Bi-stable flow in tube arrays

Abstract

An experimental study of bi-stable flow has been performed. Three tube array geometries were used; two normal triangular tube arrays with pitch-to-diameter ratios (P/d) of 1.32 and 1.58 and a parallel triangular tube array with Pjd = 1.375. Firstly, the surface pressure acting on an instrumented cylinder (featuring 36 circumferential pressure taps at midplane) due to the motion of a neighbouring cylinder was examined. The tubes were arranged in a normal triangular tube array (Pjd = 1.32 and 1.58) and were mounted in a draw-down wind tunnel. The fluid forces acting on the instrumented cylinder were calculated by integrating the surface pressure distributions with respect to angular position. The gradients of these forces with respect to the displacement of the neighbouring tube have been estimated, as these determine the onset of stiffness-controlled fluidelastic instability in a flexible tube array. It has been found that these parameters are largely independent of Reynolds number. Also, as in previous studies, bi-stable flow has been observed in the tube array with P/d = 1.58 for all displacements and at intermediate Reynolds numbers.