Predicting modal characteristics of a cluster of cylinders in axial flow: From potential flow solutions to coupled CFD–CSM calculations

Abstract

External fluid flow has a number of effects on the dynamics of a submersed structure: e.g., a solitary cylinder exposed to an external flow experiences added mass and damping due to the presence of the surrounding fluid. At high axial flow velocities relative to the stiffness of the cylinder, coupled instabilities such as flutter and divergence occur. Compared to a solitary cylinder, a cluster of cylinders also experiences inter-cylinder coupling: pressure perturbations in the fluid due to the movement or acceleration of one cylinder force another cylinder to move. Consequently, the different cylinders can move in organized patterns.In this contribution, modal characteristics of a 7-rod bundle will be predicted by linear theory as well as by coupled CFD-CSM (Computational Fluid Dynamics -Computational Structure Mechanics) calculations. In the first part, fluid forces which lead to coupling of motion are computed with classical potential flow theory and URANS (Unsteady Reynolds-Averaged Navier-Stokes). Those forces are divided in a contribution in phase with the acceleration and a contribution in phase with the velocity of a cylinder. In the second part, modal characteristics of a 7 cylinder bundle are computed with coupled CFD-CSM simulations. The initial perturbations, which are required for the time-domain simulations come from a simplified structural model, with potential flow coupling between cylinders. The results are compared to linear theory. In the final part, approximations are proposed to predict upper and lower bounds of eigenfrequencies and damping, using calculations with only one cylinder.

A multi-stage approach of simulating turbulence-induced vibrations in a wire-wrapped tube bundle for fretting wear prediction

“…The proposed procedure consists of four major parts, as summarized in Fig- in the work of De Ridder [36], but the relevant parts are briefly summarized in section 4.…”

“…The result is that each flexural mode corresponds to a range of natural frequencies and damping ratios rather than a single value. Using a similar approach as in [31], the modal characteristics of a cluster of cylinders were determined using two-way coupled CFD-CSM simulations by De Ridder et al [36], the results of which are built upon in this research.…”

A study of the vibration of a horizontal U-bend subjected to an internal upwards flowing air–water mixture

“…This method is implemented in the in-house coupling code Tango, which handles the communication between the flow solver and the structural solver. The code Tango has been programmed in C++ and has been validated for a number of different applications (Annerel et al (2014); De Ridder et al (2015Ridder et al ( , 2017), including the simulation of sloshing in a tank where the fluid subproblem was modelled with the VOF technique (Degroote et al (2010)) similar to the method applied in the flow problem presented in this paper. As both solvers are commercial codes and therefore are black-box solvers, the Jacobian of the FSI-system is unknown.…”

Experimental study of fluid structure interaction on fuel assemblies on the ICARE experimental facility

“…From the literature it is known that when a network of structures subject to an excitation is immersed in a liquid, the interaction between the fluid and the structure creates a coupling between the di↵erent structures which would otherwise behave independently (Païdoussis, 1998(Païdoussis, , 2008De Ridder et al, 2013, 2017.…”