• 대한조선학회논문집
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• 제46권6호
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• pp.569-577
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• 2009

As the scale factor of model propellers utilized in cavitation test is about 40, it is difficult to find out practical countermeasures against the small area erosions on the blade tip region throughout model erosion tests. In this study, a partial propeller blade model was used for the observation of cavitation pattern for the eroded propeller. A partial propeller blade model was manufactured from 0.7R to tip with expanded profile and with adjustable device of angle of attack. Reynold's number of a partial propeller blade model is 7 times larger than that of a model propeller. Also, anti-singing edge and application of countermeasures to partial propeller blade model which produced in large scale can be more practical than a model propeller. For the observation of cavitation at high Reynold's number, high speed cavitation tunnel was used. To find out the most severe erosive blade position during a revolution, cavitation observation tests were carried out at 5 blade angle positions.

• 수산해양기술연구
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• 제25권4호
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• pp.209-213
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• 1989

이상으로부터 부분 캐비테이션이 발생하는 익형에 대하여 지금까지 사용된 경계층 제어법과는 달리 전자력 가속에 의하여 익형의 전연 부근에서 흐름을 가속시킨 결과 경계층의 억제에 의해 부분 캐비테이션의 두께 및 길이가 다소 감소하였음을 알 수 있었다. 앞으로의 연구는 캐비테이션의 종류 및 조건들에 맞는 최적의 유동속도 가속장치 설계가 이루어 져야 할 것으로 생각된다.

• International Journal of Fluid Machinery and Systems
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• 제3권2호
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• pp.129-136
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• 2010

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of flow field between in the cavitating and no-cavitating conditions.

• Journal of Advanced Marine Engineering and Technology
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• 제12권1호
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• pp.53-61
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• 1988

Most of the recent for the flow field hydrofoil in partially cavitating condition are the ones which are linearized, and the problem of cavity end region for hydrofoil is not verified. This paper deals with a study on characteristics of end region flow field for partially cavitating hydrofoil by using a characteristics of shear turbulence flow and nonlinear cavity flow theory. The results obtained as follows : 1) Shear layer thickness is decreased gradually going to the end section of hydrofoil. When attack angle is large, it is appeared largely at the region of partial cavitation after its collapsing. 2) The fluctuation velocity of a second-degree relative direction have minimum value at the front of hydrofoil or at the end of hydrofoil. The difference for the validity of attack angle is appeared largely at the surrounding of .chi.$_{e}$ point. 3) The fluctuation velocity of transverse direction decrease from the maximum thickness of cavitation to the end of hydrofoil, but it undergoes largely the effect of pressure recovery. The difference is larger at the region of partial cavitation after its collapsing than at the of hydrofoil. 4) The distribution of Reynolds stress have maximum values at the region of partial cavitation after its collapsing and the end of foil, and the larger attack angle, the larger the distribution of value.e.

• 한국음향학회지
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• 제33권6호
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• pp.358-365
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• 2014

선박용 프로펠러가 수중에서 빠른 속도로 회전할 때, 날개 표면의 국부적인 압력이 낮아짐에 따라 불가피하게 여러 형태의 공동이 발생한다. 이러한 공동현상은 근본적으로 날개 단면의 기하학적 형상 특성과 수동력학적 운용조건에 의해 결정되며, 결과적으로 선박 프로펠러에서 유기되는 수중방사소음은 공동의 발생특성과 직결된다고 할 수 있다. 따라서 저소음 프로펠러 설계를 위해서는 날개 단면의 형상에 따라 발생하는 공동과 그에 따른 소음특성을 이론 및 실험을 통해 정량적으로 평가할 수 있어야 한다. 본 연구에서는 저소음 프로펠러의 설계단계에서부터 적용이 가능한 부분공동성능 해석법 개발 및 날개단면 형상정보 도출을 목표로 선박용 프로펠러 날개 단면에서 발생하는 부분공동 다상 유동의 비점성 수치해석을 수행하였다. 또한 점성해석 상용프로그램인 FLUENT에서 제공하는 난류 및 공동 모델 조합에 따른 결과를 살펴보았으며, 점성 및 비점성 해석 결과를 비교, 평가 하였다.

