Flow Induced Acoustic Resonance and Vortex Shedding From Staggered Tube Banks

In the present paper our attention is focused on the relation between the vortex shedding phenomena and acoustic resonance in tube banks. We measured a spectrum, coherence function, phase delay of velocity fluctuations in the tube banks and sound pressure level at the duct exit. A model of tube banks had used the same pitch ratio as that of a boiler heat exchanger of a commercial use. As a result, we found three types of vortex shedding with different Strouhal number, 0.29, 0.22 and 0.19. The vortex shedding of S_t = 0.29 and 0.22 were generated inside of the tube banks. On the other hand S_t = 0.22 and 0.19 were in the wake of the last row of the tube banks. The velocity fluctuation and the periodicity of the vortex shedding were the most intense in the wake of the second row of the tube banks in whole area of the tube banks. When acoustic resonance generated at the natural frequency of the duct, 342.5Hz, at a gap velocity of 39.2m/s, we found two types of vortex shedding with different frequencies, mainly about 342.5Hz (S_t = 0.29) and 262.5Hz (S_t = 0.22), inside of the tube banks. The amplitude of velocity fluctuation due to the vortex shedding became large in accordance with the generation of the acoustic resonance which has the fundamental natural frequency of the acoustic resonance in the transverse direction of the duct.