The flow structure in the near field of jets and its effect on cavitation inception


Journal Article

Cavitation experiments performed in the near field of a 50mm diameter (D) jet at Re D = 5 × 10 5 , showed inception in the form of inclined 'cylindrical' bubbles at axial distances (x/D) less than 0.55, with indices of 2.5. On tripping the boundary layer, cavitation inception occurred at x/D ≈2, as distorted 'spherical' bubbles with inception indices of 1.7. To investigate these substantial differences, the near field of the jet was measured using PIV. Data on the primary flow, the strength distribution of the 'streamwise' vortices and the velocity profiles within the initial boundary layers were obtained. The untripped case showed a direct transition to three-dimensional flow in the near field (x/D < 0.7) even before rolling up to distinct vortex rings. Strong 'streamwise' vortices with strengths up to 25% of the jet velocity times the characteristic wavelength were seen. Cavitation inception occurred in the core of these vortices. In contrast, in the tripped jet the vortex sheet rolled up to the familiar Kelvin-Helmholtz vortex rings with weak secondary vortices. Using the measured nuclei distribution, strengths and straining of the 'streamwise' structures, the rates of cavitation events were estimated. The estimated results match very well the measured cavitation rates. Also, the Reynolds stresses in the near field of the jet show similar trends and magnitudes to those of Browand & Latigo (1979) and Bell & Mehta (1990) for a plane shear layer.

Full Text

Duke Authors

Cited Authors

  • Gopalan, S; Katz, J; Knio, O

Published Date

  • November 10, 1999

Published In

Volume / Issue

  • 398 /

Start / End Page

  • 1 - 43

International Standard Serial Number (ISSN)

  • 0022-1120

Digital Object Identifier (DOI)

  • 10.1017/S0022112099006072

Citation Source

  • Scopus