Cross-Flow-Induced Vibrations Deep Inside a Closely-Packed Tube Bank

Abstract

<p> Heat-exchangers designed and fabricated in accordance with the existing design standards may be susceptible to damage as a result of excessive tube vibrations caused by the shell-side fluid flow. The present investigat ion was undertaken to further our understanding of the vibration behaviour of tube arrays. </p> <p> An experimental facility and techniques have been developed by means of which the major mechanisms that cause flow-induced vibrations in tube arrays due to cross-flow can be produced and properly identified. </p> <p> The experiments were conducted in a low-speed windtunnel having 305 x 305 mm.working section. The tube-bundle was a parallel-triangular tube-array with pitch/diameter = 1.375 . The array was 27 rows deep with 5 tubes in each row . The tubes were designed such that they could be conveniently removed from outside the wind-tunnel, in order to facilitate studying the effect of tube-bundle size on vibration and flow characteristics . Nineteen identical tubes in the middle of the tube-array were movable and specially designed so that natural frequency and damping could be controlled precisely over a range of values. </p> <p> The experiments have verified that deep inside a closely-packed tube-bank the existence of discrete vortex shedding is not a working hypothesis and the response of a tube in a tube-bundle is expected to be a function of Reynolds number and the number of upstream rows of tubes. From the flow-field velocity power-spectra obtained for the array tested and from the available data existing in the literature, it is seen that there is a strong possibility of predicting the dominating frequency in the flow from a universal Strauhal number. For the first time a fluidelastic stability boundary for the array has been derived and it is noticed that the slope of this boundary is significantly different from that derived by other authors from theoretical considerations. </p>