Effect of Preferential Flexibility Angle on Fluidelastic Instability of a Rotated Triangular Tube Bundle

摘要

In the operation of shell-and-tube heat exchangers, tube vibration can be induced by fluid flowing over the tube array. The region of concern in Steam Generators (SG) is the upper most U-bend region, where the flow crosses a large number of tubes which can cause significant hydraulic resistance. This hydraulic resistance forces the flow to change direction. As a result the flow leaves the tube bundle at different angles of attack from ranging 0° to 90°. From a fluidelastic instability point of view, the tube bundle is excited by oblique cross flow. The purpose of this paper is to examine the instability phenomena in a rotated triangle tube bundle subjected to oblique single phase cross flow. Based on experimental mode shapes and measured fluidelastic forces, Connors [1] developed a simple stability criterion for a tube bundle subjected to cross flow: U{sub}c/fD = K(2πζm/ρD{sup}2){sup}b (1) where, fluidelastic instability is expressed in terms of a dimensionless velocity, U{sub}c/fD, and a dimensionless mass-damping term, 2πζm/ρD{sup}2, U{sub}c is the critical pitch velocity for fluidelastic instability, f the tube natural frequency, D the tube diameter, ζ the damping ratio, ρ the density of the fluid, and m the tube mass per unit length, which includes the hydrodynamic mass and the mass of the fluid inside the tube. In the simplest model, the exponent b is 0.5. Generally the exponent depends on tube bundle configuration and dimensionless mass damping term [2]. The fluidelastic instability constant K is usually determined experimentally.