Coupling of vortex shedding with the fundamental resonant mode of a resonator tube

An investigation of the coupling between the vortex shedding from a trip rod with triangular cross-section and a resonant mode of a tube is presented. The physical experiments were conducted using a shallow water channel; this system represents an hydraulic analogy of the acoustic resonator tube in airflow. The resonator tube differs from that used in previous physical experiments as a result of rounding the tips and increasing the size of the trip rod. Rounding the tips is found to reduce the level of vortex shedding from the tips. This increases the amplitude of the tube resonance as a result of lower damping of the oscillations. The spacing between the trip rod and the resonator tube leading to maximum resonance amplitude increases with increasing flow velocity. Numerical experiments using aeroacoustic theory to explain the transfer of energy between the resonance field and the mean flow field predict well this observed trend, as well as the source of wave energy.