• Title/Summary/Keyword: Cavitation characteristics

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Recent Topics on Cavitation Research

  • Kato Hiroharu
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.1-4
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    • 2002
  • This article presents the unique characteristics of cavitation, those are very high pressure and very high temperature even in a very short time. Such the high-pressure causes the destruction of material, which sometimes brings a severe problem to fluid machinery. However, if we look the cavitation from the different direction, such the high pressure can be used to various applications. The author presents two examples of the utilization of cavitation recently done at the Toyo University. Those are 'dispersion of spilled oil' and 'killing planktons'.

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Effect of cavitation on surface damage of 16.7Cr-10Ni-2Mo stainless steel in marine environment (해양 환경 하에서 16.7Cr-10Ni-2Mo 스테인리스강의 표면 손상에 미치는 캐비테이션의 영향)

  • Chong, Sang-Ok;Han, Min-Su;Kim, Seong-Jong
    • Corrosion Science and Technology
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    • v.14 no.5
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    • pp.239-246
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    • 2015
  • Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability, but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment. After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of $30{\mu}m$ and seawater temperature of $25^{\circ}C$, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation.

Characteristics of Cavitation Noise of 2-D Hydrofoils (2차원 날개단면들의 캐비테이션 소음 특성)

  • J.W. Ahn;I.H. Song;K.S. Kim;K.Y. Kim;I.S. Moon
    • Journal of the Society of Naval Architects of Korea
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    • v.37 no.2
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    • pp.14-21
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    • 2000
  • The cavitation noise of 2-D hydrofoils is measured a cavitation tunnel. A new experimental method was developed for the noise measurement of 2-D hydrofoil. Three hydrofoils with the span of 600mm are designed and manufactured to investigate cavitation behavior and noise characteristics. The experimental results show the noise characteristics of various cavitation patterns and the noise performance of the three foils very well. This suggests that low-noise propeller blade section can be developed using the present experimental method.

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The Characteristics of a Pump at Nearly Saturated State

  • Kim, S. N.;Kim, J. C.
    • Nuclear Engineering and Technology
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    • v.30 no.1
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    • pp.40-46
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    • 1998
  • A set of experiments using a 1/10 scale model pump which was manufactured to simulate performance of reactor coolant pump(RCP) of Y.G.N # 3 and 4, was executed in single phase(at atmospheric pressure and room temperature) and near-saturation(300 ~ 600kPa). The pump characteristics in single phase flow was similar to the characteristics of the RCP. The pump characteristic curves at nearly saturated state were correlated in terms of flow coefficient and head coefficient for subcooled temperature using the cavitation number defined as (equation omitted), which can be predicted the cavitation possibility. The pump behavior around the saturated temperature almost consists with single phase behavior until the cavitation occurs(When cavitation occurs. When the flow coefficient is about 0.12), the pump head rapidly degrades. In this situation, subcooled temperature is about 1.8~8$^{\circ}C$ and cavitation number of model pump is 1.0 ~ 1.7.

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Cavitation-erosion Resistance of Stabilized Stainless Steel with Niobium Addition in Sea Water Environment (해수 내 캐비테이션-침식 저항성에 미치는 스테인리스강의 Nb 첨가의 영향)

  • Choi, Yong-Won;Han, Min-Su;Kim, Seong-Jong
    • Journal of the Korean institute of surface engineering
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    • v.49 no.3
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    • pp.274-279
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    • 2016
  • Stainless steel is widely used in various industries due to its excellent anti-corrosion characteristics. However, if the stainless steel is exposed to high speed fluid flow and chloride ion in the marine environment, corrosion and cavitation damage occurred on the surface easily. Therefore, to prevent these problems, stabilzed stainless steel is applied to offshore and shipbuilding industries. In this study, stabilized stainless steel specimen was made by 19%Cr-9%Ni with different Nb contents (0.29%, 0.46% and 0.71%). And then, their cavitation characteristics were investigated. As a result, the characteristics of cavitation resistance of stainless steel could be improved by increasing Nb contents.

