• Title/Summary/Keyword: Cavitation characteristics

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An Experimental Study on Noise Characteristics of Propeller Cavitation Inception (프로펠러 캐비테이션의 초기발생과 소음특성에 대한 실험연구)

  • Lee, Phil-Ho;Ahn, Byoung-Kwon;Lee, Chang-Sup;Lee, Jung-Hoon
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.1
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    • pp.1-7
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    • 2011
  • Cavitation is the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Various types of cavitations are generated on the propeller blades. As cavity bubbles passing the blade are forced to oscillate in size or shape and come to collapse, they cause very strong local acoustic waves in the fluid and radiate noise. Comparing the Sound Pressure Level(SPL) before and after cavitation, SPL increases 2dB per 1 knot increase in ship speed above the cavitation inception speed(CIS). Consequently, the CIS is an important criteria to design silent propellers. In this work, experimental measurements of radiated noise according to various types of cavitations from the model propeller are carried out in a large cavitation tunnel and their acoustical characteristics are extensively investigated.

Experimental Study on the Unsteady Cavitation of Turbopump Inducer (터보펌프 인듀서의 비정상 캐비테이션에 관한 실험적 연구)

  • Hong, Soon-Sam;Kim, Jin-Sun;Choi, Chang-Ho;Kim, Jin-Han
    • The KSFM Journal of Fluid Machinery
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    • v.8 no.1 s.28
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    • pp.23-29
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    • 2005
  • Steady and unsteady cavitation characteristics of turbopump inducer were investigated in this paper. To investigate the effect of blade angle on the inducer performance, three inducers with inlet tip blade angle of $7.8^{\circ},\;7.0^{\circ},\;6.1^{\circ}$, respectively, were tested. For $7.8^{\circ},\;7.0^{\circ}$ inducers in the non-cavitating condition, head decreased linearly with flow rate, but head-flow rate curve had a dip at the flow coefficient ${\psi}=0.065$ for $6.1^{\circ}$ inducer. Attached cavitation and cavitation surge were found in the $7.8^{\circ},\;7.0^{\circ}$ inducers in the cavitation tests. During the attached cavitation one cell rotated at the same rotational speed as that of the inducer. The cavitation surge did not rotate and the oscillating frequency was $7{\sim}20\;Hz$. From the curve of the critical cavitation number versus flow rate, it was found that the steady cavitation performance of $6.1^{\circ}$ inducer was much lower than that of $7.8^{\circ},\;7.0^{\circ}$ inducers.

Experimental Study on Cavitation Instability of a Solution Pump Inducer in an Absorption Chiller-Heater (흡수식 냉온수기내 용액펌프 Inducer의 Cavitation 불안정성에 대한 실험적 연구)

  • Seo, Min;Lee, Kyung-Hoon;Kang, Shin-Hyung
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2434-2439
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    • 2008
  • This paper was studied on the cavitation instability of a Solution Pump Inducer in an absorption chiller-heater. Inlet pressure of LiBr and rotational speed at nominal mode are 2,800 Pa and 3,500 rpm respectively. Due to the marginal operation of available NPSH, the cavitation performance of the inducer is critical for the stable operation without the deterioration of head performance. In the study, cavitation performance and its mode of instability was investigated experimentally. Water was used as the working fluid and the test inducer was scaled up as 1.75 times for detail measurements and flow visualization. Inlet pressure was controlled by a vacuum pump. This research focused on types of cavitation instability and phenomena to investigate the possibility of harmful damage due to cavitation instability. Casing wall pressure and instantaneous inlet pressure was measured to observe the unsteady flow characteristics. Through the visualization and spectrum analysis of pressure, the occurrence region and intensity of asymmetric cavitation and cavitation surge are analyzed in the test inducer.

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Experimental Study on the Unsteady Cavitation of Turbopump Inducer (터보펌프 인듀서의 비정상 캐비테이션에 관한 실험적 연구)

  • Hong, Soon-Sam;Kim, Jin-Sun;Choi, Chang-Ho;Kim, Jin-Han
    • 유체기계공업학회:학술대회논문집
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    • 2003.12a
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    • pp.333-339
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    • 2003
  • Steady and unsteady cavitation characteristics of turbopump inducer were investigated in this paper. To see the effect of blade angle on the inducer performance, three inducers with inlet tip blade angle of $7.8^{\circ},\;7.0^{\circ},\;6.1^{\circ}$, respectively, were tested. For $7.8^{\circ},\;7.0^{\circ}$ inducers in the non-cavitating condition, head decreased linearly with flow rate, but head-flow rate curve had a dip at the flow coefficient ${\Phi}=0.065\;for\;6.1^{\circ}$ inducer. Rotating cavitation and cavitation surge were found in the $7.8^{\circ},\;7.0^{\circ}$ inducers in the cavitation tests. During the rotating cavitation one cell rotated at the same rotational speed as that of the inducer. The cavitation surge did not rotate and the oscillating frequency was $7{\sim}20\;Hz$. From the curve of the critical cavitation number versus flow rate, it was found that the steady cavitation performance of $6.1^{\circ}$ inducer was much lower than that of $7.8^{\circ},\;7.0^{\circ}$ inducers.

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Characteristics of Gap Flow of a 2-Dimensional Horn-Type Rudder Section (2차원 혼 타 단면의 간극유동 특성에 대한 연구)

  • Choi, Jung-Eun;Chung, Seok-Ho
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.2 s.152
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    • pp.101-110
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    • 2007
  • Recently, rudder erosion due to cavitation frequently has occurred at large high speed container carriers. Especially, in the case of a horn-type rudder, the rudder erosion is severe around a gap. The gap-flow characteristics are investigated through a computational method to understand the effects of a gap on the cavitation and rudder efficiency. A viscous flow theory utilizing a cavitation model is applied to calculate the flow around idealized 2-dimensional rudder sections in a full scale. The effects of gap clearance and flow-control projection are also investigated. From the computational results, the mass flow rate through a gap is found to be one of the important parameters to affect the cavitation and rudder efficiency.

