Synchronization characteristics of vortex shedding from in-line tube banks on weak acoustic resonance

Abstract

The present paper focuses on the synchronization behavior of vortex shedding in in-line tube banks with and without acoustic resonance. We have studied the characteristics of acoustic resonance generated by in-line tube banks with a tube pitch ratio of 2.8 in the flow direction. The single high peak in the sound pressure level spectrum was formed at the gap velocity from 5.0 m/s to 48.0 m/s. As the gap velocity increased, the peak frequency increased. The Strouhal number became approximately 0.145. At the gap velocity of 23.0 m/s, the acoustic resonance of the first mode occurred in the transverse direction. The flow patterns and vortex shedding of in-line tube banks at acoustic resonance have been experimentally investigated. The vortex flow field in the tube banks was measured by PIV with and without the acoustic resonance phenomenon. The alternative vortices were shed from each tube in tube banks with and without the acoustic resonance. A pair of vortices has been created at the top and bottom of the jet stream flowing between the gaps of two tubes. On the other hand, the phase-aligned alternative vortices were occasionally shed from each tube in tube banks. No acoustic resonance occurred, the phase-aligned alternative vortices were shed for 11.7 % of the 0.4 s period. When acoustic resonance occurred, the proportion of phase-aligned alternate vortices increased from 11.7 % to 31.0 %. The rate of increase in wall sound pressure is approximately equal to the rate of increase in vortex synchronization. The increase in wall sound pressure due to acoustic resonance is primarily due to the synchronization of vortices in the tube banks during the occurrence of weak resonance phenomena.

Keywords

• vortex
• acoustic resonance
• in-line tube banks
• flow pattern
• synchronization
• boiler