Murray S. Korman
Dept. of Phys., U. S. Naval Academy, Annapolis, MD 21402
It has been demonstrated that the near-field pressure spectrum (generated by a turbulent submerged water jet) is enhanced when the turbulent flow is modified to become a two-phase flow containing air bubbles [``Proceedings of the 14th ICA, Beijing, China,'' Acoustica 76, supplement to No. 4, May (1992), paper B6-1, p. 70]. An amplification factor G=(integral)p [sub two-phase][sup 2]df/(integral)p[sub single-phase][sup 2]df is measured as a function of the gross void fraction (beta) of the air bubbles. Results showed that G~(beta)[sup 2] and G~20 at (beta)=0.0065. The range of void fraction was limited due to the use of the bubble maker (located at the jet nozzle entrance) which consisted of a fritted ceramic disk that was housed in a glass Buchner funnel and fed compressed nitrogen gas. It is possible to improve this apparatus by using carbonated water at high pressure in a nozzle that consists of an array of small holes in a thin circular plate. This arrangement can be controlled to yield small bubbles with an average diameter of about 100 (mu)m in water. Larger void fractions are possible and the necessary constraint of having the resonant bubble frequencies well above the region of the low-frequency flow noise spectrum (<500 Hz) is obtained. A brief videotape will be shown. [Work supported in part by ONR.]