Author(s)

M. Shehane, E. Moore & A. Ruggles

Abstract

Acoustic standing waves may be established in main gas delivery lines that are caused by resonance in branch lines. Conventional theory predicts branch line resonance frequency from the geometry of the branch and main line diameter. Data are presented that show the branch line standing wave couples with the main line standing wave, and a range of side branch resonance amplitude and frequency values are possible. Further, the resonance amplitude varies over long periods, and data acquisition using a short moving time window is employed to examine the Power Spectral Density (PSD) as a function of time. Peak amplitude values from the moving time window PSDs are identified and displayed in a Probability Density Function (PDF). The combined PSD and PDF information allows repeatable system characterization as a function of operating parameters and geometry, and data of this type are presented from a low-pressure air test facility. Keywords: branch line resonance, acoustics, standing waves, fluid-structure interaction. 1 Introduction Small branch lines off larger main delivery lines can exhibit acoustic resonance. Branch lines with a reflective obstruction, such as a valve or instrument, are susceptible to a ¼ wavelength standing wave, with a pressure node positioned near where the branch meets the main line, and a pressure anti-node positioned at the obstruction. Of course, higher modes are possible with an odd number of quarter wavelengths existing in the branch such that,

Keywords

branch line resonance, acoustics, standing waves, fluid-structure interaction.