Page 323 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Simulation of flow-induced 6.2.2

vibrations in tube bundles
using URANS

†
J. De Ridder*, L. De Moerloose*, K. Van Tichelen , J. Vierendeels*,
J. Degroote*
*Department of Flow, Heat and Combustion Mechanics, Ghent University, Ghent, Belgium,
†
Belgian Nuclear Research Centre, Mol, Belgium

6.2.2.1 Introduction

Flow-induced vibration (FIV) is a global term to indicate that the vibrations are caused
by the interaction of a structural component with a fluid flow surrounding it (De Ridder,
2015). A common classification is based on the excitation mechanism: extraneously,
instability-, and movement-induced vibrations (Naudascher and Rockwell, 2012).
The extraneously induced vibrations consist of all flow-induced vibrations in
which the fluid flow carries an external pressure excitation. An example of this type
of instability is vibration caused by turbulence in the flow. As small-scale vortices are
modeled instead of resolved in unsteady Reynolds-averaged Navier-Stokes (URANS)
simulations, the excitation due to small-scale pressure fluctuations cannot be resolved
with this type of turbulence modeling. By contrast, large-eddy simulations (LES) or
direct numerical simulation (DNS) can be used to quantify the spectrum of the pres-
sure fluctuations (De Ridder et al., 2016a).
In the instability-induced vibrations, the fluid flow becomes unstable due to the
geometry of the structure involved. This happens, for example, in vortex-induced
vibrations. As a fluid flow crosses a bluff body, the wake behind it can, under the right
conditions, become unstable, with vortices being shed. The resulting time-varying
asymmetrical forces can cause vibrations. It is important to note that the instability
in the flow should be present even if the structure is standing still but that the insta-
bility in the flow can also be modified by the vibration. This kind of instabilities can be
calculated using fluid-structure interaction (FSI) simulations based on URANS for the
flow, as long as URANS can resolve the large-scale fluctuation in the flow (De Ridder
et al., 2016b; De Moerloose, 2016).
A third flow-induced vibration mechanism consists of a reinforcing feedback
between structural motion and incident forces. This type of vibrations is known as
movement-induced vibrations. Some examples of movement-induced vibrations are
the collapse of the Tacoma Narrows Bridge, the fluttering of tents and flags, and the
galloping of electricity lines and fluid-elastic instabilities in steam generators. Also
tubes in bundles with axial flow can undergo this type of vibration, which can be cal-
culated using FSI simulations based on URANS for the flow (De Ridder et al., 2015).

Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors. https://doi.org/10.1016/B978-0-08-101980-1.00019-3
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