Fluid-Structure Interaction Simulations in Applications for Nuclear Engineering
Abstract
Nuclear reactors pump coolant through their core and heat exchangers at massive
mass flow rates to sustain energy production. These demanding requirements push
engineers to extreme levels of optimization to safely sustain the transfer of energy. High
flow rates introduce the possibility of flow-induced vibrations. Reactor core and heat-exchanger/
steam generator designs go through many stages of experimentation to ensure
that problematic flow-induced vibrations do not arise. Advances in computational
capabilities introduce the possibility of creating predictive simulations that accelerate the
iterative design process and replace expensive physical experiments. Simulation
methods for fluid-structure interactions are rapidly developing and undergoing extensive
verification and validation. Computational fluid dynamics code Nek5000 and
computational structural mechanics code Diablo have been coupled to create a highly
scalable, high-fidelity fluid-structure interaction code. A fully coupled model of
crossflow through a tube bundle has been simulated using the Nek5000-Diablo code for
validation purposes. Simulations at three velocities were performed to test the method’s
capabilities of capturing the onset of large amplitude vibrations that occur at a critical
velocity for the tube bundle. The simulation results compared favorably to the
experiment on which it was based and gave further insight into the mechanisms behind
the vibrations. A 7-pin bundle of wire-wrapped fuel pins was simulated using Nek5000
and the forces exerted on the pins captured. A scheme was developed to synthesize force
histories of indefinite length replicating the Nek5000 force signals, forming a modified
one-directional coupling procedure. Multiple structure simulations were performed,
observing the effects of pin-to-pin, and pin-to shroud contact scenarios on the resulting
vibrations. The shroud was found to effectively limit vibrations to short wave-lengths on
the order of 1/6^th helical pitch even when extensive gaps between pins formed in the
reactor. Both the one-way and two-way coupling methods are successful in capturing the
fluid and structure behaviors and provide a convenient method of analysis for these
geometries.
Citation
Brockmeyer, Landon Mitchell (2018). Fluid-Structure Interaction Simulations in Applications for Nuclear Engineering. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /174591.