A Numerical Study on the Characteristics of Cavitation and Internal Flow According to Nozzle Length-to-Diameter Ratio (노즐 형상비에 따른 캐비테이션 및 내부 유동 특성에 관한 수치적 연구)

  • Han, Dong-Sik;Kim, Hyun-Kyu;Chang, Young-June;Jeon, Chung-Hwan
    • Journal of ILASS-Korea
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    • v.13 no.4
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    • pp.200-205
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    • 2008
  • Spray formation mechanism was controlled by a cavitation inside an injection nozzle. Nozzle geometry affects spray characteristics and formation behavior, which could determine engine performance and pollutant formation. A study was carried out on the influence of aspect ratio on cavitation inside a nozzle. The cavitation model available in Star-CD code was used to obtain cavitation behavior inside nozzle, which was compared with previous experimental results. In this paper, a CFD approach combining multiphase Volume-of-Fluid(VOF) and k-model was applied. The numerical results are similar with the experimental results.

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Numerical Analysis on Flow Characteristics of High Pressure Drop Control Valves with Anti-Cavitation Trim (Anti-Cavitation Trim을 갖는 고차압 제어밸브의 유동특성에 관한 수치해석)

  • Ahn, Y.J.;Kim, B.J.;Shin, B.R.
    • The KSFM Journal of Fluid Machinery
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    • v.10 no.4
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    • pp.61-70
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    • 2007
  • Numerical analysis of three dimensional incompressible turbulent flows in LNG marine high pressure drop control valves was carried out by using the CFD-ACE from ESI-Group. In this study, flow characteristics of control valves with complex flow fields including cavitation effect were investigated. Simulation was performed on five models of control valve that had different orifice diameters of anti-trim and the size of valve. Comparing newly designed control valves for controling the occurrence of cavitation with the conventional valve, new valves showed a improved flow pattern with almost no cavitation.

A Study on the Flow Characteristics of a Butterfly Valve in Fire Protection (소화용 버터플라이 밸브의 유동특성에 관한 연구)

  • 이동명;김엽래
    • Fire Science and Engineering
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    • v.16 no.4
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    • pp.59-64
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    • 2002
  • Investigation of flow characteristics on pressure loss and cavitations of the butterfly valve has been carried out. The pressure loss coefficient on opening angle of valve has been formulated by applying the Carnot's equations. Cavitations (such as cavitation Inception, super cavitation inception, cavitation damage inception, choking cavitation) have been predicted from the pressure loss coefficient of valve. The prediction of pressure loss and cavitation has been carried out change of the thickness ratio on opening angle of valve. The prediction data is utilize to necessary engineering data to develope of the butterfly valve.

Characteristics Evaluation with Cavitation Condition of 304 Stainless Steel in Seawater Environment (해수 환경 하에서 304 스테인리스강의 캐비테이션 조건에 따른 특성 평가)

  • Jang, Seok-Ki;Chong, Sang-Ok;Han, Min-Su;Kim, Seong-Jong
    • Journal of the Korean institute of surface engineering
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    • v.45 no.6
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    • pp.278-283
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    • 2012
  • This investigation evaluated the effect of cavitation condition on electrochemical characteristics of 304 stainless steel, which is widely used for marine environment. The cavitation test with time were conducted on 304 stainless steel in seawater solution. Surface morphologies of specimen were observed by scanning electron microscope (SEM) and 3D microscope. Pitting depth, weight loss and damage rate were analyzed after each cavitation experiment. The surface damage was more severe as the current density increased. A dramatical increase in the damage depth and weight loss was observed after 7 hours of cavitation experiment.

Cavitation Damage Characteristics of Al and Zn Arc Thermal Spray Coating Layers for Hull Structural Steel (선체 구조용 강재에 대한 Al과 Zn 아크용사코팅 층의 캐비테이션 손상 특성)

  • Park, Il-Cho;Kim, Seong-Jong
    • Journal of the Korean institute of surface engineering
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    • v.49 no.1
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    • pp.32-39
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    • 2016
  • In this study, Al and Zn arc thermal spray coatings were carried out onto the substrate of SS400 steel to improve corrosion resistance and durability of hull structural steel for ship in marine environment. Therefore cavitation-erosion test was conducted to evaluate the durability of painted and thermal spray coated specimens. And then the damaged surface morphology and weight loss were obtained to compare with each other, respectively. As a result, the painted specimen was the poorest cavitation resistance characteristics because surface damage behavior appeared to be exfoliated in bulk shape during the cavitation experiment. And Zn thermal spray coating layer presented the significant surface damage depth due to relatively low surface hardness and local cavitation damage tendency. On the other hand, as a result of the weight loss analysis, the painting layer presented the poorest cavitation resistance and the Al thermal spray coating layer relatively showed the best results after cavitation experiment.