ASA 125th Meeting Ottawa 1993 May

4pAO9. Enhancement of hydrodynamic flow noise by the regulation of air bubbles in a turbulent water jet.

Murray S. Korman

Dept. of Phys., U.S. Naval Academy, Annapolis, MD 21402

Lawrence A. Crum

Univ. of Washington, Seattle, WA 98105

An experiment is performed to show that the near-field hydrodynamic flow noise (generated by a submerged water jet) is enhanced when the turbulent flow is modified to become a two-phase flow containing air bubbles. Pressure spectra, in the band 5--5000 Hz, are measured using a digital spectral analyzer from signals generated by a hydrophone placed at the axial and radial position (Z=4D and R=4D) from the nozzle exit diameter, D=0.635 cm. 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. Here, we measure (beta) to be the ratio of gas volume flow rate (through the bubblemaker located at the nozzle entrance) to the water volume flow rate, Q[sub g]/Q[sub w]. The amplification G is measured as a function of (beta) by keeping Q[sub w] constant (the nozzle velocity U=13.8 m/s) and varying Q[sub g]. Results show that G~(beta)[sup 2] and G~20 at (beta)=0.0065. The mean-squared pressure fluctuation p[sup 2](identically equal to)(integral)p[sub two-phase][sup 2] df is measured as a function of U by keeping Q[sub g] fixed and varying Q[sub w]. Results show that p[sup 2]~U[sup m], where m=3.6, 4.3, and 4.7 for Q[sub g]=50, 86, and 136 sccm, respectively. [Work supported by NCPA.]