Aeroacoustic Source of a Shallow Cavity in a Pipeline

Abstract

The flow-induced acoustic source of an axisymetric shallow cavity, coupled to longitudinal acoustic modes in a pipeline is characterized experimentally for circular pipes conveying fully developed turbulent flow. This aeroacoustic source is generated due to the interaction of the cavity shear layer oscillation with the resonant acoustic field in the pipe. The distributed aeroacoustic source is modeled by a lumped acoustic dipole source which is dependent on the Strouhal number and the acoustic particle velocity at the cavity. The amplitude and phase of this source are determined experimentally and presented in the form of a dimensionless complex source term.

Aeroacoustic sources generated by flow–sound interaction in a T-junction

“…4. This difference also agrees well with the measurements of shear layer excitation sources for deep and shallow cavities which showed that higher order shear layer modes have much weaker excitation sources than those generated by the lower shear layer modes (Graf and Ziada, 2010;Mohamed et al, 2011;Nakiboglu et al, 2011). The second difference is that the accumulated sound power for Mode B oscillation is a small negative value, whereas the power computed for Mode A was positive.…”

“…It is well established that the excitation sources of shear layers become weaker at large amplitude acoustic pulsation, and especially for sources associated with higher shear layer modes. For example, Mohamed et al (2011) demonstrated that the second shear layer mode of a shallow cavity becomes negative at an excitation level of ðU ac =V m Þ E4%. In the present case, the excitation level was even higher due to external excitation ðU ac =V m Þ¼6.2%, and therefore the total accumulated power is negative, indicating that some of power provided by the loudspeakers is absorbed by the flow oscillations in the T-junction.…”