Measurement of Critical Velocities for Fluidelastic Instability Using Vibration Control

Abstract

Fluidelastic effects may be responsible for instabilities of heat exchanger tubes when the fluid flow reaches the critical velocity. The fluidelastic phenomenon is usually studied on experimental mock-ups, which may display only one critical velocity. In this paper, a method based on active vibration control is proposed in order to derive several critical velocities for fluidelastic instability corresponding to several different values of damping, which is artificially varied on the same mock-up. Experimental tests are performed on a flexible tube equipped with piezoelectric actuators in a rigid array under air-water cross-flow. It is shown that the reduced critical velocities thus obtained fit well in a classical stability map. [S0739-3717(00)01603-2]

Vibro-Impact Experiments and Computations of a Gap-Supported Tube Subjected to Single-Phase Fluid-Elastic Coupling Forces

“…One may notice, from equations (5) and (13), that the tube/support interaction couples the system unconstrained modes. Indeed, during contact, one obtains:…”

“…2 and 3. It is, essentially, the one used in [12][13][14] in their tests, however a new instrumented tube with quite different modal frequency was used in the present experiments. Furthermore, the present experiments were designed for flow-excited vibro-impacting on an instrumented loose support.…”

“…, the added mass m C being assumed independent of the flow velocity. In order to explore the full range of experimental reduced velocity -well beyond the fluid-elastic stability boundary of the "normal" system -the analog feedback stabilization technique [12][13][14] has been adopted. It is, essentially, the one used earlier by Antunes et al [9] in their feedback controlled instability tests, but with reversed polarity.…”

“…Therefore, based on the active vibration control method proposed by Caillaud et al [12][13][14], new experiments have recently been performed at CEA-Saclay on the same experimental rig, consisting on a flexible tube (vibrating along the lift direction) inserted in a rigid square bundle. First, the linearized fluid-elastic coupling coefficients, as well as the turbulence excitation, were identified for a significant range of reduced velocity, in water cross-flow.…”

Fluid-Elastic Coefficients in Single Phase Cross Flow: Dimensional Analysis, Direct and Indirect Experimental Methods

“…This instability can be described as a self-excited feedback mechanism between the motion of the structure and the fluid forces. Since the pioneering work of Tanaka and Takahara [1], several authors [2][3][4][5][6][7][8][9][10] measured the fluid-elastic force to feed the stability criterion models developed by Connors [11], Blevins [12], Chen [2,3], Lever and Weaver [13][14][15], Price and Païdoussis [16][17][18], Granger et al [19,20] and Tanaka et al [21].…”