• 한국유체기계학회 논문집
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• 제18권4호
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• pp.49-55
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• 2015

The pumped storage plant operates with quick change of the discharge as well as quick changes between pump mode and turbine mode. This study focuses on the cavitation analysis of a pump-turbine model because in turbo-machinery, cavitation can reduce the performance and shorten service life. The pump-turbine model system consists of 7 blades, 20 stay vanes (including tongue) and 20 guide vanes. This study adopts the Rayleigh-Plesset model as a cavitation model, which illustrates cavitation by using the air volume fraction method. The pump mode and turbine mode at the operating condition of partial loading, normal and excessive loading are analyzed to investigate the cavitation performance of the pump-turbine. It was observed that this pump-turbine design showed very good cavitation characteristics with no cavitation bubbles in all operating conditions. Overall value of air volume fraction of both mode at different operating condition are lower than 1, which confirms low possibility of cavitation occurrence at current situation.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.776-781
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• 2005

Cavitation is the most serious problem caused in developing high-speed turbopump, and use of an inducer is often made to avoid cavitation in main impeller. Thus, the inducer always operates under the worst condition of cavitation. If it could be possible to control and suppress cavitation in the inducer by some new device, it would also be possible to suppress cavitation occurring in all types of pumps. The purpose of our present study is to develop a new effective method of controlling and suppressing cavitation in an inducer using shallow grooves, named as "J-Groove", J-Groove is installed on the casing wall near the blade tip to use the pressure difference between high pressure region and low pressure region in the axial direction at the inlet of the inducer. The results show that proper combination of backward-swept inducer with J-Groove improves suction performance of turbopump remarkably in the range of partial flow rate as well as designed flow rate. The rotating backflow cavitation occurring in the range of low flow rate and the cavitation surge occurring in the vicinity of the best efficiency point can be almost fully suppressed by installing J-Groove.

• 대한기계학회논문집B
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• 제29권11호
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• pp.1239-1247
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• 2005

Cavitation is the most serious problem in developing high-speed turbopump, and inducer is often used to avoid cavitation in main impeller. Thus, inducer is always operating in the worst .cavitation condition. If it is possible to control and suppress cavitation in inducer by some new device, it might be possible to suppress cavitation occurring in any type of pumps. The purpose of present study is to develop a new effective method of controlling and suppressing cavitation in inducer using shallow grooves, which is named 'J-Groove'. J-Groove is installed on the casing wall near the blade tip to use the pressure difference between high pressure region and low pressure region of the inducer in an axial direction. The results show that proper combination of backward-swept inducer with J-Groove improves suction performance of turbopump remarkably in the range of partial flow rate as well as designed flow rate. The rotating backflow cavitation occurring in the range of low flow rate and the cavitation surge occurring in the vicinity of the best efficiency point can be almost suppressed by installing J-Groove.

• International Journal of Fluid Machinery and Systems
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• 제1권1호
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• pp.38-46
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• 2008

Studies on cavitation instabilities of hydrofoils and cascades are reviewed to obtain fundamental understandings of the instabilities observed in turbopump inducers. Most of them are based on the stability analysis of two-dimensional inviscid cavitating flow. The most important finding of the analysis is that the cavitation instabilities depend only on the mean cavity length. For a hydrofoil, the characteristic length is the chord length and partial/transitional cavity oscillation occurs with shorter/longer cavity than 75% of the chord length. For cascades, the characteristic length is the blade spacing and various modes of instabilities are predicted when the mean cavity is longer than 65% of the spacing. In the last part, rotating choke is shown to occur when the cavity becomes longer than the spacing.

• International Journal of Fluid Machinery and Systems
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• 제3권1호
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• pp.50-57
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• 2010

The attachment of inducer in front of main impeller is a powerful method to improve cavitation performance. Cavitation surge oscillation, however, often occurs at partial flow rate and extremely low suction pressure. As the cavitation surge oscillation with low frequency of about 10 Hz occurs in a close relation between the inlet backflow cavitation and the growth of blade cavity into the throat section of blade passage, one method of installing an axi-asymmetrical plate upstream of inducer has been proposed to suppress the oscillation. The inlet flow distortion due to the axi-asymmetrical plate makes different elongations of cavities on all blades, which prevent the flow from becoming simultaneously unstable at all throat sections. In the present study, changes of the suppression effects with the axial distance between the inducer inlet and the plate and the changes with the blockage ratios of plate area to the cross-sectional area of inducer inlet are investigated for helical inducers with tip blade angles of $8^{\circ}$ and $14^{\circ}$. Then a conceivable application will be proposed to suppress the cavitation surge oscillation by installing axi-asymmetrical inlet plate.