Abstract
Grid-to-rod fretting wear resulting from fluid-induced vibrations in nuclear reactors has attracted great attention for its economy and safety concerns. To mitigate potential losses due to such fretting wear, the structural dynamics in the fluid-structure interaction system is required to be well understood and accurately estimated. Conventional approaches to describing the structural dynamics in such a system include analytical models and empirical correlations which were derived from fitting with experimental data. Meanwhile, a novel approach through numerical simulations to addressing the problem has been progressively developed and optimized, which features no requirements for force coefficients obtained from experiments as an input to analytical models. In the present paper, the dynamics of a flexible clamped-clamped cylindrical shell subjected to a turbulent external axial flow was studied numerically. The cylindrical shell was made of aluminium, 1 m in length, 14.7 / 14.16 mm in O.D. / I.D., and confined by a rigid tube of 40 mm in I.D.. In the fluid-structure interaction system, fluid and structural domains were spatially discretized by finite volume method (FVM) and finite element method (FEM), respectively. The mesh scale in the fluid domain was comparable with that in the literature. For the discretized sub-domains of study, the fluid was described by the Navier-Stokes equations, and the structure was described by the Euler-Bernoulli beam equation, the fluid and structure systems were coupled on their interface by exchanging force information at each calculation time step. The solvers to the two systems herein were CFX Ansys and Mechanical Ansys, respectively. Thus no third party code such as a commercial package MpCCI, is required to couple the two calculation schemes. The simulation results show good agreement with experimental data in the magnitude of oscillating amplitude, and witness less difference with the experimental data than that by many empirical correlations. The time series oscillating displacement fluctuates around its original equilibrium state as periodically dissipating energy to and obtaining energy from the surrounded fluid. It is also found that the fundamental frequency obtained from the simulations is in quantitatively consistent with that by empirical correlations. The dimensionless displacement distribution along the cylinder span is in quantitatively consensus with the mode shape in the literature. The simulation approach also features its miscellaneous capabilities in predicting the fluid dynamics in fluid-structure interaction systems, such as fluid flow field, pressure distribution, turbulence intensity, etc. Experimental laboratories will also benefit from comparison opportunities.
