Author(s)

P. McKinnis, B. Miller & A. Ruggles

Abstract

Acoustic standing waves may be established in main gas delivery lines and are caused by resonance in branch lines. The branch line resonance frequency is normally determined from the geometry of the branch. Data are presented that show the branch line standing wave couples with the main line standing wave, and a range of side branch resonance frequencies are possible, with multiple frequencies existing in the side branch at the same time in some cases. This phenomenon is important to gas delivery systems where acoustic frequencies and loads must be predicted to facilitate design of the system components. 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, L nc fnatural 4 = ..... 7 , 5 , 3 , 1 = n (1) where c is the sound speed and the characteristic length, L, is the branch length. The branch length is sometimes extended by some fraction of the diameter.

Keywords

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