An Investigation of Resonance Conditions for Pulsating Flow of Air through an Orifice in a Pipe

A review of some previous studies of pulsating air flow through orifices in pipes is presented. In particular, the authors comment on the significance of inertia effects, the use of Strouhal number as a non-dimensional parameter, and the effect of phase change on time-dependent variables. Attention is drawn to the possible importance of the previously neglected interaction between the effects of orifices as acoustical filters and as meters of pulsating flow.

Using complex variable analysis, a theoretical model based on plane acoustic waves yields, for resonance conditions, relationships between frequency, pressure and geometry variables. These were investigated experimentally for a 1-in diameter pipe with different orifice diameters for a range of frequencies up to 180 Hz.

The results indicate that accurate derivation of mass flow rates from pressure measurements across an orifice in a pipe depends on taking into account the effects of wave action at all frequencies. This would avoid the rig-dependent limitations to which experimental work on pulsating gas flow through an orifice in a pipe is subject.