Particle Image Velocimetry Measurements of Aeroacoustic Sources of a Shallow Cavity in a Pipeline

Abstract

The aeroacoustic sources generated by flow over a ducted shallow cavity in the presence of a longitudinal plane sound wave are examined at various Strouhal numbers and sound intensities. The cavity is exposed to high Reynolds number fully developed pipe flow. Extensive particle image velocimetry (PIV) flow measurements are performed to characterize the unsteady velocity field and finite element analysis is used to obtain the acoustic velocity field. Howe's aeroacoustic integrand is then used to compute the spatial and temporal distributions of the aeroacoustic sources resulting from the cavity shear layer interaction with the sound field. The results show two aeroacoustic sources separated by a sink along the cavity shear layer. This distribution is different from that reported for the closed side-branch resonance case, which shows a single source at the downstream corner and a sink at the upstream corner of the cavity. The effect of the upstream corner geometry in the present case is, therefore, expected to be different from the case of side-branch resonance. The time-averaged sound power distribution is computed and the total sound power per cycle is compared with the aeroacoustic source strength measured by means of the standing wave method (SWM) (Mohamed, S., Graf, H. R., and Ziada, S., 2011, “Aeroacoustic Source of a Shallow Cavity in a Pipeline,” ASME Paper No. PVP2011-57437). The merits of these two methods in determining the aeroacoustic sources are highlighted.