Flow-induced acoustic resonances in closed tandem side branches with large diameter

Abstract

Flow-induced acoustic resonances in closed tandem side branches with large branch diameter are investigated experimentally. The diameters of the main pipe and branches are 305 mm and 64 mm, respectively. Three single branches with different lengths, L/d = 5.86–8.52, are investigated. The first and second hydrodynamic modes are excited at Strouhal numbers close to 0.4 and 0.8, respectively. The normalized pulsation amplitude of a certain mode decreases in branch length. For tandem branches, the resonances are rarely affected by the distance in the investigated range of Lt/D = 3.28–9.84. The branch number has no effects on dominant frequencies, but the critical velocity increases in branch number. In the delayed regions, the amplitudes in tandem branches are enhanced remarkably due to change in resonance mode. The maximum amplitudes excited by the first acoustic mode in the tandem branches, which are much higher than that in the single branch, are all in delay regions and close.