• Title/Summary/Keyword: Cavitation

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Study of Cavitation Instabilities in Double-Suction Centrifugal Pump

  • Hatano, Shinya;Kang, Donghyuk;Kagawa, Shusaku;Nohmi, Motohiko;Yokota, Kazuhiko
    • International Journal of Fluid Machinery and Systems
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    • v.7 no.3
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    • pp.94-100
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    • 2014
  • In double-suction centrifugal pumps, it was found that cavitation instabilities occur with vibration and a periodic chugging noise. The present study attempts to identify cavitation instabilities in the double-suction centrifugal pump by the experiment and Computational Fluid Dynamics (CFD). Cavitation instabilities in the tested pump were classified into three types of instabilities. The first one, in a range of cavitation number higher than breakdown cavitation number, is cavitation surge with a violent pressure oscillation. The second one, in a range of cavitation number higher than the cavitation number of cavitation surge, is considered to be rotating cavitation and causes the pressure oscillation due to the interaction of rotating cavitation with the impeller. Last one, in a range of cavitation number higher than the cavitation number of rotating cavitation, is considered to be a surge type instability.

Dynamic Response of Blade Surface Cavitation

  • Toyoshima, Masakazu;Sakaguchi, Kimiya;Tsubouchi, Kota;Horiguchi, Hironori;Sugiyama, Kazuyasu
    • International Journal of Fluid Machinery and Systems
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    • v.9 no.2
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    • pp.160-168
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    • 2016
  • In high speed turbopumps, cavitation occurs and often causes the flow instabilities such as cavitation surge and rotating cavitation. The occurrence of these cavitation instabilities is considered to relate to dynamic characteristics of the cavitation, which are modelled using a cavitation compliance and a mass flow gain factor. Various types of cavitation such as a blade surface cavitation, a tip leakage vortex cavitation, and a backflow vortex cavitation occur at the same time in the inducer and the dynamic characteristics of each cavitation have not been clarified yet in experiments. Focusing on the blade surface cavitation as one of fundamental cavitation, we investigated the dynamic characteristics of the blade surface cavitation on a flat plate hydrofoil in experiments in the present study.

Experimental Study of Discharge Coefficient and Cavitation for Different Nozzle Geometries (노즐 오리피스 형상에 따른 Discharge Coefficient와 Cavitation에 관한 실험적 연구)

  • Kim, Sung-Ryoul;Ku, Kun-Woo;Hong, Jung-Goo;Lee, Choong-Won
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.10
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    • pp.933-939
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    • 2010
  • The purpose of this study is to investigate the generation and development of cavitation in circular and elliptical nozzles. In order to investigate the influence of cavitation, the experiment was conducted with a set of elliptical nozzles that had the same cross-sectional area, different orifice aspect ratios (a/b). Each nozzle was made of acrylic so that visualization was possible. With the injection pressure, the internal flow of the nozzle was classified into the no-cavitation, cavitation, and hydraulic-flip regions. Regardless of the nozzle geometry, with the injection pressure, the flow rate in the no-cavitation and cavitation regions increased and the discharge coefficient decreased. However, the flow rate was constant in the hydraulic-flip region. In the elliptical nozzles, the generation and development of cavitation occurred at higher cavitation number than that in the case of a circular nozzle.

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

  • Yamamoto, Kazuyoshi;Tsujimoto, Yoshinobu
    • International Journal of Fluid Machinery and Systems
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    • v.2 no.1
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    • pp.40-54
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    • 2009
  • Cavitation instabilities in turbo-machinery such as cavitation surge and rotating cavitation are usually explained by the quasi-steady characteristics of cavitation, mass flow gain factor and cavitation compliance. However, there are certain cases when it is required to take account of unsteady characteristics. As an example of such cases, cavitation surge in industrial centrifugal pump caused by backflow vortex cavitation is presented and the importance of the phase delay of backflow vortex cavitation is clarified. First, fundamental characteristics of backflow vortex structure is shown followed by detailed discussions on the energy transfer under cavitation surge in the centrifugal pump. Then, the dynamics of backflow is discussed to explain a large phase lag observed in the experiments with the centrifugal pump.

Numerical Analysis of the Influence of Acceleration on Cavitation Instabilities that arise in Cascade

  • Iga, Yuka;Konno, Tasuku
    • International Journal of Fluid Machinery and Systems
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    • v.5 no.1
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    • pp.1-9
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    • 2012
  • In the turbopump inducer of a liquid propellant rocket engine, cavitation is affected by acceleration that occurs during an actual launch sequence. Since cavitation instabilities such as rotating cavitations and cavitation surges are suppressed during launch, it is difficult to obtain data on the influence of acceleration on cavitation instabilities. Therefore, as a fundamental investigation, in the present study, a three-blade cyclic cascade is simulated numerically in order to investigate the influence of acceleration on time-averaged and unsteady characteristics of cavitation that arise in cascade. Several cases of acceleration in the axial direction of the cascade, including accelerations in the upstream and downstream directions, are considered. The numerical results reveal that cavity volume is suppressed in low cavitation number condition and cavitation performance increases as a result of high acceleration in the axial-downstream direction, also, the inverse tendency is observed in the axial-upstream acceleration. Then, the regions in which the individual cavitation instabilities occur shift slightly to a low-cavitation-number region as the acceleration increases downstream. In addition, in a downstream acceleration field, neither sub-synchronous rotating cavitation nor rotating-stall cavitation are observed. On the other hand, rotating-stall cavitation occurs in a relatively higher-cavitation-number region in an upstream acceleration field. Then, acceleration downstream is robust against cavitation instabilities, whereas cavitation instabilities easily occur in the case of acceleration upstream. Additionally, comparison with the Froude number under the actual launch conditions of a Japanese liquid propellant rocket reveals that the cavitation performance will not be affected by the acceleration under the current launch conditions.

