Vibration Excitation Forces in a Normal Triangular Tube Bundle Subjected to Two-Phase Cross Flow

Abstract

This paper presents test results of vibration forces in a normal triangular tube bundle subjected to air-water cross-flow. The dynamic lift and drag forces were measured with strain gage instrumented cylinders. The array has a pitch-to-diameter ratio of 1.5, and the tube diameter is 38 mm. A wide range of void fraction and fluid velocities were tested. The experiments revealed significant forces in both the drag and lift directions. Constant frequency and quasi-periodic fluid forces were found in addition to random excitation. These forces were analyzed and characterized to understand their origins. The forces were found to be dependent on the position of the cylinder within the bundle. The results are compared with those obtained with flexible cylinders in the same tube bundle and to those for a rotated triangular tube bundle. These comparisons reveal the influence of quasi-periodic forces on tube motions.

Experimental assessment of equivalent loads and dynamic parameters on vibration induced by two-phase crossflow in tube bundles

“…Conversely, only few experimental data for turbulence-induced vibration mechanism under conditions twophase flow are available, which is somehow surprising since this vibration mechanism is unavoidable, and is always present in heat exchanger tube bundles. Actually, more recent experimental studies (ZHANG et al, 2007;PERROT et al, 2011) have shown that there is a lack of knowledge in this mechanism since they found out that it consists of turbulence and periodic components, which have not been reported in literature before.…”

“…Furthermore, these mechanisms related to quasi-periodic forces are currently been studied and information about its causes is scarce. Anyway, it is worth pointing out that Zhang et al (2007) and Perrot et al (2011) found these mechanisms with quasi-periodic forces by analyzing the buffeting vibration induced by two-phase flow.…”

“…Several other studies report the use of strain gauges to assess force in FIV (TAYLOR et al, 1988;TAYLOR et al, 1989;AXISA et al, 1990;PETTIGREW et al, 1995;PETTIGREW et al, 2002;PETTIGREW et al, 2005;PERROT et al, 2011). In strain gauge applications, in which a secondary quantity (other than strain) is needed, a preliminary calibration step is required, in which a known loading condition is used to relate the measurement output to that desired quantity.…”

“…Despite this, in most cases flow-induced forces imply distributed forces and the instrumentation up-to-date can hardly estimate its characteristics directly (say frequency components and amplitude), unless a set of hypotheses is adopted. For this reason, and for the sake of easiness, some authors (ZHANG et al, 2007;PERROT et al, 2011) prefer the estimation of an equivalent force that is capable of representing a set of forces under some hypotheses.…”

“…Recently, another type of quasi-periodic forces have been reported in literature (ZHANG et al, 2007;PERROT et al, 2011), however only Zhang et al (2007) make more precise observations about the results. Zhang et al (2007) found quasi-periodic forces in both the parallel and transverse directions.…”