VORTEX SHEDDING IN AN IN-LINE TUBE BUNDLE WITH LARGE TUBE SPACINGS

An in-line tube bundle with large spacing ratios is tested in air and water flows to examine the mechanisms of vorticity shedding and acoustic resonance. The tests include correlation measurements of the velocity fluctuations, and visualization of the flow structure at resonant and non-resonant conditions. Vorticity shedding is found to occur at two distinct modes. The first mode, which occurs at low upstream turbulence level, is generated by a “global” jet instability, resulting in a well defined phase relation between the flow activities in adjacent wakes. The second mode occurs when the upstream turbulence level is increased. It results from “local” wake instabilities, and therefore, the flow activities in adjacent wakes are not correlated. The nature of both modes and their relationship to the excitation mechanism of acoustic (or fluid) resonances are detailed. The paper also includes a classification of in-line tube bundles according to the flow instability which dominates in each class. © 1993 by Academic Press, Inc.