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An Experimental Investigation on the Effects of Artificial Cavitation Generators on Control and Stabilization of Cloud Cavitation

Shiraghaee Koutenaee, Shahab | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50702 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Javadi, Khodayar
  7. Abstract:
  8. The present study is aimed at investigating experimental methods to control and stabilize the oscillatory effects of sheet/cloud cavitation. Two methods were investigated: The use of artificial cavitation generating appendages, which had a two dimensional geometry similar to that of vortex generators. Employing air injection into the cavity from different locations on the chord of the hydrofoil and a comparison of the stability achieved from each case by analyzing pictures captured from a high-speed camera. To conduct these experiments, a cavitation tunnel along with measurement devices were used. Four different appendages were tested as artificial cavitation generators, which were in two different sizes and mounted in two different locations of the hydrofoil. A NACA-0015 hydrofoil was employed as a basis for the application of the mentioned appendages. The results showed the effect of the size and location of these appendages on the quality of control obtained on the oscillatory behavior of attached cavity. In proper size and location, the appendages could transform the attached sheet/cloud cavitation into travelling two-phase vortex cavitation which is of a bubble dominant nature. According to the mean pressure measurements on the surface of the hydrofoil, it was found out that the appendages could improve the performance of the hydrofoil under cavitating conditions and in some cases, they could even retain the performance under conditions close to non-cavitating regime. In the case of a poor choice for the size and location of the appendages, they would either have no significant influene on the control of cavitation, or have a completely adverse effect on the flow over the hydrofoil and cause stall, which would change the overall performance of the latter. Furthermore, it was concluded that the injection of a bigger volume of air into the cavity would result in more stability of partial cavitation. In order to obtain the same level of stability, less air volume was needed to be injected from locations closer to the leading edge, compared to the ones located downstream. It was concluded from this result that the lateral coverage of the injected air, over the span of the hydrofoil, plays a vital role in control and blockage of the re-entrant jet’s movement toward the leading edge of the hydrofoil, which consequently has an undeniable effect on the control and stabilization of cloud cavitation. This marks the importance of the geometry of the injection holes. Regarding the destructive effects of cavitation, both on the hydrodynamic performance and the structure of the body, the control and stabilization of this phenomenon can reduce these destructive behaviours. Thus, the conclusions reached in this investigation can be applied as solutions to the problem of oscillatory cavitation
  9. Keywords:
  10. Sheet Cavitation ; Sheet/Cloud Cavitation ; Cavitation Control ; Re-Entrant Jet ; Artificial Cavitation Generator ; Vortex Cavitation

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