Effects of branch length and chamfer on flow-induced acoustic resonance in closed side branches

The flow-induced acoustic resonance phenomenon may produce excessive vibrations of components in pipe systems. In this study, the effects of branch length and edge geometry on the acoustic resonance characteristics of closed side branches are investigated experimentally. Three different aspect ratios of L/d = 8, 10 and 12, where L is the branch length and d is the branch diameter, are investigated with Mach number up to 0.28. The results show that, for all the tested configurations, the second hydrodynamic mode only excites the first acoustic mode due to the small diameter of the side branches. The maximum normalized pulsation amplitude at the first acoustic mode decreases in branch length. The influence of branch length on the Strouhal numbers at onset of resonance is weak. It is about 0.55 for the first hydrodynamic mode in the case of sharp edge. The maximum normalized pulsation amplitudes are excited at a Strouhal number close to 0.4. Two different chamfers of angle 45° and C = 2.5 and 5 mm, where C is the width of the chamfered edge, are investigated. The results illustrate that the maximum normalized pulsation amplitude and the Strouhal number at onset of resonance both decrease significantly in chamfer width, which indicates chamfering is an effective method to attenuate undesirable acoustic resonance induced by closed side branches in pipe system.