitation is a phenomenon caused by vapour cavities that is produced in rapid pressure changes. When the cavitation happened, the sound pressure level of a underwater radiated noise is increased rapidly. As a result, it can increase the probability of the identification or classification of a our warship's acoustic signature by an enemy ship. However, there is a problem that it is hard to precisely detect the occurrence of a cavitation noise. Therefore, this paper presents recent improvements in terms of the cavitation noise measurement by using continuous wavelet transform and DEMON(Detection of Envelope Modulation on Noise) signal processing. Then, we present that the suggested scheme is more suitable for detecting the cavitation than existing algorithms.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1371-1379
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• 1997

The high pressure drop is frequently required in the by-pass line of the pump or of the heat exchanger in power plants. However, cavitation produced by a high pressure drop could damage the pipe and pump blades. Conical orifices are adopted to reduce cavitation due to high pressure drop. The discharge coefficients of conical orifice plates were measured by weighing method in the standard water flow system. The discharge coefficients were larger when the ratios of thickness of orifice edge to throat diameter were larger. The noise generated from a conical orifice due to cavitation was measured with a sound level meter and a hydrophone. With increasing the bore diameter of the orifice, the sound pressure level or the noise level due to cavitation became higher. The noise level was suddenly increased at the inception of cavitation.

• 대한조선학회논문집
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• 제37권4호
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• pp.40-47
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• 2000

수중익의 캐비테이션 소음이 캐비테이션 터널에서 측정되었다. 캐비테이션이 초기 발생하면 소음수준이 급격히 증가되며, 기포간에 상호간섭이 나타나지 않는 캐비테이션 수까지 증가된다. 그러나 케비테이션 수가 더욱 감소하여 기포간에 상호간섭이 나타나면, 오히려 소음수준이 감소되는 것으로 나타났다. 기포의 궤적과 체적의 변화는 각각 Lagrangian 추적법 및 Kirkwood-Bethe 가정하에 모형화된 방정식을 사용하여 해석하였다. 기포 체적변화의 수치계산 결과는 실험 결과와 비교적 일치되는 것으로 나타났다.

• 대한조선학회논문집
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• 제31권1호
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• pp.84-93
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• 1994

본 연구에서는 NACA0012단면을 갖는 타원형날개끝 캐비테이션과 유기소음특성에 미치는 표면거칠기의 영향이 실험적으로 조사되었다. 사용한 표면거칠기는 조도 $200{\mu}m$의 입자로서, 날개끝 3cm 구간에 부착하였다. 또한 날개끝과 앞날에 각각 3cm의 거칠기를 준 경우도 별도로 조사되었다. 캐비테이션 발생시험 결과 캐비테이션 초기발생위치는 실험한 받음각 범위에서 날개끝으로부터 대략 1/2 코오드정도 후류이며, 캐비테이션 수가 감소함에 따라 변화하는 형상을 보였다. 날개끝 캐비테이션에 의한 소음은 주파수 3-50kHs사이의 비교적 고주파수에서 음압이 증가하는 양상을 보였으나, 더 낮은 캐비테이션수에서 날개 앞날 캐비테이션으로 확장되면 전 주파수 범위에 걸쳐서 소음이 증가하었다. 캐비테이션과 소음발생은 표면거칠기가 증가할때 개선되는 경향을 보였으나 그 차이는 크지않았다. 날개 앞날과 끝날에 거칠기를 준 경우가 낮은 캐비테이션수에서 다소 유리한 캐비테이션 특성을 보여준 반면 양력-항력비의 감소에 따른 문제점도 지적되었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.413-418
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• 2008

Flow instability in the rocket turbo pump system can be caused by various reasons such as valve, orifice and venturi, etc. The inception of cavitation, especially in the propellant feeding system, is the primary cause of the mass flow and pressure oscillation due to cyclic formation and depletion of cavitation. Meanwhile, the main propellant in liquid rocket engine is the cryogenic one, which is very sensitive to temperature variation, and the variation of propellant properties caused by thermodynamic effect should be accounted for in the flow analysis. The present study focuses on the formation of cryogenic cavitations by adopting IDM model suggested by Shyy and coworkers. Also, the flow instability was investigated in the downstream of orifice by using a developed numerical code. Calculation results show that cryogenic cavitations can lead to flow instability resulting in mass flow fluctuations due to pressure oscillations. And the prediction of cavitations in cryogenic fluid is of vital importance in designing feeding system of LRE.

• Journal of Ship and Ocean Technology
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• 제1권2호
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• pp.19-30
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• 1997

The accurate prediction of the flow and the pressure distribution near the tip of the blade is crucial in determining the tip vortex cavitation inception which usually occurs on the blade tip or inside the core of the tip vortex just downstream of the blade tip. An improved boundary element method is applied to the prediction of the flow around propeller blades, with emphasis at the tip region. In the method, the Blow adapted grid and a higher order panel method, which combines a hyperboloidal panel geometry with a hi-quadratic dipole distribution, are used in order to accurately model the trailing wake geometry and the highly rolled-up regions in the wake. The method is applied to several propeller geometries and the results have been found to agree well to the existing experimental data. Inviscid flow methods are able to predict the pressures at the tip as well as the shape of the trailing wake. On the other hand, they are unable to determine the flow inside the viscous core of the tip vortex, where cavitation inception often occurs. Thus, a method is presented that treats the flow inside the viscous core. The inner flow is treated with a 2-D Clavier-stokes solution without making any assumptions for axisymmetric flow and conicity of the flow along the tip trajectory. The method can thus allow the treatment of general propeller blade configurations. The velocity and pressure distributions inside the core are shown and compared to those from other numerical methods.

• 대한조선학회논문집
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• 제41권6호
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• pp.15-23
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• 2004

In order to investigate efficiency and flowfield charateristics of the intake-diffuser for the ship waterjet propulsion, new experimental verification technology was set up in the cavitation tunnel. 1-hole and 5-hole pilot tubes were designed and manufactured to measure the pressure and velocity distributions at intake-diffuser entrance and impeller inlet. The calibration of the 5-hole pilot tubes is conducted at the cavitation tunnel The cavitation inception occurs at the intake lip, and the occurrence position depends on IVR (Inlet Velocity Ratio) condition. The present experimental device will be applied sufficiently for the development of the design and performance improvement technologies.