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2003 Fiscal Year Final Research Report Summary

Proposition of a rip-off model at the point of flow separation as a new mechanism of cavitation inception

Research Project

Project/Area Number 13450066
Research Category

Grant-in-Aid for Scientific Research (B)

Allocation TypeSingle-year Grants
Section一般
Research Field 設計工学・機械要素・トライボロジー
Research InstitutionOkayama University

Principal Investigator

WASHIO Seiichi  OKAYAMA UNIVERSITY, Faculty of Engineering, Professor, 工学部, 教授 (20026222)

Co-Investigator(Kenkyū-buntansha) YOSHIDA Atsumasa  Osaka Prefecture University, Professor, 大学院・工学研究科, 教授 (60174918)
TAKAHASHI Satoshi  OKAYAMA UNIVERSITY, Faculty of Engineering, Assistant Professor, 工学部, 助教授 (20236277)
Project Period (FY) 2001 – 2003
KeywordsCavitaion / Hydraulic oil / Point of flow separation / Light emission / Electrification / Heat generation / Microscope / Absolute negative pressure
Research Abstract

1. Trough microscopic observations on the point of separation in various hydraulic oil flows, it has been confirmed that the very first cavitation starts with a microscopic cavity which suddenly emerges on the wall near the point of separation, where the flow is laminar. A cavity suddenly emerges and rapidly grows, in 0.1 millisecond for example, with its upstream tip attached on the wall and elongates about 45 degrees away from the surface. This incipient cavity produces many minute bubbles, which act as so-called cavitation nuclei in the downstream turbulence.
2. Light emission and electrical charges are always observed in vigorous cavitation in hydraulic oil flows. Oil and the wall put on charges with opposite signs when cavitation starts. The spectrum of light emission suggests that it occurs when accumulated electrical charges are discharged in a near-vacuum cavity.
3. A separation streamline is spontaneously visualized in a hydraulic oil flow. Through measurements, it has proved that heat is generated at the point of separation and accordingly temperature becomes higher along the streamline extending from the separation point. The fact shows that a streamline becomes visible owing to differences of refractive index generated by this temperature distribution.
4. The most important result of our research is as follows ; the real cause of cavitation is "the singularity of the point of flow separation". When a flow rate increases, the solid-liquid interface at the point of separation is suddenly destroyed, producing a rift there. The rift develops into an incipient cavity, which we could clearly observe in the present research.
What is the destruction of the solid-liquid interface? What is the major cause of it? Stress concentration, heat generation or tensile stress? Our next target of research is to make clear these questions.

  • Research Products

    (12 results)

All Other

All Publications (12 results)

  • [Publications] 鷲尾誠一, 吉森修一, 高橋智: "円筒面絞りを使った油のキャビテーション観察(はく離面が滑らかで初生気泡が停留できない場合)"キャビテーションに関するシンポジウム(第11回). 39-42 (2001)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] S.Washio, S.Takahashi, S.Kawahara, M.Kishitani: "Study on the cavitation mechanism in hydraulic oil flow using a needle projection"Proceedings of the Institution of Mechanical Engineers, Part J : Journal of Engineering Tribology. Vol.216. 27-34 (2002)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 鷲尾 誠一, 高橋 智, 吉森 修一: "滑らかな面からはく離する油の流れにおける初生空洞が停留しないキャビテーションの観察"日本機械学会論文集(B編). 69巻,681号. 1120-1127 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] S.Washio, S.Takahashi, S.Yoshimori: "Study on cavitation starting at the point of separation on a smooth wall in hydraulic oil flow"Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science. Vol.217. 619-630 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] S.Takahashi, S.Washio, K.Uemura, A.Okazaki: "Experimental study on cavitation starting at and flow characteristics close to the point of separation"Fifth International Symposium on Cavitation (CAV2003). (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 岡崎全伯, 鷲尾誠一, 高橋智: "様々な絞りを用いた油のキャビテーション初生の観察"日本機械学会中国四国支部第42期総会・講演会講演論文集. 129-130 (2004)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Seiichi WASHIO, Shuichi YOSHIMORI, Satoshi TAKAHASHI: "Observation of Cavitation in Hydraulic Oil Flow through Constriction with Smooth Cylindrical Surface Where Incipient Cavity Is Unable to Stay"The 11th symposium of cavitation. 39-42 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Seiichi WASHIO, Satoshi TAKAHASHI, Shinichiro KAWAHARA, Masanori KISHITANI: "Study on the cavitation mechanism in hydraulic oil flow using a needle projection"Proceedings of the Institution of Mechanical Engineers, Part J : Journal of Engineering Tribology. Vol.216. 27-34 (2002)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Seiichi WASHIO, Satoshi TAKAHASHI, Shuichi YOSHIMORI: "Observation of Cavitation in Hydraulic Oil Flow Separated from a Smooth Surface on Which an Incipient Cavity Is Unable to Stay"Transactions of the Japan Society of Mechanical Engineers (B). 1120-1127 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Seiichi WASHIO, Satoshi TAKAHASHI, Shuichi YOSHIMORI: "Study on cavitation starting at the point of separation on a smooth wall in hydraulic oil flow"Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science. vol.217. 619-630 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Satoshi TAKAHASHI, Seiichi WASHIO, Kazuhiro UEMURA, Akinori OKAZAKI: "Experimental study on cavitation starting at and flow characteristics close to the point of separation"Fifth International Symposium on Cavitation (CAV2003). (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Akinori OKAZAKI, Seiichi WASHIO, Satoshi TAKAHASHI: "Observation of Cavitation Inception in Hydraulic Oil Flows through Various Constrictions"The conference of JSME, Hiroshima,. 129-130 (2004)

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 2005-04-19  

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