Characteristics of Cavitation Noise on High-Speed Propellers (고속 프로펠러의 캐비테이션 소음 특성)

  • I.H. Song;J.W. Ahn;K.S. 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.22-29
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    • 2000
  • The cavitation noised of high-speed propellers was experimentally studied in KRISO cavitation tunnel. In this paper, a series of cavitation noise tests were carried out for five propellers with various sections and loading distributions. From the experimental results, the noise characteristics of various cavitation pattern and the noise performance of the propellers were analyzed. There can be used for optimum design for high-speed propellers.

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A Study on the Characteristics of Cavitation Erosion of Super Duplex Stainless Steel (슈퍼 듀플렉스 스테인리스강의 캐비테이션 마모 특성에 대한 연구)

  • Jeon, Soon-Hyeok;Kim, Soon-Tae;Lee, In-Sung;Park, Yong-Soo
    • Journal of Korea Foundry Society
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    • v.30 no.4
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    • pp.142-146
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    • 2010
  • To elucidate the characteristics of cavitation erosion of super duplex stainless steel, a cavitation erosion test, an optical microstructure, a hardness test, and a transmission electron microscope (TEM) analysis were conducted. As aging time at $475^{\circ}C$ increased, the hardness of ferrite phase increased whereas that of austenite phase was nearly constant. The reason why the cavitation erosion resistance increased with an increase of aging time was due to the formation of W-rich phases (${\alpha}$') of a nanometer scale with the high hardness that were precipitated within ${\alpha}$-grains and at ${\alpha}$-grain boundaries during aging, compared with that of the solution annealed alloy.

Cavitation-Erosion Characteristics between Polymer Based Composites and Metals under the Various Condition of Fluid Systems (유체 환경하에서의 고분자 기지 복합재료와 금속재의 캐비테이션 침식 특성)

  • Kim, Yun-Hae;Son, Young-Jun;Eum, Soo-Hyun;Lee, Jung-Ju
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.3
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    • pp.363-371
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    • 2003
  • This study is mainly concerned with phenomenon of cavitation-erosion on the several materials and corrosive liquids which were applied with vibrator(suggested by ASTM G 32, 20KHz, 50$mu extrm{m}$). The maximum erosion rate by cavitation erosion in both of distilled water and sea water appeared to be proportioned to their hardness and tensile strength. Cavitation weight loss and rate of cast iron in sea water condition were greater(approximately 3 times) than that in distilled water condition, however in case of stainless steel and brass the cavitation weight loss of composite materials were not so different in both of their conditions. Cavitation weight loss of composite materials were shown as below on this test, Duratough DL : Weight loss in sea-water condition were greater (approximately 2.3 times) than it's distilled water condition. The main tendency of cavitation erosion for metals appeared that small damaged holes causing by cavitation erosion was observed with radial pattern. On the other hand, the tendency for composites appeared that small damaged holes were observed randomly.

Cavitation state identification of centrifugal pump based on CEEMD-DRSN

  • Cui Dai;Siyuan Hu;Yuhang Zhang;Zeyu Chen;Liang Dong
    • Nuclear Engineering and Technology
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    • v.55 no.4
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    • pp.1507-1517
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    • 2023
  • Centrifugal pumps are a crucial part of nuclear power plants, and their dependable and safe operation is crucial to the security of the entire facility. Cavitation will cause the centrifugal pump to violently vibration with the large number of vacuoles generated, which not only affect the hydraulic performance of the centrifugal pump but also cause structural damage to the impeller, seriously affecting the operational safety of nuclear power plants. A closed cavitation test bench of a centrifugal pump is constructed, and a method for precisely identifying the cavitation state is proposed based on Complementary Ensemble Empirical Mode Decomposition (CEEMD) and Deep Residual Shrinkage Network (DRSN). First, we compared the cavitation sensitivity of pressure fluctuation, vibration, and liquid-borne noise and decomposed the liquid-borne noise by CEEMD to capture cavitation characteristics. The decomposition results are sent into a 12-layer deep residual shrinkage network (DRSN) for cavitation identification training. The results demonstrate that the liquid-borne noise signal is the most cavitation-sensitive signal, and the accuracy of CEEMD-DRSN to identify cavitation at different stages of centrifugal pumps arrives at 94.61%

Design of Cavitation-Resistive Pump Inducer (공동현상을 고려한 펌프 인듀서 설계)

  • Jung, Keun-Hwa;Ahn, Kwang-Woon;Lee, Seungbae;Kim, Jin-Hwa;Kang, Shin-Hyoung
    • 유체기계공업학회:학술대회논문집
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    • 2001.11a
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    • pp.185-190
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    • 2001
  • The cavitation causes suction performance and efficiency of the high-speed pump to be reduced significantly To diminish these effects, the inducer has been used. Most of the inducer is designed at a maximum efficiency point of the pump, therefore suction performance drop due to effects of flow separation and inlet inverse flow is often observed at off-design point. The objective of this study is to find out the cavitation modes at various conditions by applying event detection technique and to design an inducer reducing cavitation. The pressure fluctuations at each cavitating condition were measured at inducer inlet and outlet locations using pressure transducers, which were located 90 degrees apart from each other to identify the cavitation modes. The time-frequency characteristics were analyzed by using Choi-williams distribution. In the second part of this paper, the inducer design method which uses nominal performance characteristic and onset condition of cavitation is introduced and applied to real situation.

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