Experimental Study on the Cavitation Noise of a Hydrofoil (3차원 날개의 캐비테이션 소음 계측시험)

  • Lee, Seung-Jae;Seo, Jong-Soo;Han, Jae-Moon
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.2
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    • pp.111-118
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    • 2007
  • In order to investigate the noise characteristics of the different caviation, noise measurements were carried out in a large cavitation tunnel of the Samsuug Ship Model Basin(SSMB). The noise measurements for a 3-dimensional hydrofoil were carried out at the angle of attack of $12^{\circ}$ and $16^{\circ}$ according to the decrease in cavitation number. It is exhibited that sound pressure level(SPL) increased sharply with cavitation inception. The frequency of the noise induced by sheet cavitation was higher than that of tip vortex cavitation in the phase of cavitation inception. Within the range of the high frequency, in the case of fully developed cavitation, sheet cavitation noise was significantly increased in sound pressure level compared with tip vortex cavitation noise. In this study, the noise characteristics of the different cavitation types were considered experimentally and would be utilized as a basis for the analysis of propeller cavitation noise.

A Study on the Damage Suppression of Diesel Engine Cylinder Liners under Vibratory Cavitation (디젤기관 실린더라이너의 진동캐비테이션 손상 억제에 관한 연구)

  • Jeong, Ki-Cheol;Hwang, Jae-Ho;Lim, Uh-Joe
    • Journal of Fisheries and Marine Sciences Education
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    • v.10 no.2
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    • pp.226-238
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    • 1998
  • With the advent of high speed and high output diesel engines, cavitation erosion-corrosion of wet cylinder liners is one of the most prevalent types of failure. The cavitation erosion-corrosion at cylinder liners in water cooled diesel engines is considered to be to the collapse of cavitation bubbles attributed to the cylinder liner vibration. To suppress cavitation damage in cylinder liner, the addition of an inhibitor would be more general method and innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. In this study, photomicrographs from vibratory facility cavitation specimens and from an eroded liner of a field diesel engine are compared. The behavior of cavitation bubbles grown in fluid is observed under vibration conditions by taking direct photographs with high speed camera. In order to determine the contributions of pure cavitation erosion and of pure corrosion to the total cavitation damage are be studied by following an experimental programme which includes three types of test: (1)pure cavitation erosion test, (2)pure corrosion test, and (1)cavitation erosion-corrosion test. Also cavitation damage under vibratory cavitation is reduced by using flow in tap water.

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Numerical Analysis of Tip Vortex Cavitation Behavior and Noise on Hydrofoil using Dissipation Vortex Model and Bubble Theory (소산이 고려된 보오텍스 모델과 버블 이론을 이용한 수중익 날개 끝 보오텍스 캐비테이션 거동 및 소음의 수치적 해석)

  • Park, Kwang-Kun;Seol, Han-Shin;Lee, Soo-Gab
    • Journal of the Society of Naval Architects of Korea
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    • v.43 no.2
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    • pp.177-185
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    • 2006
  • Cavitation is the dominant noise source of the marine vehicle. Of the various types of cavitation , tip vortex cavitation is the first appearance type of marine propeller cavitation and it generates high frequency noise. In this study, tip vortex cavitation behavior and noise are numerically investigated. A numerical scheme using Eulerian flow field computation and Lagrangian particle trace approach is applied to simulate the tip vortex cavitation on the hydrofoil. Vortex flow field is simulated by combined Moore and Saffman's vortex core radius equation and Sculley vortex model. Tip vortex cavitation behavior is analyzed by coupled Rayleigh-Plesset equation and trajectory equation. The cavitation nuclei are distributed and released in the vortex flow result. Vortex cavitation trajectories and radius variations are computed according to nuclei initial size. Noise is analyzed using time dependent cavitation bubble position and radius data. This study may lay the foundation for future work on vortex cavitation study and it will provide a basis for proper underwater propeller noise control strategies.

Cavitation studies on axi-symmetric underwater body with pumpjet propulsor in cavitation tunnel

  • Suryanarayana, Ch.;Satyanarayana, B.;Ramji, K.;Rao, M. Nageswara
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.2 no.4
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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.

A cavitation performance prediction method for pumps: Part2-sensitivity and accuracy

  • Long, Yun;Zhang, Yan;Chen, Jianping;Zhu, Rongsheng;Wang, Dezhong
    • Nuclear Engineering and Technology
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    • v.53 no.11
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    • pp.3612-3624
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    • 2021
  • At present, in the case of pump fast optimization, there is a problem of rapid, accurate and effective prediction of cavitation performance. In "A Cavitation Performance Prediction Method for Pumps PART1-Proposal and Feasibility" [1], a new cavitation performance prediction method is proposed, and the feasibility of this method is demonstrated in combination with experiments of a mixed flow pump. However, whether this method is applicable to vane pumps with different specific speeds and whether the prediction results of this method are accurate is still worthy of further study. Combined with the experimental results, the research evaluates the sensitivity and accuracy at different flow rates. For a certain operating condition, the method has better sensitivity to different flow rates. This is suitable for multi-parameter multi-objective optimization of pump impeller. For the test mixed flow pump, the method is more accurate when the area ratios are 13.718% and 13.826%. The cavitation vortex flow is obtained through high-speed camera, and the correlation between cavitation flow structure and cavitation performance is established to provide more scientific support for cavitation performance prediction. The method is not only suitable for cavitation performance prediction of the mixed flow pump, but also can be expanded to cavitation performance prediction of blade type hydraulic machinery, which will solve the problem of rapid prediction of hydraulic machinery cavitation performance.