This paper is the second part of the two-part review article presenting an overview of mechanics of pipes conveying fluid and related problems such as the fluid-elastic instability under conditions of turbulence in nuclear power plants. In the first part, different types of modeling, dynamic analysis and stability regimes of pipes conveying fluid restrained by elastic or inelastic barriers were described. The dynamic and stability behaviors of pinnedpinned, clamped-clamped, and cantilevered pipes conveying fluid together with curved and articulated pipes were discussed. Other problems such as pipes made of viscoelastic materials and active control of severe pipe vibrations were considered. The first part was closed by conclusions highlighting resolved and nonresolved controversies reported in the literature. The second part will address the problem of fluidelastic instability in single- and twophase flows and fretting wear in process equipment, such as heat exchangers and steam generators. Connors critical velocity will be discussed as a measure of initiating fluidelastic instability. Vibro-impact of heat exchanger tubes and the random excitation by the cross-flow can produce a progressive damage at the supports through fretting wear or fatigue. Antivibration bar supports used to limit pipe vibrations are described. An assessment of analytical, numerical, and experimental techniques of fretting-wear problem of pipes in heat exchangers will be given. Other topics related to this part include remote impact analysis and parameter identification, pipe damage-induced by pressure elastic waves, the dynamic response and stability of long pipes, marine risers together with pipes aspirating fluid, and carbon nanotubes conveying fluid. DOI: 10.1115/1.4001270

Mechanics of Pipes Conveying Fluids—Part II: Applications and Fluidelastic Problems

Fluidelastic instability study in a rotated triangular tube array subject to two-phase cross-flow. Part I: Fluid force measurements and time delay extraction

Almost all the available data about fluidelastic instability of heat exchanger tube bundles concerns tubes that are axisymmetrically flexible. In those cases, the instability is found to be mostly in the direction transverse to the flow. Thus, the direction parallel to the flow has raised less concern in terms of bundle stability. However, the flat bar supports used in steam generator for preventing U-tube vibration may not be as effective in the in-plane direction than in the out-of-plane direction. The possibility that fluidelastic instability can develop in the flow direction must then be assessed. In the present work, tests were done to study the fluidelastic instability of a cluster of seven tubes much more flexible in the flow direction than in the lift direction. The array configuration is rotated triangular with a pitch to diameter ratio of 1.5. The array was subjected to two-phase (air-water) cross flow. Fluidelastic instability was observed when the flexible tubes were located at the center of the test section and also when the seven flexible tubes were placed over two adjacent columns. No instability was found for a single flexible tube in a rigid array nor for the case where the seven flexible tubes were placed in a single column. Tests were also done with tubes that are axisymmetrically flexible for comparison purposes. It was found that fluidelastic instability occurs at higher velocities when the tubes are flexible only in the flow direction. These results and additional wind tunnel results are compared to existing data on fluidelastic instability. Two-phase flow damping results are also presented in this paper.

Fluidelastic Instability of an Array of Tubes Preferentially Flexible in the Flow Direction Subjected to Two-Phase Cross Flow

Experimental and Numerical Characterization of Flow-Induced Vibration of Multispan U-tubes

The development of a theoretical model for fluidelastic instability in tubes arrays is presented. Based on the simple model of Lever and Weaver, it considers a group of 7 tubes which move in both the streamwise and transverse directions. The analysis does not constrain either tube frequency or relative mode shape so that the tubes’ behaviour evolves from a perturbation naturally. No additional empirical input is required. A particular case is used to evaluate the model’s performance and the ratio of streamwise to transverse natural frequency is varied. Both streamwise and transverse fluidelastic instability are predicted and the results agree well with experimental observations.Copyright © 2015 by ASME

M. Ruël

Papers

Fluidelastic instability tests on an array of tubes preferentially flexible in the flow direction